The Relative Importance of Body Size and Paleoclimatic Change as Explanatory Variables Influencing Lineage Diversification Rate: An Evolutionary Analysis of Bullhead Catfishes (Siluriformes: Ictaluridae)
Identifieur interne : 003D17 ( Istex/Corpus ); précédent : 003D16; suivant : 003D18The Relative Importance of Body Size and Paleoclimatic Change as Explanatory Variables Influencing Lineage Diversification Rate: An Evolutionary Analysis of Bullhead Catfishes (Siluriformes: Ictaluridae)
Auteurs : Michael Hardman ; Lotta M. HardmanSource :
- Systematic Biology [ 1063-5157 ] ; 2008-02.
Abstract
We applied Bayesian phylogenetics, divergence time estimation, diversification pattern analysis, and parsimony-based methods of ancestral state reconstruction to a combination of nucleotide sequences, maximum body sizes, fossils, and paleoclimate data to explore the influence of an extrinsic (climate change) and an intrinsic (maximum body size) factor on diversification rates in a North American clade of catfishes (Ictaluridae). We found diversification rate to have been significantly variable over time, with significant (or nearly significant) rate increases in the early history of Noturus. Though the latter coincided closely with a period of dramatic climate change at the Eocene-Oligocene boundary, we did not detect evidence for a general association between climate change and diversification rate during the entire history of Ictaluridae. Within Ictaluridae, small body size was found to be a near significant predictor of species richness. Morphological stasis of several species appears to be a consequence of a homoplastic increase in body size. We estimated the maximum standard length of the ictalurid ancestor to be approximately 50 cm, comparable to Eocene ictalurids (Astephus) and similar to modern sizes of Ameiurus and their Asian sister-taxon Cranoglanis. During the late Paleocene and early Eocene, the ictalurid ancestor diversified into the lineages represented by the modern epigean genera. The majority of modern species originated in the Oligocene and Miocene, most likely according to a peripheral isolates model of speciation. We discuss the difficulties of detecting macroevolutionary patterns within a lineage history and encourage the scrutiny of the terminal Eocene climatic event as a direct promoter of diversification.
Url:
DOI: 10.1080/10635150801902193
Links to Exploration step
ISTEX:7BB9A3067B7287CA2E8CEB47C586DFE0C34B3A42Le document en format XML
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Hardman</name><affiliation><mods:affiliation>Laboratory of Molecular Systematics, Finnish Forest Research Institute, Jokiniemenkuja 1, 01301, Vantaa, Finland</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: m.hardman@mac.com</mods:affiliation></affiliation></author></analytic><monogr></monogr><series><title level="j">Systematic Biology</title><idno type="ISSN">1063-5157</idno><idno type="eISSN">1076-836X</idno><imprint><publisher>Taylor & Francis</publisher><date type="published" when="2008-02">2008-02</date><biblScope unit="volume">57</biblScope><biblScope unit="issue">1</biblScope><biblScope unit="page" from="116">116</biblScope><biblScope unit="page" to="130">130</biblScope></imprint><idno type="ISSN">1063-5157</idno></series></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">1063-5157</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract">We applied Bayesian phylogenetics, divergence time estimation, diversification pattern analysis, and parsimony-based methods of ancestral state reconstruction to a combination of nucleotide sequences, maximum body sizes, fossils, and paleoclimate data to explore the influence of an extrinsic (climate change) and an intrinsic (maximum body size) factor on diversification rates in a North American clade of catfishes (Ictaluridae). We found diversification rate to have been significantly variable over time, with significant (or nearly significant) rate increases in the early history of Noturus. Though the latter coincided closely with a period of dramatic climate change at the Eocene-Oligocene boundary, we did not detect evidence for a general association between climate change and diversification rate during the entire history of Ictaluridae. Within Ictaluridae, small body size was found to be a near significant predictor of species richness. Morphological stasis of several species appears to be a consequence of a homoplastic increase in body size. We estimated the maximum standard length of the ictalurid ancestor to be approximately 50 cm, comparable to Eocene ictalurids (Astephus) and similar to modern sizes of Ameiurus and their Asian sister-taxon Cranoglanis. During the late Paleocene and early Eocene, the ictalurid ancestor diversified into the lineages represented by the modern epigean genera. The majority of modern species originated in the Oligocene and Miocene, most likely according to a peripheral isolates model of speciation. We discuss the difficulties of detecting macroevolutionary patterns within a lineage history and encourage the scrutiny of the terminal Eocene climatic event as a direct promoter of diversification.</div></front></TEI><istex><corpusName>oup</corpusName><editor><json:item><name>Allan Baker</name><affiliations><json:string>Laboratory of Molecular Systematics, Finnish Forest Research Institute, Jokiniemenkuja 1, 01301, Vantaa, Finland</json:string><json:string>E-mail: m.hardman@mac.com</json:string></affiliations></json:item></editor><author><json:item><name>Michael Hardman</name><affiliations><json:string>Laboratory of Molecular Systematics, Finnish Forest Research Institute, Jokiniemenkuja 1, 01301, Vantaa, Finland</json:string><json:string>E-mail: m.hardman@mac.com</json:string></affiliations></json:item><json:item><name>Lotta M. Hardman</name><affiliations><json:string>Laboratory of Molecular Systematics, Finnish Forest Research Institute, Jokiniemenkuja 1, 01301, Vantaa, Finland</json:string><json:string>E-mail: m.hardman@mac.com</json:string></affiliations></json:item></author><subject><json:item><value>Clade assymmetry</value></json:item><json:item><value>Eocene extinction</value></json:item><json:item><value>historical biogeography</value></json:item><json:item><value>North American ichthyofauna</value></json:item><json:item><value>relaxed clock</value></json:item><json:item><value>speciation</value></json:item><json:item><value>Cenozoic freshwater fishes</value></json:item></subject><arkIstex>ark:/67375/HXZ-F7LCQR6L-3</arkIstex><language><json:string>unknown</json:string></language><originalGenre><json:string>research-article</json:string></originalGenre><abstract>We applied Bayesian phylogenetics, divergence time estimation, diversification pattern analysis, and parsimony-based methods of ancestral state reconstruction to a combination of nucleotide sequences, maximum body sizes, fossils, and paleoclimate data to explore the influence of an extrinsic (climate change) and an intrinsic (maximum body size) factor on diversification rates in a North American clade of catfishes (Ictaluridae). We found diversification rate to have been significantly variable over time, with significant (or nearly significant) rate increases in the early history of Noturus. Though the latter coincided closely with a period of dramatic climate change at the Eocene-Oligocene boundary, we did not detect evidence for a general association between climate change and diversification rate during the entire history of Ictaluridae. Within Ictaluridae, small body size was found to be a near significant predictor of species richness. Morphological stasis of several species appears to be a consequence of a homoplastic increase in body size. We estimated the maximum standard length of the ictalurid ancestor to be approximately 50 cm, comparable to Eocene ictalurids (Astephus) and similar to modern sizes of Ameiurus and their Asian sister-taxon Cranoglanis. During the late Paleocene and early Eocene, the ictalurid ancestor diversified into the lineages represented by the modern epigean genera. The majority of modern species originated in the Oligocene and Miocene, most likely according to a peripheral isolates model of speciation. We discuss the difficulties of detecting macroevolutionary patterns within a lineage history and encourage the scrutiny of the terminal Eocene climatic event as a direct promoter of diversification.</abstract><qualityIndicators><score>10</score><pdfWordCount>9985</pdfWordCount><pdfCharCount>64492</pdfCharCount><pdfVersion>1.3</pdfVersion><pdfPageCount>15</pdfPageCount><pdfPageSize>612 x 792 pts (letter)</pdfPageSize><refBibsNative>true</refBibsNative><abstractWordCount>252</abstractWordCount><abstractCharCount>1759</abstractCharCount><keywordCount>7</keywordCount></qualityIndicators><title>The Relative Importance of Body Size and Paleoclimatic Change as Explanatory Variables Influencing Lineage Diversification Rate: An Evolutionary Analysis of Bullhead Catfishes (Siluriformes: Ictaluridae)</title><pmid><json:string>18288621</json:string></pmid><genre><json:string>research-article</json:string></genre><host><title>Systematic Biology</title><language><json:string>unknown</json:string></language><issn><json:string>1063-5157</json:string></issn><eissn><json:string>1076-836X</json:string></eissn><publisherId><json:string>sysbio</json:string></publisherId><volume>57</volume><issue>1</issue><pages><first>116</first><last>130</last></pages><genre><json:string>journal</json:string></genre><subject><json:item><value>Regular Articles</value></json:item></subject></host><namedEntities><unitex><date><json:string>1000</json:string><json:string>2008</json:string></date><geogName><json:string>United States</json:string><json:string>Tennessee River</json:string></geogName><orgName><json:string>Board on Earth Sciences and Resources</json:string><json:string>North Carolina Wildlife Resources Commission, Raleigh, North Carolina</json:string><json:string>Columbia University</json:string><json:string>University of Tennessee Press</json:string><json:string>Princeton University</json:string><json:string>Stanford University</json:string><json:string>Cambridge University</json:string><json:string>National Academy Press, Washington, DC</json:string><json:string>University of Texas</json:string><json:string>Finnish Academy Postdoctoral Research Grant</json:string><json:string>Board Can</json:string><json:string>China and Vietnam</json:string><json:string>National Center for Biotechnology Information</json:string><json:string>North American Ichthyofauna and Bullhead</json:string><json:string>Oxford University</json:string><json:string>Division of Inland Fisheries</json:string></orgName><orgName_funder></orgName_funder><orgName_provider></orgName_provider><persName><json:string>W. 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Life Sciences</json:string><json:string>2 - Biochemistry, Genetics and Molecular Biology</json:string><json:string>3 - Genetics</json:string><json:string>1 - Life Sciences</json:string><json:string>2 - Agricultural and Biological Sciences</json:string><json:string>3 - Ecology, Evolution, Behavior and Systematics</json:string></scopus><inist><json:string>sciences appliquees, technologies et medecines</json:string><json:string>sciences biologiques et medicales</json:string><json:string>sciences biologiques fondamentales et appliquees. psychologie</json:string><json:string>invertebres</json:string></inist></categories><publicationDate>2008</publicationDate><copyrightDate>2008</copyrightDate><doi><json:string>10.1080/10635150801902193</json:string></doi><id>7BB9A3067B7287CA2E8CEB47C586DFE0C34B3A42</id><score>1</score><fulltext><json:item><extension>pdf</extension><original>true</original><mimetype>application/pdf</mimetype><uri>https://api.istex.fr/document/7BB9A3067B7287CA2E8CEB47C586DFE0C34B3A42/fulltext/pdf</uri></json:item><json:item><extension>zip</extension><original>false</original><mimetype>application/zip</mimetype><uri>https://api.istex.fr/document/7BB9A3067B7287CA2E8CEB47C586DFE0C34B3A42/fulltext/zip</uri></json:item><istex:fulltextTEI uri="https://api.istex.fr/document/7BB9A3067B7287CA2E8CEB47C586DFE0C34B3A42/fulltext/tei"><teiHeader><fileDesc><titleStmt><title level="a">The Relative Importance of Body Size and Paleoclimatic Change as Explanatory Variables Influencing Lineage Diversification Rate: An Evolutionary Analysis of Bullhead Catfishes (Siluriformes: Ictaluridae)</title></titleStmt><publicationStmt><authority>ISTEX</authority><publisher scheme="https://publisher-list.data.istex.fr">Taylor & Francis</publisher><availability><licence><p>© 2008 Society of Systematic Biologists</p></licence><p scheme="https://loaded-corpus.data.istex.fr/ark:/67375/XBH-GTWS0RDP-M">oup</p></availability><date>2008</date></publicationStmt><notesStmt><note type="research-article" scheme="https://content-type.data.istex.fr/ark:/67375/XTP-1JC4F85T-7">research-article</note><note type="journal" scheme="https://publication-type.data.istex.fr/ark:/67375/JMC-0GLKJH51-B">journal</note></notesStmt><sourceDesc><biblStruct type="inbook"><analytic><title level="a">The Relative Importance of Body Size and Paleoclimatic Change as Explanatory Variables Influencing Lineage Diversification Rate: An Evolutionary Analysis of Bullhead Catfishes (Siluriformes: Ictaluridae)</title><author xml:id="author-0000"><persName><forename type="first">Michael</forename><surname>Hardman</surname></persName><email>m.hardman@mac.com</email><affiliation>Laboratory of Molecular Systematics, Finnish Forest Research Institute, Jokiniemenkuja 1, 01301, Vantaa, Finland</affiliation></author><author xml:id="author-0001"><persName><forename type="first">Lotta M.