New Multilocus Phylogeny Confirms that Polychrus is Not Sister to Anolis

A time calibrated tree from Townsend et al. and photographs of Polychrus (from http://reptile-database.reptarium.cz/species.php?genus=Polychrus&species=gutturosus), Anolis, and Basiliscus (from http://scienceblogs.com/tetrapodzoology/2009/01/something_new_about_basilisks.php)..

For decades, anole have been assigned to Polychrotidae, a family or subfamily of Iguania whose core members have always included Anolis and Polychrus.  In spite of the  morphological similarities shared by these genera, molecular studies conducted over the past decade have consistently recovered a non-monophyletic Polychrotidae and have never recovered strong support for a sister relationship between Polychrus and Anolis.  In recent Bayesian and maximum likelihood analyses of 29 loci sampled from 47 iguanians and 29 outgroup taxa, Townsend et al. (2011) drive the final nail in the coffin of the notion that Anolis and Polychrus are closely related and form a clade that should continue to be recognized as Polychrotidae.  The sister-group relationship between Anolis and Polychrus is completely absent from the posterior distribution of trees generated from Townsend et al.’s 29-locus concatenated dataset and this relationship appears in only one or two of their 29 single-gene trees.  As a result, Townsend et al. limit Polycrhotidae to Polychrus and resurrect the family name Dactyloidae for Anolis.  Although they acknowledge that Dactyloidae is a less intuitive name for this clade than Anolidae, the latter is junior synonym of the former, having been coined by Cope (1864) some 20 years after Fitzinger (1843) recognized Dactyloidae.  Students of squamate phylogenetic systematics should definitely check this paper out, Townsend et al.’s results concerning Polychrotidae are only one of their many interesting insights.

8 thoughts on “New Multilocus Phylogeny Confirms that Polychrus is Not Sister to Anolis

  1. Here’s a bold suggestion: instead of having to resurrect 170 year old names and continually more finely splitting the taxonomy every time a new study is published, why not just use the name that prevailed for decades: Iguanidae? Molecular work has convincingly demonstrated that the Iguanidae (in the broad sense) is monophyletic, and there never was compelling justification to split it up in the first place. The Townsend et al. phylogeny only included 47 species; undoubtedly, as more problematic taxa are added (e.g., other refugees from the old Polychrotidae), we will find additional cases of non-monophyly of the Townsend et al. clades, requiring yet further revision. Furthermore, additional work may strongly unite currently weakly supported clades (is it really useful for Polychrus and Leiocephalus to each form monotypic families?). This continual name-changing is disruptive to users of phylogenies and unnecessary because the old family Iguanidae is monophyletic, and we can use informal or subfamily names for clades, as we used to do. We should try to avoid being in a situation where we change our classification system every time a new phylogeny appears.

  2. Application of new names can definitely lead to confusion when taxon sampling is relatively sparse at the species level and some relationships remain poorly resolved (see previous efforts to divide Anolis). In iguanians, a number of clades have been recognized for decades and have fairly well-established significance in the herp community; whether these are recognized as families, subfamilies, rankless clades, or just informally, I think its useful to have names for these clades and to tweak their composition as necessary. Given that I’m not a big fan of Linnean taxonomy, however, I’m not going to disagree with the notion that its a bit awkward to have to come up with family names for clades that currently consist of a single genus.

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