Year: 2012 Page 16 of 47

Figure from Leal and Powell paper showing that members of the same ecomorph category are not convergent in brain structure.

The Caribbean anole radiation is famous for its convergence. First detected in features related to habitat use and locomotion, such as limb length and toepad size, we now know that the Greater Antillean ecomorphs are convergent in many other attributes such as sexual dimorphism, territory structure and head shape. One might wonder what other features are convergent as well. For example, brains. The anole ecomorphs differ in the complexity of the environments in which they live, which might lead to selection for different brain configurations in different habitats. Brian Powell set out to examine anole brains for his just completed doctoral dissertation at Duke University, and he has now published the results. The short story: the anole ecomorphs are not convergent in brain structure! You can read more details in Chipojolab’s first-hand account of this paper, or check out the paper’s abstract here:

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Dan Rabosky and co-authors have just published an important report on patterns of organismal diversity in PLOS Biology, with one of their main conclusions being that clade age does little to explain species richness.  Luke Harmon has a commentary on this article in the same issue of PLOS Biology, and I’ll refer readers there for a general summary of the work’s implications.  I wanted to give this article a shout-out here at Anole Annals because they used an anole as their icon for squamates in Fig. 3 (see above).

Inspection of their supplemental Table 2 and consultation with the authors, however, reveals that anoles were inadvertently left out of the final analyses due to a book-keeping error involving use of the timetree age for Iguanidae sensu Schulte et al. 2003 but the species richness for Iguanidae sensu Frost & Etheridge 1989. (A quick taxonomic review for the uninitiated: The family diagnosed as Iguanidae by Frost and Etheridge included only a subset of the species previously regarded as members of the much larger family Iguanidae.  Frost and Etheridge assigned Anolis and many of the other genera previously included in Iguanidae to other newly defined families.  They considered this taxonomic revision necessary because they did not recover a monophyletic Iguanidae sensu lato.  Because molecular phylogenetic analyses do tend to recover a monophyletic Iguanidae sensu lato, some subsequent authors, including Schulte et al. 2003, have advocated retention of Iguanidae sensu lato and treatment of Frost & Etheridge’s families as subfamilies [see Daza et al. 2012 for another perspective on this taxonomic debate].)

If we imagine crudely adding a circle to represent Anolis in Rabosky et al.’s figure 3 (assuming an age of ~50 mybp and species richness of ~400 for the genus), its clear that anoles would be among the youngest, yet also most species rich, of all squamate clades, providing further support for Rabosky et al.’s main conclusion that clade age has little role in explaining clade richness.

When alerted of this issue, Rabosky and his co-authors re-ran their analyses including anoles and their relatives (i.e., Polychridae/Polychrotidae of Frost and Etheridge) as well as all of the other Frost and Etheridge families that were overlooked for the same reason (e.g., Tropiduridae, Phyrnosomatidae).  Rabosky sent me a figure that illustrates the position of all these missing clades (in blue), including the clade that includes Anolis (in red) as well as the other squamate clades in the original analysis (in grey).  Because many of these clades stem from series of basal branching events within Iguanidae sensu lato and are relatively similar in age, they rather nicely illustrate the reported absence of a correlation between clade age and species richness.  Not surprisingly, Rabosky et al.’s overall conclusions about clade age and species richness are unchanged by inclusion of these additional datapoints.

At the end of the day, this discussion nicely illustrates how monkeying around with the names of formal Linnean ranks can cause chaos for anyone who is not intimately familiar with a particular name’s complete history.

Rabosky, D. L., G. J. Slater, and M. E. Alfaro (2012). Clade Age and Species Richness Are Decoupled Across the Eukaryotic Tree of Life PLOS Biology DOI: 10.1371/journal.pbio.1001381

Wrapping up our coverage of the World Congress of Herpetology held in Vancouver last week, I have a report on Nick Crawford’s talk on the genetics of colorful pigmentation in Anolis.  Nick began by talking about the basic types of pigments that contribute to anole coloration, which include both pteridines and carotenoids.  Synthesis of pteridines is much better understood, thanks largely to work on zebra fish (reviewed in Braasch et al. 2007).  Nick first showed preliminary evidence from rtPCR analyses suggesting that specific genes along the pteridine synthesis pathway differ in predictable ways among parts of anoles with different coloration (e.g., white venter, green dorsum, pink dewlap).

Crawford went on to note that pteridines may be less important to dewlap coloration than are carotenoids, but that the latter represent a bit of a black box genetically and developmentally.  Crawford then discussed a project in which he uses a bulk segregant approach to ask if regions of the genome associated with color differentiation can be identified by examining genomic sequence data from species with polymorphic coloration.  Crawford was particularly interested in the polymorphic Lesser Antillean Anolis marmoratus.  He obtained sequence data from two phenotypically distinct populations of this species using the Illumina hiSeq platform.  Fortunately this data could be aligned to the A. carolinensis genome, and showed a relatively high degree of synteny with this previously published genome.  Analyses of the new A. marmoratus dataset are still in their early stages, but preliminary analyses recover 1,300 fixed SNPs (only 330 of which appear to be exonic) and suggest the presence of genomic islands of differentiation similar to those reported in many other recently diverged species and incipient species.

Note Added in Press:

One talk we failed to cover at WCH was by Chris Schneider on a similar topic. Here’s the Abstract:

Schneider, Christopher (Boston University); Crawford, Nicholas; McGreevy, TJ; Messana, Nick (Boston University, Canada)

The genetic basis of phenotypic variation and divergence in Anolis marmoratus

In what should be our final belated post about talks at the Evolution meetings in Ottawa last month, I’d like to share some results from Bryan Falk from Susan Perkins’s Lab American Museum of Natural History.  Bryan has been investigating the diversity of anole malaria parasites (Plasmodium).  Like many other species of vertebrates, anoles have their own strains of malaria (not the same as the ones that effect us humans), and these lizard malaria have been the focus of numerous fascinating research projects over the years (see Schall 1996 for a review).

Bryan’s work investigated phylogenetic relationships among West Indian strains of lizard malaria using sequence data from mitochondrial DNA plus six nuclear loci.  He found that Plasmodium samples on most islands form monophyletic groups, although some clades are found in both Florida and Cuba, suggesting travel between these two regions.  Bryan also reported very low overall genetic diversity, the presence of most genetic variation among (rather than within) populations, and no evidence for purifying selection.  Bryan’s previous work used tree-based delimitation to diagnose previously unrecognized or ambiguous taxa of Plasmodium on Hispaniola, and his new work uses a similar approach across a broader geographic scale.  In the new study, species tree analyses tend to recover island-specific clades and identify 11 potentially unrecognized species within Plasmodium floridense (see Perkins 2000 for more on species delimitation in Plasmodium). Bryan’s time calibration work suggests that intra-island divergences are very young and his demographic analyses suggests that recent divergence and serial bottlenecks may be responsible for low diversity with in populations but high divergence among populations.  It seems like more exciting new results with anole malaria on are on the horizon from Bryan and his collaborators.

The New York Times covered the story, too. http://graphics8.nytimes.com/images/2012/08/08/blogs/cat/cat-blog480.jpg

We reported earlier this month on the talk at the Ecological Society of America where a University of Georgia researcher put kitty cams on housecats to see where they went and what they did. And one finding: they caught a lot of anoles! USA Today ran an article on the front page, and included a video online that has some grisly (ok, not that grisly) footage of this, as well as other cool stuff (encounters with other animals, secret lives of housecats). Check it out!