</forename><surname>Hardman</surname></persName><email>m.hardman@mac.com</email><affiliation>Laboratory of Molecular Systematics, Finnish Forest Research Institute, Jokiniemenkuja 1, 01301, Vantaa, Finland</affiliation></author><editor xml:id="author-0002"><persName><forename type="first">Allan</forename><surname>Baker</surname></persName><email>m.hardman@mac.com</email><affiliation>Laboratory of Molecular Systematics, Finnish Forest Research Institute, Jokiniemenkuja 1, 01301, Vantaa, Finland</affiliation></editor><idno type="istex">7BB9A3067B7287CA2E8CEB47C586DFE0C34B3A42</idno><idno type="ark">ark:/67375/HXZ-F7LCQR6L-3</idno><idno type="DOI">10.1080/10635150801902193</idno></analytic><monogr><title level="j">Systematic Biology</title><idno type="pISSN">1063-5157</idno><idno type="eISSN">1076-836X</idno><idno type="publisher-id">sysbio</idno><idno type="PublisherID-hwp">sysbio</idno><imprint><publisher>Taylor & Francis</publisher><date type="published" when="2008-02"></date><biblScope unit="volume">57</biblScope><biblScope unit="issue">1</biblScope><biblScope unit="page" from="116">116</biblScope><biblScope unit="page" to="130">130</biblScope></imprint></monogr></biblStruct></sourceDesc></fileDesc><profileDesc><creation><date>2008</date></creation><abstract><p>We applied Bayesian phylogenetics, divergence time estimation, diversification pattern analysis, and parsimony-based methods of ancestral state reconstruction to a combination of nucleotide sequences, maximum body sizes, fossils, and paleoclimate data to explore the influence of an extrinsic (climate change) and an intrinsic (maximum body size) factor on diversification rates in a North American clade of catfishes (Ictaluridae). We found diversification rate to have been significantly variable over time, with significant (or nearly significant) rate increases in the early history of Noturus. Though the latter coincided closely with a period of dramatic climate change at the Eocene-Oligocene boundary, we did not detect evidence for a general association between climate change and diversification rate during the entire history of Ictaluridae. Within Ictaluridae, small body size was found to be a near significant predictor of species richness. Morphological stasis of several species appears to be a consequence of a homoplastic increase in body size. We estimated the maximum standard length of the ictalurid ancestor to be approximately 50 cm, comparable to Eocene ictalurids (Astephus) and similar to modern sizes of Ameiurus and their Asian sister-taxon Cranoglanis. During the late Paleocene and early Eocene, the ictalurid ancestor diversified into the lineages represented by the modern epigean genera. The majority of modern species originated in the Oligocene and Miocene, most likely according to a peripheral isolates model of speciation. We discuss the difficulties of detecting macroevolutionary patterns within a lineage history and encourage the scrutiny of the terminal Eocene climatic event as a direct promoter of diversification.</p></abstract><textClass><keywords scheme="keyword"><list><head>kwd</head><item><term>Clade assymmetry</term></item><item><term>Eocene extinction</term></item><item><term>historical biogeography</term></item><item><term>North American ichthyofauna</term></item><item><term>relaxed clock</term></item><item><term>speciation</term></item><item><term>Cenozoic freshwater fishes</term></item></list></keywords></textClass><textClass><keywords scheme="Journal Subject"><list><head></head><item><term>Regular Articles</term></item></list></keywords></textClass></profileDesc><revisionDesc><change when="2008-02">Published</change></revisionDesc></teiHeader></istex:fulltextTEI><json:item><extension>txt</extension><original>false</original><mimetype>text/plain</mimetype><uri>https://api.istex.fr/document/7BB9A3067B7287CA2E8CEB47C586DFE0C34B3A42/fulltext/txt</uri></json:item></fulltext><metadata><istex:metadataXml wicri:clean="corpus oup, element #text not found" wicri:toSee="no header"><istex:docType PUBLIC="-//NLM//DTD Journal Publishing DTD v2.3 20070202//EN" URI="journalpublishing.dtd" name="istex:docType"></istex:docType><istex:document><article article-type="research-article">
<front>
<journal-meta>
<journal-id journal-id-type="hwp">sysbio</journal-id>
<journal-id journal-id-type="publisher-id">sysbio</journal-id>
<journal-title>Systematic Biology</journal-title>
<issn pub-type="ppub">1063-5157</issn>
<issn pub-type="epub">1076-836X</issn>
<publisher>
<publisher-name>Taylor & Francis</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.1080/10635150801902193</article-id>
<article-categories>
<subj-group>
<subject>Regular Articles</subject>
</subj-group>
</article-categories>
<title-group>
<article-title>The Relative Importance of Body Size and Paleoclimatic Change as Explanatory Variables Influencing Lineage Diversification Rate: An Evolutionary Analysis of Bullhead Catfishes (Siluriformes: Ictaluridae)</article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name><surname>Hardman</surname><given-names>Michael</given-names></name>
</contrib>
<contrib contrib-type="author">
<name><surname>Hardman</surname><given-names>Lotta M.</given-names></name>
</contrib>
<contrib contrib-type="editor">
<name><surname>Baker</surname><given-names>Allan</given-names></name>
</contrib>
<aff><institution>Laboratory of Molecular Systematics, Finnish Forest Research Institute</institution> <addr-line>Jokiniemenkuja 1, 01301, Vantaa, Finland</addr-line>; E-mail: <email>m.hardman@mac.com</email> (M.H.)</aff>
</contrib-group>
<pub-date pub-type="ppub">
<month>2</month>
<year>2008</year>
</pub-date>
<volume>57</volume>
<issue>1</issue>
<fpage>116</fpage>
<lpage>130</lpage>
<history>
<date date-type="received">
<day>28</day>
<month>5</month>
<year>2007</year>
</date>
<date date-type="rev-recd">
<day>16</day>
<month>8</month>
<year>2007</year>
</date>
<date date-type="accepted">
<day>14</day>
<month>11</month>
<year>2007</year>
</date>
</history>
<copyright-statement>© 2008 Society of Systematic Biologists</copyright-statement>
<copyright-year>2008</copyright-year>
<abstract>
<p>We applied Bayesian phylogenetics, divergence time estimation, diversification pattern analysis, and parsimony-based methods of ancestral state reconstruction to a combination of nucleotide sequences, maximum body sizes, fossils, and paleoclimate data to explore the influence of an extrinsic (climate change) and an intrinsic (maximum body size) factor on diversification rates in a North American clade of catfishes (Ictaluridae). We found diversification rate to have been significantly variable over time, with significant (or nearly significant) rate increases in the early history of <italic>Noturus</italic>. Though the latter coincided closely with a period of dramatic climate change at the Eocene-Oligocene boundary, we did not detect evidence for a general association between climate change and diversification rate during the entire history of Ictaluridae. Within Ictaluridae, small body size was found to be a near significant predictor of species richness. Morphological stasis of several species appears to be a consequence of a homoplastic increase in body size. We estimated the maximum standard length of the ictalurid ancestor to be approximately 50 cm, comparable to Eocene ictalurids (<italic>Astephus</italic>) and similar to modern sizes of <italic>Ameiurus</italic> and their Asian sister-taxon <italic>Cranoglanis</italic>. During the late Paleocene and early Eocene, the ictalurid ancestor diversified into the lineages represented by the modern epigean genera. The majority of modern species originated in the Oligocene and Miocene, most likely according to a peripheral isolates model of speciation. We discuss the difficulties of detecting macroevolutionary patterns within a lineage history and encourage the scrutiny of the terminal Eocene climatic event as a direct promoter of diversification.</p>
</abstract>
<kwd-group kwd-group-type="kwd">
<kwd>Clade assymmetry</kwd>
<kwd>Eocene extinction</kwd>
<kwd>historical biogeography</kwd>
<kwd>North American ichthyofauna</kwd>
<kwd>relaxed clock</kwd>
<kwd>speciation</kwd>
<kwd>Cenozoic freshwater fishes</kwd>
</kwd-group>
</article-meta>
</front>
<body>
<p>Evolutionary biology aims to understand the factors that influence diversity and its distribution through space and time. Much of this understanding is sought through the identification of extrinsic factors in the environment, intrinsic factors of and among organisms, and the interaction of these factors through time (e.g., <xref ref-type="bibr" rid="b27">Futuyma, 1998</xref>; <xref ref-type="bibr" rid="b7">Brock, 2000</xref>). As might be expected, the influence and interaction of extrinsic and intrinsic factors varies among lineages and is not easily determined without a comprehensive evolutionary analysis (<xref ref-type="bibr" rid="b40">Harvey and Pagel, 1991</xref>).</p>
<p>Although pervasive extrinsic factors such as climate change and continental drift affect biotic systems broadly, component lineages can respond differently to a common stimulus (<xref ref-type="bibr" rid="b83">Prothero and Berggren, 1992</xref>; <xref ref-type="bibr" rid="b6">Bradshaw and Holzapfel, 2006</xref>). Intrinsic factors such as body size and thermal tolerance have been the focus of explanations for general trends observed in the spatial and temporal distribution of vertebrate phenotypes (<xref ref-type="bibr" rid="b2">Allen, 1877</xref>; <xref ref-type="bibr" rid="b4">Bergmann, 1847</xref>; <xref ref-type="bibr" rid="b12">Cope, 1887</xref>; <xref ref-type="bibr" rid="b31">Gloger, 1833</xref>). Recent studies using phylogenetically corrected tests describe both general (<xref ref-type="bibr" rid="b45">Knouft and Page, 2003</xref>) and lineage-specific (<xref ref-type="bibr" rid="b25">Finarelli and Flynn, 2006</xref>) evolutionary responses among North American freshwater fishes and caniform mammals, respectively. Of the intrinsic factors, maximum body size is believed to be the most important (<xref ref-type="bibr" rid="b81">Peters, 1983</xref>; <xref ref-type="bibr" rid="b94">Schmidt-Nielsen, 1984</xref>). However, the relative importance of intrinsic and extrinsic factors as drivers of diversification is poorly explored other than for some recent studies of insect-plant interactions (<xref ref-type="bibr" rid="b26">Forest et al., 2007</xref>) and flowering plants (<xref ref-type="bibr" rid="b63">Moore and Donoghue, 2007</xref>).</p>
<sec><title></title>
<sec><title>The North American Ichthyofauna and Bullhead Catfishes (Ictaluridae)</title>
<p>The North American freshwater ichthyofauna is a model system for the study of patterns and processes of diversification (Patterson, 1981; <xref ref-type="bibr" rid="b111">Wiley and Mayden, 1985</xref>; <xref ref-type="bibr" rid="b57">Mayden, 1987</xref>, <xref ref-type="bibr" rid="b58">1988</xref>). The fauna contains contemporary representatives of early actinopterygian lineages (e.g., <italic>Acipenser, Polyodon, Amia,</italic> and <italic>Lepisosteus</italic>) as well as descendants of all the freshwater teleost clades (osteoglossomorphs, elopomorphs, clupeomorphs, ostariophysans, protacanthopterygians, paracanthopterygians and acanthopterygians; <xref ref-type="bibr" rid="b48">Lee et al., 1980</xref>; <xref ref-type="bibr" rid="b70">Page and Burr, 1991</xref>). Of the endemic lineages, bullhead catfishes (Ictaluridae) are the most species rich.</p>
<p>A recent review of catfish nomenclature considered there to be seven ictalurid genera containing 64 extant species and a single genus containing 14 species represented by their fossilized remains (<xref ref-type="bibr" rid="b24">Ferraris, 2007</xref>). <xref ref-type="bibr" rid="b21">Egge and Simons (2006)</xref> described <italic>Noturus maydeni</italic> on the basis of its geographic separation and distinctive mitochondrial DNA, bringing the total of the most species-rich genus in the family to 29 binominals and with at least one species in the Carolinas awaiting description (<xref ref-type="bibr" rid="b70">Page and Burr, 1991</xref>; <xref ref-type="bibr" rid="b35">Hardman, 2004</xref>). According to <xref ref-type="bibr" rid="b24">Ferraris (2007)</xref>, <italic>Ameiurus</italic> is represented by seven extant and eight fossil species from Oligocene to Pleistocene deposits in western North America, and <italic>Ictalurus</italic> contains nine extant and four fossil species. However, J. G. Lundberg (personal communication) considers there to be an additional one to four Mexican species awaiting description, <italic>I. ochoterenai</italic> to be a synonym of <italic>I. dugesi</italic>, and <italic>I. meridionalis</italic> to be a distinct species rather than a synonym of <italic>I. furcatus</italic>. <italic>Pylodictis olivaris</italic> is the sole representative of the genus and known from Miocene fossils. No fossil material is known of the cave-dwelling <italic>Prietella</italic> (two species), <italic>Satan eurystomus</italic> or <italic>Trogloglanis pattersoni</italic>. Fossil ictalurids are known only from North America, though the family has a sister taxon found today in southern China and Vietnam (Cranoglanididae: <xref ref-type="bibr" rid="b17">Diogo, 2004</xref>; <xref ref-type="bibr" rid="b79">Peng et al. 2005</xref>; <xref ref-type="bibr" rid="b36">Hardman, 2005</xref>; <xref ref-type="bibr" rid="b98">Sullivan et al., 2006</xref>).</p>
<p>Other than the claims made by <xref ref-type="bibr" rid="b56">Matsuo et al. (2001)</xref>, ictalurid monophyly is undisputed (<xref ref-type="bibr" rid="b100">Taylor, 1969</xref>; <xref ref-type="bibr" rid="b49">Lundberg, 1975</xref>, 1985, <xref ref-type="bibr" rid="b51">1992</xref>; <xref ref-type="bibr" rid="b60">Mo, 1991</xref>; <xref ref-type="bibr" rid="b16">De Pinna, 1998</xref>; <xref ref-type="bibr" rid="b17">Diogo, 2004</xref>; <xref ref-type="bibr" rid="b35">Hardman, 2004</xref>, <xref ref-type="bibr" rid="b36">2005</xref>; <xref ref-type="bibr" rid="b98">Sullivan et al., 2006</xref>). Recent molecular phylogenetic studies concerning or including representatives of the family (<xref ref-type="bibr" rid="b37">Hardman and Page, 2003</xref>; <xref ref-type="bibr" rid="b35">Hardman, 2004</xref>; <xref ref-type="bibr" rid="b110">Wilcox et al., 2004</xref>; <xref ref-type="bibr" rid="b65">Near and Hardman, 2006</xref>; <xref ref-type="bibr" rid="b98">Sullivan et al., 2006</xref>; <xref ref-type="bibr" rid="b21">Egge and Simons, 2006</xref>) have collectively compiled a nearly complete taxon sample for mitochondrial gene cytochrome <italic>b</italic> (<italic>cytb</italic>) and the second subunit of the nuclear recombination activating gene (<italic>rag2</italic>). At the time of this study, sequences of both <italic>cytb</italic> and <italic>rag2</italic> were unavailable for the southwestern species of <italic>Ictalurus</italic> (<italic>I. australis, I. balsanus, I. dugesi, I. meridionalis, I. mexicanus,</italic> and <italic>I. pricei</italic>) and the four cave-dwelling taxa.</p>
<p>Lundberg (<xref ref-type="bibr" rid="b49">1975</xref>, <xref ref-type="bibr" rid="b51">1992</xref>) reviewed the fossil record of Ictaluridae. Though lacking the skull roof synapomorphies of the extant genera, fragments of an undetermined species of <italic>Astephus</italic> from late Paleocene-Eocene deposits of Wyoming provide a minimum age for the family of approximately 58 Ma. The extinct <italic>Ameiurus pectinatus</italic>, from Florissant lake deposits (Eocene-Oligocene boundary) in Colorado, provides a minimum age for <italic>Ameiurus</italic> of approximately 35 Ma. The oldest fossils of <italic>Ictalurus</italic> are Eocene-Oligocene and from the Cypress Hills Formation in Saskatchewan. The extant <italic>Ictalurus punctatus</italic> and <italic>Pylodictis olivaris</italic> are known to have existed at least as far back as the middle Miocene, as fossils identified as these species have been found in beds of South Dakota and Nebraska, respectively. Pleistocene <italic>Noturus</italic> are known from South Dakota.</p>
<p>Given the nearly complete taxon sample of ictalurids for mitochondrial and nuclear sequence data (<xref ref-type="bibr" rid="b37">Hardman and Page, 2003</xref>; <xref ref-type="bibr" rid="b35">Hardman, 2004</xref>; <xref ref-type="bibr" rid="b110">Wilcox et al., 2004</xref>; <xref ref-type="bibr" rid="b65">Near and Hardman, 2006</xref>; <xref ref-type="bibr" rid="b98">Sullivan et al., 2006</xref>; <xref ref-type="bibr" rid="b21">Egge and Simons, 2006</xref>), ample information concerning their biology, distribution, and systematics (<xref ref-type="bibr" rid="b100">Taylor, 1969</xref>; <xref ref-type="bibr" rid="b48">Lee, et al., 1980</xref>; <xref ref-type="bibr" rid="b70">Page and Burr, 1991</xref>) and representation in the fossil record (<xref ref-type="bibr" rid="b49">Lundberg, 1975</xref>, <xref ref-type="bibr" rid="b51">1992</xref>), the family is an attractive candidate for an analysis of the possible roles played by an extrinsic factor (climate change) and an intrinsic factor (maximum body size) on their diversification using parametric methods.</p>
</sec>
<sec><title>Evolutionary Analysis</title>
<p>Methodological developments in ancestral state reconstruction (<xref ref-type="bibr" rid="b39">Harvey et al., 1994</xref>; <xref ref-type="bibr" rid="b67">Nee et al., 1994</xref>; <xref ref-type="bibr" rid="b13">Cunningham et al., 1998</xref>; Oakley and Cunningham, 2002; <xref ref-type="bibr" rid="b68">Oakley, 2003</xref>; <xref ref-type="bibr" rid="b74">Pagel et al., 2004</xref>), divergence time estimation (<xref ref-type="bibr" rid="b18">Drummond et al., 2006</xref>; <xref ref-type="bibr" rid="b91">Sanderson, 1998</xref>, <xref ref-type="bibr" rid="b92">2002</xref>; <xref ref-type="bibr" rid="b105">Thorne et al., 1998</xref>; <xref ref-type="bibr" rid="b14">Cutler, 2000</xref>; <xref ref-type="bibr" rid="b44">Kishino et al., 2001</xref>; <xref ref-type="bibr" rid="b103">Thorne and Kishino, 2002</xref>, <xref ref-type="bibr" rid="b104">2005</xref>; <xref ref-type="bibr" rid="b113">Yang and Yoder, 2003</xref>), and diversification pattern analysis (<xref ref-type="bibr" rid="b10">Chan and Moore, 2002</xref>; <xref ref-type="bibr" rid="b39">Harvey et al., 1994</xref>; <xref ref-type="bibr" rid="b62">Moore et al., 2004</xref>; <xref ref-type="bibr" rid="b61">Moore and Chan, 2005</xref>; <xref ref-type="bibr" rid="b63">Moore and Donoghue, 2007</xref>; <xref ref-type="bibr" rid="b67">Nee et al., 1994</xref>, <xref ref-type="bibr" rid="b66">1996</xref>; <xref ref-type="bibr" rid="b75">Paradis, 1997</xref>, <xref ref-type="bibr" rid="b76">1998</xref>, <xref ref-type="bibr" rid="b77">2004</xref>) offer a toolbox with which to obtain statistically robust estimates of ancestral values and their errors. These parametric approaches integrate the uncertainty associated with estimates of phylogeny, branch lengths, fossil ages, and the temporal fluctuation in rates of speciation, extinction, nucleotide substitution, and morphological change to reconstruct evolutionary history and test hypotheses in a statistical framework.</p>
<p>By accommodating rate heterogeneity and fossil or paleogeographic calibration points in their maximum likelihood (ML) or Bayesian inferences, recent studies have been able to test and develop scenarios of diversification for brachyceran flies (<xref ref-type="bibr" rid="b109">Wiegmann et al., 2003</xref>), extinct moas (<xref ref-type="bibr" rid="b3">Baker et al., 2005</xref>), Neotropical placental mammals (<xref ref-type="bibr" rid="b15">Delsuc et al., 2004</xref>), modern bird orders in the late Cretaceous (<xref ref-type="bibr" rid="b80">Pereira and Baker 2006</xref>; <xref ref-type="bibr" rid="b96">Slack et al., 2006</xref>), and insect-plant interactions (<xref ref-type="bibr" rid="b26">Forest et al., 2007</xref>), as well as to determine the influence of dispersal and phenotypic innovations on diversification rates in flowering plants (<xref ref-type="bibr" rid="b63">Moore and Donoghue, 2007</xref>) and to explore biotic connections shown by catfishes found today in rivers of southern Mexico and tropical Africa (<xref ref-type="bibr" rid="b52">Lundberg et al., 2007</xref>). To this list, we add Bullhead catfishes as the focus of an examination of the respective roles played by Cenozoic climate change and maximum body size on diversification rate.</p>
<p>Briefly, the objectives of this study were to employ probabilistic methods of phylogenetic analysis, divergence time estimation, and ancestral state reconstruction to examine the possible relationships between changes in diversification rate, ancestral maximum body length, and paleoclimate during the evolutionary history of modern ictalurids. To meet these objectives, we used mitochondrial and nuclear protein coding sequences, several fossil calibration points, estimates of maximum body size from the literature, and a Cenozoic paleoclimate reconstruction based on oxygen isotope data from deep-sea cores (<xref ref-type="bibr" rid="b114">Zachos et al., 2001</xref>).</p>
</sec>
</sec>
<sec sec-type="methods"><title>Materials and Methods</title>
<sec><title>Taxon Sampling</title>
<p>We assembled <italic>cytb</italic> and <italic>rag2</italic> sequences (<xref ref-type="table" rid="tbl1">Table 1</xref>) deposited at the National Center for Biotechnology Information by <xref ref-type="bibr" rid="b37">Hardman and Page (2003)</xref>, <xref ref-type="bibr" rid="b35">Hardman (2004)</xref>, <xref ref-type="bibr" rid="b106">Waldbieser et al. (2003)</xref>, <xref ref-type="bibr" rid="b110">Wilcox et al. (2004)</xref>, <xref ref-type="bibr" rid="b79">Peng et al. (2005)</xref>, and <xref ref-type="bibr" rid="b98">Sullivan et al. (2006)</xref>, aligned them with Clustal X (<xref ref-type="bibr" rid="b102">Thompson et al., 1997</xref>), and checked for unexpected stop codons in MacClade (v.4.0; <xref ref-type="bibr" rid="b53">Maddison and Maddison, 2000</xref>) using appropriate translation codes. The data set includes the monotypic <italic>Pylodictis olivaris</italic>, all species of <italic>Ameiurus</italic>, all extant species of <italic>Noturus</italic> except <italic>N. crypticus, N. gladiator,</italic> and <italic>N. stanauli,</italic> and three of nine <italic>Ictalurus</italic> species. Following the results of <xref ref-type="bibr" rid="b17">Diogo (2004)</xref>, <xref ref-type="bibr" rid="b36">Hardman (2005)</xref>, <xref ref-type="bibr" rid="b79">Peng et al. (2005)</xref>, and <xref ref-type="bibr" rid="b98">Sullivan et al. (2006)</xref>, we used <italic>Cranoglanis bouderius</italic> (Cranoglanididae) as a proximal outgroup. The sequence alignment is available at <ext-link ext-link-type="uri" xlink:href="http://www.systematicbiology.org">http://www.systematicbiology.org</ext-link>.</p>
<table-wrap id="tbl1">
<label>Table 1</label>
<caption><p>Species, GenBank accession numbers, and source of sequence data. <sup><italic>a</italic></sup><xref ref-type="bibr" rid="b78">Peng et al. (2002)</xref>; <sup><italic>b</italic></sup><xref ref-type="bibr" rid="b98">Sullivan et al. (2006)</xref>; <sup><italic>c</italic></sup><xref ref-type="bibr" rid="b37">Hardman and Page (2003)</xref>; <sup><italic>d</italic></sup><xref ref-type="bibr" rid="b106">Waldbieser et al. (2003)</xref>; <sup><italic>e</italic></sup><xref ref-type="bibr" rid="b35">Hardman (2004)</xref>; <sup><italic>f</italic></sup><xref ref-type="bibr" rid="b110">Wilcox et al. (2004)</xref>.</p></caption>
<table frame="hsides" rules="groups">
<thead>
<tr>
<th align="left">Species</th>
<th align="center">cytb</th>
<th align="center">rag2</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left"><italic>Cranoglanis bouderius</italic></td>
<td align="center">AF416879<sup><italic>a</italic></sup></td>
<td align="center">DQ492401<sup><italic>b</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Ameiurus brunneus</italic></td>
<td align="center">AY184260<sup><italic>c</italic></sup></td>
<td align="center">AY184251<sup><italic>c</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Ameiurus catus</italic></td>
<td align="center">AY184267<sup><italic>c</italic></sup></td>
<td align="center">AY184249<sup><italic>c</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Ameiurus melas</italic></td>
<td align="center">AY184263<sup><italic>c</italic></sup></td>
<td align="center">AY184252<sup><italic>c</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Ameiurus natalis</italic></td>
<td align="center">AY184255<sup><italic>c</italic></sup></td>
<td align="center">AY184248<sup><italic>c</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Ameiurus nebulosus</italic></td>
<td align="center">AY184257<sup><italic>c</italic></sup></td>
<td align="center">AY184250<sup><italic>c</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Ameiurus platycephalus</italic></td>
<td align="center">AY184259<sup><italic>c</italic></sup></td>
<td align="center">AY184247<sup><italic>c</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Ameiurus serracanthus</italic></td>
<td align="center">AY184256<sup><italic>c</italic></sup></td>
<td align="center">AY184246<sup><italic>c</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Ictalurus furcatus</italic></td>
<td align="center">AF484159<sup><italic>d</italic></sup></td>
<td align="center">AY327075<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Ictalurus lupus</italic></td>
<td align="center">AY327267<sup><italic>e</italic></sup></td>
<td align="center">AY327076<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Ictalurus punctatus</italic></td>
<td align="center">AY184253<sup><italic>c</italic></sup></td>
<td align="center">AY184245<sup><italic>c</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus albater</italic></td>
<td align="center">AY327268<sup><italic>e</italic></sup></td>
<td align="center">AY327077<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus baileyi</italic></td>
<td align="center">AY327272<sup><italic>e</italic></sup></td>
<td align="center">AY327079<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus elegans</italic></td>
<td align="center">AY327274<sup><italic>e</italic></sup></td>
<td align="center">AY327080<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus eleutherus</italic></td>
<td align="center">AY327278<sup><italic>e</italic></sup></td>
<td align="center">AY327082<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus exilis</italic></td>
<td align="center">AY327280<sup><italic>e</italic></sup></td>
<td align="center">AY327083<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus fasciatus</italic></td>
<td align="center">AY327276<sup><italic>e</italic></sup></td>
<td align="center">AY327081<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus flavater</italic></td>
<td align="center">AY327283<sup><italic>e</italic></sup></td>
<td align="center">AY327084<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus flavipinnis</italic></td>
<td align="center">AY327284<sup><italic>e</italic></sup></td>
<td align="center">AY327085<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus flavus</italic></td>
<td align="center">AY327288<sup><italic>e</italic></sup></td>
<td align="center">AY327086<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus funebris</italic></td>
<td align="center">AY327291<sup><italic>e</italic></sup></td>
<td align="center">AY327087<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus furiosus</italic></td>
<td align="center">AY327292<sup><italic>e</italic></sup></td>
<td align="center">AY327088<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus gilberti</italic></td>
<td align="center">AY327294<sup><italic>e</italic></sup></td>
<td align="center">AY327089<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus gyrinus</italic></td>
<td align="center">AY327295<sup><italic>e</italic></sup></td>
<td align="center">AY327090<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus hildebrandi</italic></td>
<td align="center">AY327298<sup><italic>e</italic></sup></td>
<td align="center">AY327091<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus insignis</italic></td>
<td align="center">AY327301<sup><italic>e</italic></sup></td>
<td align="center">AY327092<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus lachneri</italic></td>
<td align="center">AY327304<sup><italic>e</italic></sup></td>
<td align="center">AY327093<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus leptacanthus</italic></td>
<td align="center">AY327305<sup><italic>e</italic></sup></td>
<td align="center">AY327094<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus maydeni</italic></td>
<td align="center">AY327271<sup><italic>e</italic></sup></td>
<td align="center">AY327078<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus miurus</italic></td>
<td align="center">AY327306<sup><italic>e</italic></sup></td>
<td align="center">AY327095<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus munitus</italic></td>
<td align="center">AY327309<sup><italic>e</italic></sup></td>
<td align="center">AY327096<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus nocturnus</italic></td>
<td align="center">AY327311<sup><italic>e</italic></sup></td>
<td align="center">AY327097<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus phaeus</italic></td>
<td align="center">AY327315<sup><italic>e</italic></sup></td>
<td align="center">AY327098<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus placidus</italic></td>
<td align="center">AY327317<sup><italic>e</italic></sup></td>
<td align="center">AY327099<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus stigmosus</italic></td>
<td align="center">AY327319<sup><italic>e</italic></sup></td>
<td align="center">AY327100<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus taylori</italic></td>
<td align="center">AY327321<sup><italic>e</italic></sup></td>
<td align="center">AY327101<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Noturus</italic> sp.(broadtail)</td>
<td align="center">AY32732<sup><italic>e</italic></sup></td>
<td align="center">AY327102<sup><italic>e</italic></sup></td>
</tr>
<tr>
<td align="left"><italic>Pylodictis olivaris</italic></td>
<td align="center">AY458887<sup><italic>f</italic></sup></td>
<td align="center">AY327103<sup><italic>e</italic></sup></td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec><title>Phylogeny Estimation</title>
<p>The posterior probability distribution of tree topologies was estimated with the Metropolis-coupled Markov chain Monte Carlo (MC<sup>3</sup>) algorithm implemented in MrBayes (v3.1.2; <xref ref-type="bibr" rid="b42">Huelsenbeck and Ronquist, 2001</xref>; <xref ref-type="bibr" rid="b90">Ronquist and Huelsenbeck, 2003</xref>). Following the recommendations of Shapiro et al. (2006), codon models were applied to four partitions in the data: (1) first and second positions of <italic>cytb</italic>, (2) third positions of <italic>cytb</italic>, (3) first and second positions of <italic>rag2</italic>, and (4) third positions of <italic>rag2</italic>. ModelTest (v. 3.7; <xref ref-type="bibr" rid="b82">Posada and Crandall, 1998</xref>) identified the optimal model for each partition according to differences in the Akaike information criterion using parameter estimates and likelihood scores calculated by PAUP* (v.4.0b10; <xref ref-type="bibr" rid="b99">Swofford, 2001</xref>; <xref ref-type="table" rid="tbl2">Table 2</xref>). Given the available settings in MrBayes, a GTR substitution model was specified when ModelTest selected submodels of three or more substitution categories. All state frequencies, substitution rates, distributions of rate heterogeneity, and the proportion of invariant sites were sampled separately (when included in the model) for each data partition. All other priors were specified with default settings. Two independent runs of 1 × 10<sup>7</sup> generations were completed, each containing four chains (three heated incrementally with a temperature of 0.2) initiated from random starting trees and sampled every 1 × 10<sup>3</sup> generations. Upon completion of the runs, convergence to a stationary distribution was examined by referring to the average standard deviation of split frequencies between paired cold chains and time series plots of the tree scores (negative log likelihoods). The first 3000 samples (3 × 10<sup>6</sup> generations) were discarded as burn-in and the maximum clade credibility tree (MCC) calculated with TreeAnnotator (v1.4.5r516; Rambaut and Drummond, 2007). The MCC is preferred to the 50% majority consensus of post–burn-in samples as it represents the maximum product of posterior probabilities of any single tree visited during the MC<sup>3</sup> run. Branch support for nodes in the MCC was explored through reference to nonparametric bootstrap proportions obtained according to ML estimates using the GTR model applied across all sites combined in a single partition in GARLI (v0.95; <xref ref-type="bibr" rid="b116">Zwickl, 2006</xref>, at <ext-link ext-link-type="uri" xlink:href="http://www.bio.utexas.edu/faculty/antisense/garli/Garli.html">http://www.bio.utexas.edu/faculty/antisense/garli/Garli.html</ext-link>). Five hundred pseudoreplicates were completed, each starting from a random tree and terminating after 1 × 10<sup>5</sup> generations.</p>
<table-wrap id="tbl2">
<label>Table 2</label>
<caption><p>Optimal models identified according to differences in Akaike information criteria (Δ AIC) by ModelTest, their descriptions, and closest application in MrBayes as settings permit.</p></caption>
<table frame="hsides" rules="groups">
<thead>
<tr>
<th align="left">Data partition</th>
<th align="center">Optimal model</th>
<th align="center">Base frequencies</th>
<th align="center">Substitution classes</th>
<th align="center">MC<sup>3</sup> model</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left"><italic>cytb</italic> 1st and 2nd</td>
<td align="left">TVM+I+Γ</td>
<td align="left">Unequal</td>
<td align="left">4Tv, 1Ti</td>
<td align="left">GTR+I+Γ</td>
</tr>
<tr>
<td align="left"><italic>cytb</italic> 3rd</td>
<td align="left">GTR+I+Γ</td>
<td align="left">Unequal</td>
<td align="left">4Tv, 2Ti</td>
<td align="left">GTR+I+Γ</td>
</tr>
<tr>
<td align="left"><italic>rag2</italic> 1st and 2nd</td>
<td align="left">K80+Γ</td>
<td align="left">Equal</td>
<td align="left">1 (Ti:Tv)</td>
<td align="left">K80+Γ</td>
</tr>
<tr>
<td align="left"><italic>rag2</italic> 3rd</td>
<td align="left">TrN+Γ</td>
<td align="left">Unequal</td>
<td align="left">1Tv, 2Ti</td>
<td align="left">GTR+Γ</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec><title>Divergence Time Estimation</title>
<p>According to a likelihood-ratio test (LRT; <xref ref-type="bibr" rid="b47">Langley and Fitch, 1974</xref>) of the MCC and log-likelihood scores estimated by PAUP* (according to models specified by ModelTest for each partition in turn), the ictalurid data set was found to be overdispersed (2Δ lnL = 59.49–1136.91, <italic>df</italic> = 35, <italic>P</italic> < 0.001) with respect to a molecular clock. Given significant rate heterogeneity among lineages, the 95% highest posterior density (HPD) of divergence times was estimated with a relaxed-clock MCMC approach (<xref ref-type="bibr" rid="b19">Drummond et al., 2002</xref>) using the uncorrelated lognormal (UCLN) model (<xref ref-type="bibr" rid="b18">Drummond et al., 2006</xref>) implemented in BEAST (v.1.4.5; <xref ref-type="bibr" rid="b18">Drummond and Rambaut, 2006</xref>). Unlike other Bayesian divergence time estimators the UCLN model does not assume autocorrelation of substitution rates across nodes, though they are permitted. With respect to node age constraints and absolute rate calibration, we set conditional lognormal priors with means and standard deviations of 1.0 and offset values of 4.0, 19.0, 19.0, 35.0, and a root prior offset of 58.0 with mean and standard deviation of 1.1 (<xref ref-type="table" rid="tbl3">Table 3</xref>). Although other fossils are available, their morphological generality or distribution in time provide no further information concerning temporal constraints as they are either younger than the four informative fossils or unable to be placed phylogenetically.</p>
<table-wrap id="tbl3">
<label>Table 3</label>
<caption><p>Description and fossil basis of lognormal prior distributions of node age constraints specified in the BEAST MCMC analysis (MRCA = most recent common ancestor). All fossil identifications from <xref ref-type="bibr" rid="b49">Lundberg (1975</xref>, <xref ref-type="bibr" rid="b51">1992)</xref> and zero offsets based on stratigraphic ages from <xref ref-type="bibr" rid="b112">Woodburne (2004)</xref>.</p></caption>
<table frame="hsides" rules="groups">
<thead>
<tr>
<th align="left">Constrained node</th>
<th align="center">Zero offset</th>
<th align="center">Mean ± SD</th>
<th align="center">Fossil justification</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">MRCA: Ictaluridae (root node)</td>
<td align="center">58.0</td>
<td align="center">1.1 ± 1.1</td>
<td align="left">†<italic>Astephus</italic> sp.: Paleocene-Eocene</td>
</tr>
<tr>
<td align="left">MRCA: <italic>Ictalurus</italic> + <italic>Pylodictis + Noturus</italic></td>
<td align="center">35</td>
<td align="center">1.0 ± 1.0</td>
<td align="left">†<italic>Ictalurus rhaea</italic>s: Eocene-Oligocene †<italic>Ameiurus pectinatus</italic>: Eocene-Oligocene</td>
</tr>
<tr>
<td align="left">MRCA: <italic>Ictalurus</italic></td>
<td align="center">19</td>
<td align="center">1.0 ± 1.0</td>
<td align="left"><italic>Ictalurus punctatus</italic>: Miocene</td>
</tr>
<tr>
<td align="left">MRCA: <italic>Pylodictis</italic> + <italic>Noturus</italic></td>
<td align="center">19</td>
<td align="center">1.0 ± 1.0</td>
<td align="left"><italic>Pylodictis olivaris</italic>: Miocene</td>
</tr>
<tr>
<td align="left">MRCA: <italic>A. melas</italic> + <italic>A. nebulosus</italic></td>
<td align="center">4</td>
<td align="center">1.0 ± 1.0</td>
<td align="left">†<italic>Ameiurus sawrockensis</italic>: Pleistocene</td>
</tr>
</tbody>
</table>
</table-wrap>
<p>Two independent and identical BEAST analyses were completed, each of 1 × 10<sup>7</sup> generations during which the posterior probability density of divergence times was estimated with a UCLN relaxed clock modeling GTR+I+Γ. All parameters were unlinked and applied separately to both of two partitions: (1) all first- and second-codon positions combined, and (2) all third positions. The prior for the branching process was set according to a pure birth (Yule) model assuming a constant speciation rate per lineage. A starting chronogram that satisfied the node age priors was generated by first importing the MCC annotated with mean branch lengths from the MC<sup>3</sup> analysis into PAUP*, deleting the outgroup (<italic>Cranoglanis bouderius</italic>), resetting the root in its place, and enforcing the resulting phylogram and fossil calibrations described above in R8S (v. 1.71; <xref ref-type="bibr" rid="b93">Sanderson, 2003</xref>). The nonparametric rate smoothing (NPRS) method (powell algorithm, otherwise default settings) was used to estimate unknown node ages and provide an ultrametric tree. The resulting chronogram was checked in TreeEdit (v1.0a10; Rambaut and Charleston, 2002) to ensure node ages and clades were among those specified in the prior distributions of the BEAST MCMC analysis. This chronogram, in newick format, replaced the UPGMA starting tree in the BEAST input file and the pertinent text was edited appropriately.</p>
<p>Following completion of the runs, stationarity of each posterior distribution was examined according to the marginal probabilities of sampled parameters using Tracer (v1.3; Rambaut and Drummond, 2003). Given stationary parameter estimates and effective sample sizes (ESS) > 1000, samples from both runs were combined using LogCombiner and the MCC calculated in TreeAnnotator. Samples of the distribution taken prior to stationarity were discarded as burn-in. FigTree (v1.0; Rambaut, 2006) was used to visualize the chronogram and 95% HPD of divergence times.</p>
</sec>
<sec><title>Patterns and Rates of Lineage Diversification</title>
<p>Following Moore and Donoghue (2007), shifts in lineage diversification rate through time were evaluated using both temporal and topological approaches. Temporal methods involve the distribution of node ages through time and calculation of the relative cladogenesis statistic (<xref ref-type="bibr" rid="b66">Nee et al., 1996</xref>; <xref ref-type="bibr" rid="b63">Moore and Donoghue, 2007</xref>) in END-EPI (<xref ref-type="bibr" rid="b89">Rambaut et al., 1997</xref>). The topological method examined the MCC branching pattern and a sample of 1000 trees drawn from the stationary distribution of the MC<sup>3</sup> analysis for significant changes in diversification rate by calculating shift statistics (Δ <sub>1</sub>) and performing whole-tree tests of diversification rate variation using SymmeTREE (v1.1; Chan and Moore, 2005). The null distribution for each test statistic was generated by Monte Carlo simulation of 1 × 10<sup>6</sup> trees containing the same number of taxa as the test tree and branching according to an equal-rates Markov (ERM) model. In order to explore issues associated with taxon sampling in the diversification rate analysis (e.g., <xref ref-type="bibr" rid="b66">Nee et al., 1996</xref>), an experiment following that outlined by <xref ref-type="bibr" rid="b61">Moore and Chan (2005)</xref> and <xref ref-type="bibr" rid="b63">Moore and Donoghue (2007)</xref> was completed by assigning the missing extant species to their respective supraspecific taxa as far as they are known. The missing extant <italic>Ictalurus</italic> species were assigned according to the synthetic phylogeny of <xref ref-type="bibr" rid="b51">Lundberg (1992)</xref>; i.e., <italic>I. balsanus</italic> and <italic>I. meridionalis</italic> in a trichotomy along with <italic>I. furcatus</italic>; and <italic>I. australis</italic>, <italic>I. dugesi</italic> (including <italic>I. ochoterenai</italic>), <italic>I. mexicanus,</italic> and <italic>I. pricei</italic> in an unresolved node subtending these species as well as the sampled <italic>I. punctatus</italic> and <italic>I. lupus</italic>. Similarly, <italic>Noturus crypticus</italic> and <italic>N. stanauli</italic> were assigned to a polychotomous node subtending these two species; and <italic>N. baileyi, N. elegans, N. fasciatus, N. hildebrandi</italic>, and <italic>N. gladiator</italic> as sister to <italic>N. stigmosus</italic> following <xref ref-type="bibr" rid="b35">Hardman (2004)</xref>, <xref ref-type="bibr" rid="b65">Near and Hardman (2006)</xref>, and <xref ref-type="bibr" rid="b21">Egge and Simons (2006)</xref>. Soft polytomies were randomly resolved 1 × 10<sup>6</sup> times according to the taxon-size-sensitive ERM model (<xref ref-type="bibr" rid="b10">Chan and Moore, 2002</xref>; <xref ref-type="bibr" rid="b61">Moore and Chan, 2005</xref>).</p>
</sec>
<sec><title>Reconstruction of Ancestral Body Size and Its Correspondence to Species Richness</title>
<p>Body size has been identified as one of the most important intrinsic factors governing animal biology (<xref ref-type="bibr" rid="b94">Schmidt-Nielsen, 1984</xref>) and one that has exhibited directional evolutionary trends among families of North American freshwater fishes (<xref ref-type="bibr" rid="b45">Knouft and Page, 2003</xref>). The extant and reconstructed evolution of maximum standard length (MSL; body length excluding the caudal fin) was examined with respect to the MCC from the BEAST MCMC analysis and compared to the results of the diversification rate analysis and changes in Cenozoic climate. We collected MSLs from <xref ref-type="bibr" rid="b70">Page and Burr (1991)</xref>, <xref ref-type="bibr" rid="b101">Thomas and Burr (2004)</xref>, <xref ref-type="bibr" rid="b9">Burr et al. (2005)</xref>, and Egge and Simons (<xref ref-type="bibr" rid="b21">2006</xref>; see <xref ref-type="fig" rid="fig2">Fig. 2</xref>). These continuous data were natural-log–transformed prior to being analyzed according to MCMC methods in BayesTraits (<ext-link ext-link-type="uri" xlink:href="http://www.evolution.reading.ac.uk/">http://www.evolution.reading.ac.uk/</ext-link>; <xref ref-type="bibr" rid="b74">Pagel et al., 2004</xref>) and weighted-squared-change parsimony (WSP; <xref ref-type="bibr" rid="b54">Maddison, 1991</xref>) in Mesquite (v. 1.12; Maddison and Maddison, 2006). Additionally, MacroCAIC (v. 1.0.1; <xref ref-type="bibr" rid="b1">Agapow and Isaac, 2002</xref>) was used to evaluate the relationship between species richness and lnMSL through the comparison of independent contrasts (<xref ref-type="bibr" rid="b23">Felsenstein, 1985</xref>; <xref ref-type="bibr" rid="b40">Harvey and Pagel, 1991</xref>; <xref ref-type="bibr" rid="b28">Garland et al., 1992</xref>).</p>
<p>BayesTraits was used to examine the evolution of lnMSL across the post–burn-in phylograms from the MC<sup>3</sup> analysis. Prior to their input to BayesTraits, the sample of phylograms was thinned to 4.0 × 10<sup>3</sup> and rooted according to the outgroup (<italic>Cranoglanis bouderius</italic>) in Mesquite so that the ingroup node was dichotomous and the outgroup had a positive branch length. A total of 2 × 10<sup>7</sup> iterations, sampled every 1 × 10<sup>3</sup>, were completed and the number of generations required to reach stationarity of the posterior distribution detected by examining marginal probabilities plotted as time series in TRACER. The “ratedev” prior was set heuristically so that the mean acceptance of the proposed state was at least 25% in the posterior distribution. This parameter enables the chain to be effectively mixed when stationary. All other priors were uniformly distributed. Three replicate MCMC runs were completed to estimate the distribution of likelihood scores of nested hypotheses in which the lnMSL data evolved according to a random-walk or a directional model of evolution across the samples of MC<sup>3</sup> phylograms. Bayes factors (BFs) were used to assess relative support for the alternative (directional) and null (random-walk) hypotheses, calculated as twice the difference between the harmonic mean of the marginal log likelihood under the corresponding model (e.g., <xref ref-type="bibr" rid="b97">Suchard et al., 2001</xref>). The preferred evolutionary model was then used to estimate the mean values of posterior distributions of three scaling parameters: delta (δ; ancient or recent trait evolution), kappa (κ; rate heterogeneity in trait evolution), and lambda (λ; phylogenetic signal in trait evolution; Pagel, <xref ref-type="bibr" rid="b71">1994</xref>, <xref ref-type="bibr" rid="b72">1997</xref>, <xref ref-type="bibr" rid="b73">1999</xref>).</p>
<p>Unfortunately, BayesTraits can only reconstruct ancestral states for discretely coded data; e.g., binary or multistate. In its place, the WSP method was used to reconstruct ancestral states of lnMSL on the MCC in Mesquite. WSP minimizes the sum of squared changes occurring tip-to-node and node-to-node weighted according to their branch length (<xref ref-type="bibr" rid="b54">Maddison, 1991</xref>). By incorporating branch lengths, WSP mimics an ML estimate of the same assuming a Brownian motion evolutionary process (<xref ref-type="bibr" rid="b25">Finarelli and Flynn, 2006</xref>). Following the detection of significant phylogenetic structure (λ ≈ 1.0), the PDAP module (<xref ref-type="bibr" rid="b59">Midford et al., 2005</xref>) was used to estimate standard errors and confidence intervals for the ancestral lnMSLs following <xref ref-type="bibr" rid="b29">Garland et al. (1999)</xref>.</p>
<p>In order to evaluate the extent to which lnMSL predicts species richness among ictalurids, least-squares regression through the origin (<xref ref-type="bibr" rid="b28">Garland et al., 1992</xref>) of 24 independent contrasts (sister-species comparisons are uninformative) was completed in MacroCAIC using the MCC with branch lengths in units of time following the recommendations of <xref ref-type="bibr" rid="b43">Isaac et al. (2003)</xref>. Differences in clade species richness were measured according to the relative rate difference statistic (RRD = ln[<italic>n</italic><sub><italic>i</italic></sub>/<italic>n</italic><sub><italic>j</italic></sub>], where <italic>n</italic><sub><italic>i</italic></sub> is the number of species in the larger clade, and <italic>n</italic><sub><italic>j</italic></sub> the number in the smaller clade; <xref ref-type="bibr" rid="b30">Gittleman and Purvis, 1998</xref>; <xref ref-type="bibr" rid="b43">Isaac et al., 2003</xref>). The ancestral reconstruction of lnMSL was made according to a Brownian motion model of character change, as in WSP, with branch lengths taken between point estimates of node ages from the BEAST MCMC analysis. Similar to <xref ref-type="bibr" rid="b30">Gittleman and Purvis (1998)</xref>, the extent to which species richness was dependent on a particular value of lnMSL was tested by regressing RRD against reconstructed values of lnMSL. Also, to examine the extent to which the association was constant through time, RRD was regressed against node age.</p>
</sec>
<sec><title>Paleoclimatic Change and Its Relationship to Diversification Rate</title>
<p>To explore the correspondence of possible associations between changes in climate and natural log per lineage accumulation rate (lnλ) during the Cenozoic, mean ocean temperature (MOT) changes were collected from the paleoclimate reconstruction of <xref ref-type="bibr" rid="b114">Zachos et al. (2001)</xref> and changes in the lnλ from the MCMC chronogram for each of 58 one-million-year intervals. Given that the analysis does not include an estimate of the per lineage extinction rate, lnλ is based solely on lineage birth and thus assumes either positive (speciation) or neutral (no speciation) values. Changes in MOT on the other hand can be positive, neutral or negative. Observations of the six possible pairings were scored and exposed to a standard χ<sup>2</sup> test of the null hypothesis of no association between the change in MOT and change in lnλ. Additionally, the correspondence between these two variables based on the absolute rate of change in MOT (±°C per million years) was examined according to a two-tailed test using Kendall's τ<sub><italic>b</italic></sub> correlation coefficient.</p>
</sec>
</sec>
<sec><title>Results</title>
<sec><title>Phylogeny</title>
<p>After approximately 3 × 10<sup>6</sup> generations, the average standard deviation between split frequencies of the coupled runs stabilized with stochastic fluctuation between 0.0045 and 0.007, suggesting convergence to the stationary distribution. Accordingly, the first 3 × 10<sup>4</sup> samples were discarded as burn-in. All parameter estimates of the post burn-in sample had ESS values > 1000. The MCC of the MC<sup>3</sup> analysis was made ultrametric in r8s and specified as starting tree for the MCMC analysis in BEAST. Given the inclusion of additional prior information, i.e., node age distributions, the MCC obtained from the post–burn-in sample of the BEAST MCMC analysis was considered the best estimate of phylogeny. <xref ref-type="fig" rid="fig1">Figure 1</xref> displays the results of the divergence time reconstruction, and <xref ref-type="fig" rid="fig2">Fig. 2</xref> the cladogram containing node posterior probabilities (PPs) and proportion of 500 ML bootstrap pseudoreplicates (MLBPs) estimated by GARLI.</p>
<fig id="fig1">
<label>Figure 1</label><caption><p>Maximum credibility chronogram resulting from the combined samples of the stationary posterior distributions estimated in the BEAST MCMC analysis. Branch lengths are in units of time and error bars represent the 95% highest posterior densities. Nodes labeled with symbols were identified as the locations of significant (<italic>P</italic> < 0.05: filled circles and star) and nearly significant (<italic>P</italic> = 0.07: filled square and star) diversification rate shifts in END-EPI and SymmeTREE, respectively. Lower bounds for the five constrained nodes are labeled in Ma. Inset shows the plot of log lineage accumulation rate against the mean ocean temperature (climate) reconstruction of <xref ref-type="bibr" rid="b114">Zachos et al. (2001)</xref>. Image of <italic>Ictalurus furcatus</italic> reproduced from <xref ref-type="bibr" rid="b22">Etnier and Starnes (1993)</xref>.</p></caption>
<graphic xlink:href="57-1-116-f1.gif"></graphic>
</fig>
<fig id="fig2">
<label>Figure 2</label><caption><p>Cladogram corresponding to the maximum credibility tree resulting from the BEAST MCMC analysis with posterior probabilities displayed above branches and the proportion of 500 maximum likelihood bootstrap pseudoreplicates below (not shown if recovered in less than 0.50 of pseudoreplicates). Black silhouettes are scaled maximum standard lengths (MSLs) of the extant ictalurid fauna. Grey silhouettes are scaled point estimates of ancestral MSLs with 95% confidence intervals in the accompanying shaded boxes. Filled circles, square, and star correspond to the diversification rate shifts noted in <xref ref-type="fig" rid="fig1">Fig. 1</xref> and text.</p></caption>
<graphic xlink:href="57-1-116-f2.gif"></graphic>
</fig>
<p>In the MCC, all genera were recovered monophyletic with convincing support (PPs and MLBPs of 1.0 and 0.99 to 1.0, respectively). <italic>Ameiurus</italic> was resolved as the basal genus and <italic>Ictalurus</italic> as sister to <italic>Noturus</italic> and <italic>Pylodictis</italic>. Though intergeneric nodes all had PPs of 1.0, only the clade comprising <italic>Noturus</italic> and <italic>Pylodictis</italic> was found in more than 0.5 of MLBPs (0.72). Relationships among <italic>Ameiurus</italic> species were resolved as in <xref ref-type="bibr" rid="b37">Hardman and Page (2003)</xref> and relationships among the incompletely sampled <italic>Ictalurus</italic> were consistent with those of previous studies based on morphology (Lundberg, 1970, <xref ref-type="bibr" rid="b51">1992</xref>). <italic>Ictalurus furcatus</italic> was found to be sister to a clade of the widespread <italic>I. punctatus</italic> and the southwestern <italic>I. lupus</italic>. <italic>Pylodictis</italic> is monotypic and its recovery as sister to <italic>Noturus</italic> is consistent with the morphological studies of <xref ref-type="bibr" rid="b100">Taylor (1969)</xref> and Lundberg (<xref ref-type="bibr" rid="b49">1975</xref>, <xref ref-type="bibr" rid="b50">1982</xref>, <xref ref-type="bibr" rid="b51">1992</xref>). Relationships among <italic>Noturus</italic> species were similar to those inferred from analyses of similar data sets (<xref ref-type="bibr" rid="b35">Hardman, 2004</xref>; <xref ref-type="bibr" rid="b9">Burr et al., 2005</xref>; <xref ref-type="bibr" rid="b65">Near and Hardman, 2006</xref>; <xref ref-type="bibr" rid="b21">Egge and Simons, 2006</xref>) and a survey of allozyme and chromosomal variation (<xref ref-type="bibr" rid="b32">Grady and LeGrande, 1992</xref>).</p>
</sec>
<sec><title>Divergence Time Estimates</title>
<p>Stationarity of each of the BEAST MCMC posterior distributions was examined by plotting time series of the marginal probabilities of estimated parameters. Samples of the first 2.0 × 10<sup>6</sup> generations were discarded as burn-in and subsequent ESSs of all parameters were at least 1.3 × 10<sup>3</sup>. The MCC of combined samples with the stationary distribution is shown in <xref ref-type="fig" rid="fig1">Fig. 1</xref>. The mean ± standard deviation width of the 95% HPDs was 11.8 ± 4.7 Ma. Error widths were positively correlated with node age (B = 2.22, SE = 0.237, <italic>t</italic> = 9.38, <italic>P</italic> < 0.001); thus, more ancient nodes were less precisely estimated. Overall, the chronology describes a scenario in which the modern ictalurid lineages originated early in the Eocene and that the majority of extant species originated during the Oligocene and Miocene.</p>
</sec>
<sec><title>Lineage Diversification Rates</title>
<p>The temporal method employed in END-EPI identified four nodes in the MCC with significant rate increases (<italic>P</italic> < 0.05), all located in the early diversification of the <italic>Noturus</italic> lineage (<xref ref-type="fig" rid="fig1">Fig. 1</xref>). The topological method employed in SymmeTREE identified significant rate variation among lineages (<italic>P</italic> = 0.0002–0.002) and two near-significant rate shifts (<italic>P</italic> = 0.07) in the MCC, one of which was also identified by END-EPI. Summarized whole-tree rate variation tests based on 1 × 10<sup>4</sup> samples from the stationary distribution of the MC<sup>3</sup> analysis were of reduced significance (<italic>P</italic> = 0.07–0.03) with respect to the tests based on the MCC, though they similarly implied or identified significant diversification rate heterogeneity. Although test statistics increased slightly in significance, including the unsampled taxa did not affect the conclusions based on the original matrix and MCC. The taxon-inclusion experiment did however identify the node subtending all non-<italic>Ameiurus</italic> ictalurids as the location of a significant diversification rate shift (<italic>P</italic> = 0.03). This clade received all of the unsampled taxa in the experiment.</p>
</sec>
<sec><title>Reconstruction of lnMSL Evolution and Influence on Species Richness</title>
<p>Convergence of the MCMC analyses in BayesTraits was assessed by plotting the loglikelihood scores of each sampled generation as time series and discarding those beneath the asymptote (2.0 × 10<sup>6</sup> generations) as burn-in. The BF (= 3.62) obtained from the comparison of harmonic means of the marginal log likelihoods rejected the null hypothesis of a random walk in favor of a directional model of evolution. Under the directional model, mean ± standard deviations of the scaling parameters δ (0.88 ± 0.26), κ (0.70 ± 0.17), and λ (0.82 ± 0.10) suggested the majority of lnMSL evolution to have taken place early in the lineage history, to have remained fairly constant following those early changes, and to be structured phylogenetically. Collectively, these values describe a punctuated model of evolution for MSL in Ictaluridae.</p>
<p><xref ref-type="fig" rid="fig2">Figure 2</xref> shows scaled point estimates and 95% confidence intervals of the reconstructed ancestral MSLs. Based on the WSP analysis, the ancestral ictalurid had a mean MSL of 50.9 cm (with a 95% confidence interval of 27.8 to 93.1 cm), which is similar to the larger species of modern <italic>Ameiurus</italic>. Similar ancestral conditions were reconstructed for the common ancestors of the non-<italic>Ameiurus</italic> ictalurids (60.3 [29.7–122.4] cm) and of the lineage leading to <italic>Pylodictis</italic> and <italic>Noturus</italic> (68.1 [35.4–130.7] cm). Although modern <italic>Ameiurus</italic> exhibit a range of MSLs, the condition within the lineage was reconstructed as stable during the last 35 Ma, with the larger MSL of <italic>A. catus</italic> reconstructed as autapomorphic in this early Miocene lineage. Similarly, the large maximum size of <italic>Pylodictis olivaris</italic> was reconstructed as autapomorphic to this early Eocene lineage rather than as an ancestral condition shared among other modern species with large MSLs (<italic>Ictalurus furcatus</italic>: 165 cm; <italic>I. punctatus</italic>: 127 cm). Within the <italic>Noturus</italic> lineage, MSL was reconstructed as reducing rapidly to a value more typical of the modern species early in their history and which changed rather little after that, echoing the results of the MCMC analyses in BayesTraits.</p>
<p>Least-squares regression through the origin identified lnMSL as a nearly significant predictor of species richness (<italic>B</italic> = −0.470, SE = 0.251, <italic>t</italic> = −1.869, <italic>r</italic><sup>2</sup> = 0.132, <italic>P</italic> = 0.07). Fifteen of 24 contrasts were negative, 8 were positive, and 1 was neutral (sign test: not significant, <italic>P</italic> = 0.21). The regression of contrast against node age (height) was positive, indicating a decrease in lnMSL through the history of Ictaluridae, corroborating the results of BayesTraits and the WSP reconstruction. Additional tests suggested independence of the value of lnMSL and species richness but significant variation in the relationship between lnMSL and species richness through time.</p>
</sec>
<sec><title>Correspondence of Diversification Rate and Paleoclimatic Change</title>
<p><xref ref-type="fig" rid="fig3">Figure 3</xref> plots the rate and direction of MOT change for the Cenozoic paleoclimate reconstruction of <xref ref-type="bibr" rid="b114">Zachos et al. (2001)</xref> and the lnλ inferred from point estimates of node ages obtained from the BEAST MCMC analysis. Although variation in the direction and rate of change was noted for both reconstructions, the approaches employed to explore their correlation failed to reject the null hypothesis of no association between the variables, either analyzed with respect to the basic observation of paired changes (χ<sup>2</sup> = 2.96, <italic>df</italic> = 2, <italic>P</italic> = 0.227) or with respect to the rate of MOT change (Kendall's τ<sub><italic>b</italic></sub> = 0.065, <italic>P</italic> = 0.529).</p>
<fig id="fig3">
<label>Figure 3</label><caption><p>Time-series plots comparing the rate and direction of climate change and log per lineage accumulation rate over 58 one-million-year intervals. Both chi-square and Kendall's τ<sub><italic>b</italic></sub>failed to reject the null hypothesis of no association between these two variables, but see text for a discussion of the possible type II error. The abscissa on the upper plot represents no change in mean ocean temperature over 1 million years. The smoothed line above zero represents climate warming, below represents climate cooling and its distance from zero describes the rate of change in °C/Ma. Filled symbols correspond to the diversification rate shifts noted in <xref ref-type="fig" rid="fig1">Fig. 1</xref> and text.</p></caption>
<graphic xlink:href="57-1-116-f3.gif"></graphic>
</fig>
</sec>
</sec>
<sec><title>Discussion</title>
<sec><title>Phylogeny</title>
<p>In evolutionary studies, phylogeny is of profound importance. In the majority of cases the branching pattern is unknown but taxonomic congruence among phylogenies obtained from diverse data sources is considered compelling evidence for their accuracy. In this study, results of the phylogenetic analysis were understandably similar to earlier studies focused on subsets of the data set analyzed here (<xref ref-type="bibr" rid="b37">Hardman and Page, 2003</xref>; <xref ref-type="bibr" rid="b35">Hardman, 2004</xref>; <xref ref-type="bibr" rid="b65">Near and Hardman, 2006</xref>; <xref ref-type="bibr" rid="b21">Egge and Simons, 2006</xref>). Comparison with results obtained from morphological data sets is restricted due to minimal overlap of taxon sample, but with respect to intergeneric relationships, significant differences have been observed (<xref ref-type="bibr" rid="b37">Hardman and Page, 2003</xref>; <xref ref-type="bibr" rid="b35">Hardman, 2004</xref>). Previous phylogenetic studies including exemplars of all ictalurid genera were based on morphological characters polarized according to their commonality in other fish groups; i.e., an implicit outgroup comparison (<xref ref-type="bibr" rid="b49">Lundberg, 1975</xref>, <xref ref-type="bibr" rid="b50">1982</xref>, <xref ref-type="bibr" rid="b51">1992</xref>). Although J. G. Lundbergs' dendrograms place <italic>Ictalurus</italic> sister to (<italic>Ameiurus</italic> (<italic>Pylodictis</italic>, <italic>Noturus</italic>)), the apparent conflict may be due to placement of the root rather than significantly incongruent signal. Other morphologists have sampled catfishes broadly but did not include exemplars of all epigean ictalurids (e.g., <xref ref-type="bibr" rid="b60">Mo, 1991</xref>; <xref ref-type="bibr" rid="b16">De Pinna, 1998</xref>; <xref ref-type="bibr" rid="b17">Diogo, 2004</xref>) and are thus uninformative with respect to intergeneric relationships. A recent survey of nuclear gene sequences among catfishes included samples of the epigean ictalurids but failed to resolve relationships among them convincingly (<xref ref-type="bibr" rid="b98">Sullivan et al., 2006</xref>). Hence, we have no basis to consider the intergeneric resolution recovered here as inaccurate, though it is without convincing MLBP support.</p>
<p>Within the convincingly monophyletic genera, relationships among species of <italic>Ameiurus</italic> were identical to those reported by <xref ref-type="bibr" rid="b37">Hardman and Page (2003)</xref>. Relationships among <italic>Noturus</italic> species were similar to those of earlier studies based on the same or a subset of the data analyzed here (<xref ref-type="bibr" rid="b35">Hardman, 2004</xref>; <xref ref-type="bibr" rid="b9">Burr et al., 2005</xref>; <xref ref-type="bibr" rid="b65">Near and Hardman, 2006</xref>; <xref ref-type="bibr" rid="b21">Egge and Simons, 2006</xref>). Though convincing support of the basal nodes in <italic>Noturus</italic> remains elusive, the pattern emerging from studies of their phylogeny is that the subgenus <italic>Rabida</italic> is monophyletic, whereas <italic>Schilbeodes</italic> is not. Within <italic>Rabida</italic>, the geographic distribution of several species groups corresponds to what might be expected under a peripheral isolates model of speciation (<xref ref-type="bibr" rid="b32">Grady and LeGrande, 1992</xref>). Species groups of <italic>Schilbeodes</italic> also correspond rather well to geography: two species from the Coastal Plain, four species from Atlantic Slope, and finally a clade with a broad distribution throughout eastern North America. The basal lineage of <italic>Noturus</italic> was recovered as the slender madtom (<italic>N. exilis</italic>). This species has a rather large (536,600 km<sup>2</sup>; <xref ref-type="bibr" rid="b32">Grady and LeGrande, 1992</xref>) but fragmented distribution in streams of the Midwestern and southern United States. <italic>Noturus exilis</italic> has been characterized as having considerable genetic structure, with differences suggesting diversification of the extant members of the lineage to have taken place prior to or early in the Pleistocene (<xref ref-type="bibr" rid="b38">Hardy et al., 2002</xref>). Our estimate of the split between the lineage represented today by <italic>N. exilis</italic> and all other <italic>Noturus</italic> is early Oligocene (mean 35.8; 95% HPD 26.8 to 41.9 Ma) during a period of significant (or nearly significant) diversification rate increase (<xref ref-type="fig" rid="fig1">Fig. 1</xref> to <xref ref-type="fig" rid="fig3">Fig. 3</xref>) and dramatic climate cooling (<xref ref-type="fig" rid="fig3">Fig. 3</xref>).</p>
</sec>
<sec><title>Comparison of the Molecular Chronogram and the Fossil Record</title>
<p>Although the comparative richness of the ictalurid fossil record (<xref ref-type="bibr" rid="b49">Lundberg, 1975</xref>, <xref ref-type="bibr" rid="b51">1992</xref>) cannot be fully employed as constraints in divergence time estimation, the temporal distribution of the unused fossils offers a check of the chronology shown in <xref ref-type="fig" rid="fig1">Fig. 1</xref>.</p>
<p>Unfortunately, fossil <italic>Ameiurus</italic> species are difficult to interpret in the present context because <xref ref-type="bibr" rid="b37">Hardman and Page (2003)</xref> demonstrated significant phylogenetic conflict between the morphological data of Lundberg (<xref ref-type="bibr" rid="b49">1975</xref>, <xref ref-type="bibr" rid="b50">1982</xref>, <xref ref-type="bibr" rid="b51">1992</xref>) and the same sequences upon which our phylogeny and chronology are based. Thus, we were reluctant to use fossil species to provide indirect age minima for their sister taxa according to morphology. However, although no fossils of any extant <italic>Ameiurus</italic> species occur outside of the estimates provided in <xref ref-type="fig" rid="fig1">Fig. 1</xref>, divergence times suggest that the minima provided by the majority of <italic>Ameiurus</italic> fossils and those used to justify lower bounds of lognormal priors considerably underestimate lineage birth times.</p>
<p>The fossil record of <italic>Ictalurus</italic> (<xref ref-type="bibr" rid="b49">Lundberg, 1975</xref>, <xref ref-type="bibr" rid="b51">1992</xref>) is consistent with the DNA chronology in <xref ref-type="fig" rid="fig1">Figure 1</xref>. Fossils identified as <italic>I. punctatus</italic> have been found in middle Miocene deposits of South Dakota and Nebraska (<xref ref-type="bibr" rid="b49">Lundberg, 1975</xref>, <xref ref-type="bibr" rid="b51">1992</xref>) and were used to set a lower bound to a lognormal prior specified in the UCLN MCMC analysis. These fossils predate the upper 95th percentile of the HPD for the divergence time of <italic>I. punctatus</italic> and <italic>I. lupus</italic> by at least 15 Ma. A possible explanation for this observation is that <italic>I. lupus</italic> represents a recently evolved species that has diverged from an ancestral form that was morphologically indistinguishable from modern <italic>I. punctatus</italic>. Thus, the Miocene fossils of <italic>I. punctatus</italic> correctly predate the origin of <italic>I. lupus</italic> and characterize the evolution of <italic>I. punctatus</italic> as one with a stable morphology similar to that observed for <italic>P. olivaris</italic> (<xref ref-type="bibr" rid="b49">Lundberg, 1975</xref>, <xref ref-type="bibr" rid="b51">1992</xref>).</p>
<p>We would like to stress that several species of <italic>Ictalurus</italic> were not available for inclusion in this study. Though the diversification rate experiment including these lineages did not identify the node subtending all <italic>Ictalurus</italic> species as the location of a significant shift in diversification rate, their future analysis might offer some insight into the processes of diversification in this larger-bodied clade in Mexico and the southwestern United States.</p>
</sec>
<sec><title>Correspondence of Diversification Rate and Paleoclimatic Change</title>
<p><xref ref-type="bibr" rid="b64">Near et al. (2005)</xref> used a set of consistent fossil calibration points and mitochondrial and nuclear gene sequences to reconstruct the evolutionary chronology of sunfishes and basses (Centrarchidae) in Cenozoic North America. According to a penalized likelihood analysis, <xref ref-type="bibr" rid="b64">Near et al. (2005)</xref> estimated the root node age of centrarchids to be 33.59 ± 3.58–5.77 and suggested that the dramatic cooling of the climate at this time may have played a role in their early diversification as well as the North American ichthyofauna more generally. In line with the hypothesis of a general response of the North American biota, <xref ref-type="bibr" rid="b108">Webb and Opdyke (1995)</xref> characterized the evolution of land mammals as irregularly distributed in time and tied to Cenozoic climate change.</p>
<p>Although the coincidence of the terminal Eocene event and the significant (or nearly significant) increase in diversification rate of <italic>Noturus</italic> is striking (<xref ref-type="fig" rid="fig1">Fig. 1</xref> inset; <xref ref-type="fig" rid="fig3">Fig. 3</xref>), our attempt to quantitatively examine a general association between diversification rate and climate change did not detect a significant relationship. According to the reconstruction of <xref ref-type="bibr" rid="b114">Zachos et al. (2001)</xref>, the Cenozoic climate was almost constantly changing, although the rate and direction of change varied (<xref ref-type="fig" rid="fig3">Fig. 3</xref>). The significant shifts were tightly bounded in time, specific to early branches of the <italic>Noturus</italic> lineage, and apparently coincided with the greatest period of climatic shift in the Cenozoic. However, if a causal relationship exists between climate change and diversification in ictalurids, why is it that only the <italic>Noturus</italic> lineage showed a significant response? The <italic>Ameiurus</italic>, <italic>Ictalurus,</italic> and <italic>Pylodictis</italic> lineages were present at the time but (unless the fossil record for these lineages is misleading) did not respond significantly to the environmental change. Furthermore, the dramatic cooling of the terminal Eocene event was almost matched by an equally dramatic warming of the climate in the Middle-Late Oligocene (<xref ref-type="fig" rid="fig1">Fig. 1</xref> inset; <xref ref-type="fig" rid="fig3">Fig. 3</xref>) but no significant response in diversification rate was noted.</p>
<p>We did not estimate the type II error rate (false negative) in the correspondence analysis of climate change and diversification rate. Failure to reject the null may be due to our use of point estimates of node ages that are, in fact, inaccurate or that our arbitrary choice of one-million-year measurement intervals is a poor reflection of the time scale over which the effect operates. Additionally, diversification events may be the product of a set of cumulative events that collectively create the circumstances under which the event can take place, and division of that set into million-year slices effectively disrupts its detection. And although climate change appears to have been the norm during the Cenozoic, warming climates pose different changes to the environment than does climate cooling so each climatic event likely posed a different set of selective pressures (with different outcomes) that our rather coarse analysis failed to discriminate. Perhaps it was naïve of us to look for a general relationship between an extrinsic factor and diversification rate <italic>within</italic> a lineage history, though we might expect it on the basis of phylogenetic constraint. Or perhaps the response was only effective on ancestors with a particular body size and, therefore, different biology to the other lineages. All these things (and many more) are possible, but accommodating the errors will decrease precision and power to reject or reveal explicit evolutionary phenomena.</p>
<p>We are left with an understanding that evolutionary events operate on the standing diversity at a point in time that is the sum of all prior events and their influence on shaping its species, their communities and distributions. In effect, no two evolutionary events <italic>within</italic> a lineage are comparable and although significant diversification rate shifts may be detected, their causes may be due to entirely different or ephemeral processes that operate only under certain circumstances on a particular distribution of extant diversity. Perhaps we might find general relationships <italic>across</italic> rather than <italic>within</italic> lineages, and running multiple contemporary and sympatric clades through the analytical procedure described here and by others (<xref ref-type="bibr" rid="b63">Moore and Donoghue, 2007</xref>) might help to reveal a general model of macroevolutionary change in the Cenozoic, if there is one to be found.</p>
<p>Interestingly, although <xref ref-type="bibr" rid="b64">Near et al. (2005)</xref> emphasized the influence of the Eocene-Oligocene climatic shift on North American freshwater fish diversification, most of the extant centrarchid genera and species were reconstructed as late Oligocene, Miocene, and Pliocene in age. So, perhaps the importance of the terminal Eocene event as a driver of diversification has been overemphasized and we should consider it more as an important period of extinction rather than an important period of diversification; i.e., newly vacated niches being reoccupied rather than increasing diversity within an already diverse system. Furthermore, based on the distribution of diversification events presented here and by <xref ref-type="bibr" rid="b64">Near et al. (2005)</xref>, we might find more evidence of an association between climate change and diversification rate in the Oligocene and Miocene.</p>
</sec>
<sec><title>Reconstruction of Ancestral MSLs and Correspondence to Diversification</title>
<p>The MSLs of the early nodes in ictalurid history were reconstructed as being ca. 50 to 60 cm, similar to those of the larger modern <italic>Ameiurus</italic>. The much larger MSLs of the extant <italic>Ictalurus furcatus</italic> (165.0 cm), <italic>Pylodictis olivaris</italic> (155.0 cm), and <italic>I. punctatus</italic> (127.0 cm) were reconstructed as autapomorphic increases from smaller ancestors, suggesting a homoplastic evolution of increasing body size within the family. The Paleocene-Eocene <italic>Astephus</italic> were similar in MSL (estimated 44.0 cm; <xref ref-type="bibr" rid="b33">Grande and Lundberg, 1988</xref>) to that estimated at the root node, suggesting that the addition of proximal fossil lineages would have little impact on its estimation and, therefore, support its accuracy (<xref ref-type="bibr" rid="b69">Oakley and Cunningham, 2000</xref>; <xref ref-type="bibr" rid="b25">Finarelli and Flynn, 2006</xref>). Additionally, the MSLs of extant <italic>Cranoglanis</italic> (43.0 cm; Zheng, 1990) further reinforce the ancestral MSL of Ictaluridae as an approximately half-meter fish. The positive correlation of body size and dispersal is a well known phenomenon (<xref ref-type="bibr" rid="b107">Ware, 1978</xref>; <xref ref-type="bibr" rid="b5">Bernatchez and Dodson, 1987</xref>) and a half-meter ancestral ictalurid could presumably navigate the physical and physiological barriers met in a dispersal route through a Beringian land bridge during the Late Cretaceous or Early Tertiary (<xref ref-type="bibr" rid="b36">Hardman, 2005</xref>).</p>
<p>With respect to the species richness discrepancy observed between <italic>Pylodictis</italic> and <italic>Noturus</italic>, the increased MSL of <italic>P. olivaris</italic> (155.0 cm) from an ancestral condition of 68.1 (35.4–122.4) cm could explain the failure of this lineage to diversify. The combination of a preference for habitats that typically connect adjacent drainages in times of abundant rainfall coupled with its breathtaking dispersal within and among seeded systems (<xref ref-type="bibr" rid="b34">Guier et al., 1981</xref>; <xref ref-type="bibr" rid="b46">Kwak et al., 2004</xref>; <xref ref-type="bibr" rid="b8">Brown et al., 2005</xref>) likely maintains and promotes gene flow among populations of <italic>P</italic>. <italic>olivaris</italic> and offers an explanation of the species' morphological homogeneity over time (<xref ref-type="bibr" rid="b49">Lundberg, 1975</xref>, <xref ref-type="bibr" rid="b51">1992</xref>).</p>
<p>A larger MSL for the ancestral <italic>Noturus</italic> than shown by the majority of extant species also makes sense given the large distribution of a genus that today is composed of rather small and fragmented ranges of many small-bodied species. Of the <italic>Noturus</italic> species with large distributions, <italic>N. gyrinus</italic> is atypical for the genus in that it is commonly found in lowland habitats through which its dispersal is presumably enhanced (<xref ref-type="bibr" rid="b100">Taylor, 1969</xref>; <xref ref-type="bibr" rid="b70">Page and Burr, 1991</xref>). <italic>Noturus flavus</italic> is the largest member of the genus at 31.0 cm, so its range can be explained in terms of a larger MSL. <italic>Noturus eleutherus, N. miurus,</italic> and <italic>N. stigmosus</italic> are all less than 15.0 cm but are found in large streams through which they presumably enjoy dispersal throughout the Ohio and Mississippi drainages. The low genetic differentiation (<xref ref-type="bibr" rid="b35">Hardman, 2004</xref>) and large range of the Atlantic Slope <italic>N. insignis</italic> (MSL of 15.0 cm) is anomalous and a subject for further study.</p>
</sec>
</sec>
<sec><title>Conclusions</title>
<p>If we ignore our concerns and let the results tell their story, the analyses of Ictaluridae found diversification rate to have varied significantly during the Cenozoic and significant (or nearly significant) increases were implied for early nodes in the <italic>Noturus</italic> lineage. The evolution of lnMSL followed a directional (decreasing) model and was found to be a nearly significant predictor of species richness, with clades composed of small species being proportionally more species rich than expected under a null model. The chronology of diversification describes the origins of the extant genera during the Paleocene and early Eocene and the majority of extant species to be Oligocene and Miocene in age. Climate change did not significantly affect diversification rate throughout the history of the lineage.</p>
<p>We estimated the maximum standard length of the ictalurid ancestor to be approximately 50 cm, comparable to Eocene ictalurids (<italic>Astephus</italic>) and similar to modern sizes of <italic>Ameiurus</italic> and the Asian sister taxon <italic>Cranoglanis</italic>. Based on the properties of modern fishes of similar size, the hypothetical ancestor would be suitably sized to disperse from Asia into North America through freshwater systems of Beringia (<xref ref-type="bibr" rid="b36">Hardman, 2005</xref>).</p>
<p>The covariation of increasing size, large distribution, and low diversity appears to be a general one shown by <italic>Pylodictis olivaris, Ictalurus furcatus,</italic> and <italic>I. punctatus</italic>. All three species regularly grow well over a meter and have large natural distributions. Additionally, all three appear to be rather ancient species with conservative morphologies that have independently increased their maximum standard lengths from smaller ancestors, as implied by the fossil record and reconstructions presented here. Presumably, the common diversification process of peripheral isolation fails to operate when species evolve large body sizes and, consequently, expand their distributions within which dispersal and migration maintain or increase gene flow. The small-bodied lineage, on the other hand, has experienced a diversification rate significantly higher than its larger cousins and the patchy distributions of many modern <italic>Noturus</italic> suggest a separate set of evolutionary processes have applied to this clade.
<graphic xlink:href="57-1-116-uf1.gif"></graphic></p>
</sec>
</body>
<back>
<ack>
<title>Acknowledgment</title>
<p>Special thanks to B. Moore and J. Lundberg for their detailed, thoughtful, and tremendously helpful comments on an earlier version of this paper. Also, J. Knouft, L. Page, and A. Summers provided excellent counsel on macroevolutionary matters, North American freshwater fishes, and their thoughts on the importance of body size. N. Isaac, A. Meade, B. Moore, and A. Rambaut provided software and technical support. We thank H. Henttonen for providing logistic and informatics support during the course of this project. M.H. was supported by the All Catfish Species Inventory (NSF: DEB 0315963) and L.H. by a Finnish Academy Postdoctoral Research Grant (no. 108372; Wickström et al., 2005).</p>
</ack>
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</article></istex:document></istex:metadataXml><mods version="3.6"><titleInfo><title>The Relative Importance of Body Size and Paleoclimatic Change as Explanatory Variables Influencing Lineage Diversification Rate: An Evolutionary Analysis of Bullhead Catfishes (Siluriformes: Ictaluridae)</title></titleInfo><titleInfo type="alternative" contentType="CDATA"><title>The Relative Importance of Body Size and Paleoclimatic Change as Explanatory Variables Influencing Lineage Diversification Rate: An Evolutionary Analysis of Bullhead Catfishes (Siluriformes: Ictaluridae)</title></titleInfo><name type="personal"><namePart type="given">Michael</namePart><namePart type="family">Hardman</namePart><affiliation>Laboratory of Molecular Systematics, Finnish Forest Research Institute, Jokiniemenkuja 1, 01301, Vantaa, Finland</affiliation><affiliation>E-mail: m.hardman@mac.com</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">Lotta M.</namePart><namePart type="family">Hardman</namePart><affiliation>Laboratory of Molecular Systematics, Finnish Forest Research Institute, Jokiniemenkuja 1, 01301, Vantaa, Finland</affiliation><affiliation>E-mail: m.hardman@mac.com</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">Allan</namePart><namePart type="family">Baker</namePart><affiliation>Laboratory of Molecular Systematics, Finnish Forest Research Institute, Jokiniemenkuja 1, 01301, Vantaa, Finland</affiliation><affiliation>E-mail: m.hardman@mac.com</affiliation><role><roleTerm type="text">editor</roleTerm></role></name><typeOfResource>text</typeOfResource><genre type="research-article" displayLabel="research-article" authority="ISTEX" authorityURI="https://content-type.data.istex.fr" valueURI="https://content-type.data.istex.fr/ark:/67375/XTP-1JC4F85T-7">research-article</genre><originInfo><publisher>Taylor & Francis</publisher><dateIssued encoding="w3cdtf">2008-02</dateIssued><copyrightDate encoding="w3cdtf">2008</copyrightDate></originInfo><abstract>We applied Bayesian phylogenetics, divergence time estimation, diversification pattern analysis, and parsimony-based methods of ancestral state reconstruction to a combination of nucleotide sequences, maximum body sizes, fossils, and paleoclimate data to explore the influence of an extrinsic (climate change) and an intrinsic (maximum body size) factor on diversification rates in a North American clade of catfishes (Ictaluridae). We found diversification rate to have been significantly variable over time, with significant (or nearly significant) rate increases in the early history of Noturus. Though the latter coincided closely with a period of dramatic climate change at the Eocene-Oligocene boundary, we did not detect evidence for a general association between climate change and diversification rate during the entire history of Ictaluridae. Within Ictaluridae, small body size was found to be a near significant predictor of species richness. Morphological stasis of several species appears to be a consequence of a homoplastic increase in body size. We estimated the maximum standard length of the ictalurid ancestor to be approximately 50 cm, comparable to Eocene ictalurids (Astephus) and similar to modern sizes of Ameiurus and their Asian sister-taxon Cranoglanis. During the late Paleocene and early Eocene, the ictalurid ancestor diversified into the lineages represented by the modern epigean genera. The majority of modern species originated in the Oligocene and Miocene, most likely according to a peripheral isolates model of speciation. We discuss the difficulties of detecting macroevolutionary patterns within a lineage history and encourage the scrutiny of the terminal Eocene climatic event as a direct promoter of diversification.</abstract><subject><genre>kwd</genre><topic>Clade assymmetry</topic><topic>Eocene extinction</topic><topic>historical biogeography</topic><topic>North American ichthyofauna</topic><topic>relaxed clock</topic><topic>speciation</topic><topic>Cenozoic freshwater fishes</topic></subject><relatedItem type="host"><titleInfo><title>Systematic Biology</title></titleInfo><genre type="journal" authority="ISTEX" authorityURI="https://publication-type.data.istex.fr" valueURI="https://publication-type.data.istex.fr/ark:/67375/JMC-0GLKJH51-B">journal</genre><subject><topic>Regular Articles</topic></subject><identifier type="ISSN">1063-5157</identifier><identifier type="eISSN">1076-836X</identifier><identifier type="PublisherID">sysbio</identifier><identifier type="PublisherID-hwp">sysbio</identifier><part><date>2008</date><detail type="volume"><caption>vol.</caption><number>57</number></detail><detail type="issue"><caption>no.</caption><number>1</number></detail><extent unit="pages"><start>116</start><end>130</end></extent></part></relatedItem><identifier type="istex">7BB9A3067B7287CA2E8CEB47C586DFE0C34B3A42</identifier><identifier type="DOI">10.1080/10635150801902193</identifier><accessCondition type="use and reproduction" contentType="copyright">© 2008 Society of Systematic Biologists</accessCondition><recordInfo><recordContentSource authority="ISTEX" authorityURI="https://loaded-corpus.data.istex.fr" valueURI="https://loaded-corpus.data.istex.fr/ark:/67375/XBH-GTWS0RDP-M">oup</recordContentSource><recordOrigin>© 2008 Society of Systematic Biologists</recordOrigin></recordInfo></mods><json:item><extension>json</extension><original>false</original><mimetype>application/json</mimetype><uri>https://api.istex.fr/document/7BB9A3067B7287CA2E8CEB47C586DFE0C34B3A42/metadata/json</uri></json:item></metadata><annexes><json:item><extension>gif</extension><original>true</original><mimetype>image/gif</mimetype><uri>https://api.istex.fr/document/7BB9A3067B7287CA2E8CEB47C586DFE0C34B3A42/annexes/gif</uri></json:item></annexes><serie></serie></istex></record>Pour manipuler ce document sous Unix (Dilib)
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