Author: Jonathan Losos Page 22 of 130

The latest work on genetic differentiation and species status within the Anolis distichus group has just been published by MacGuigan, Geneva and Glor in Ecology and Evolution. In line with previous work from the Glor lab, the study finds evidence for seven distinct evolutionary lineages worthy of recognition as species, and further finds that variation in dewlap color in some cases does not correlate with geographic isolation. Finally, geographic isolation seems to play a key role in genetic divergence.

Here’s the abstract, followed by a few comments:

Abstract

Delimiting young species is one of the great challenges of systematic biology, particularly when the species in question exhibit little morphological divergence. Anolis distichus, a trunk anole with more than a dozen subspecies that are defined primarily by dewlap color, may actually represent several independent evolutionary lineages. To test this, we utilized amplified fragment length polymorphisms (AFLP) genome scans and genetic clustering analyses in conjunction with a coalescent-based species delimitation method. We examined a geographically widespread set of samples and two heavily sampled hybrid zones. We find that genetic divergence is associated with a major biogeographic barrier, the Hispaniolan paleo-island boundary, but not with dewlap color. Additionally, we find support for hypotheses regarding colonization of two Hispaniolan satellite islands and the Bahamas from mainland Hispaniola. Our results show that A. distichus is composed of seven distinct evolutionary lineages still experiencing a limited degree of gene flow. We suggest that A. distichus merits taxonomic revision, but that dewlap color cannot be relied upon as the primary diagnostic character.

The authors suggest that there are at least seven species within the distichus complex, but they suggest that it is premature to recognize them officially at this time. Nonetheless, Poe et al. in their recent Systematic Biology paper (hey! who’s going to write a post on this one?) recognize at least some of these taxa as distinct species.

Finally, I do have one tiny bone to pick. The authors state:

“Together these results suggest that dewlap color is not by itself a reliable diagnostic trait in the A. distichus complex, and perhaps in anoles more broadly.”

I take umbrage with the final statement, “and perhaps in anoles more broadly.” The distichus complex has always been recognized as the major exception to the idea that dewlap color variation relates to reproductive isolation. Consequently, demonstrating what has been suggested—with some evidence—for 40 years doesn’t necessarily argue against the role of the dewlap in reproductive isolation more generally. Now, you may quibble with the data underlying this general proposition, and it certainly is worthy of further study, but the results of this study confirm what was already recognized as an exception to this general rule..

Bill Rainey observed this lizard on a restored portion of one temple at Altun Ha, an ancient Mayan city in modern-day Belize, in an area shaded by trees. Anyone know what it is?

The following is taken from the Society for the Study of Amphibian and Reptile’s website:

Catalogue of American Amphibians and Reptiles

The Catalogue consists of accounts of taxa prepared by specialists, including synonymy, description, diagnosis, phylogenetic relationships, published descriptions, illustrations, distribution map, and comprehensive list of literature for each taxon. Over 900 accounts have been published since the initiation of the series in 1963. The series covers amphibians and reptiles of the entire Western Hemisphere. Previously, accounts were published as loose-leaf separates; beginning in 2013 accounts are published as on-line PDFs.  All accounts are open access and are available for free download at the University of Texas Library Repository.

Just this week, one of the latest catalogue entries is for the little known Anolis ruibali of Cuba, written by Robert Powell, Javier Torres, and Nils Navarro Pacheco.

Poor Anolis, snack box of the jungle. Seems that just about anything will eat an anole. So, it’s not surprise to learn that the teid lizard Kentropyx calcarata joins the lizard of anole consumers. So report Franzini et al. in a recent report in Herpetology Notes. Anolis fuscoauratus was the unfortunate victim, the crime discovered by examination of stomach contents.

Consider two lizard species that differ in limb length, with one species having relatively longer legs than others. During development, how does this difference arise? Do the limbs start at the same length when they first appear in the embryo, but grow at a greater rate in the longer-legged species? Or is the initial limb bud longer in the embryo of the longer-legged species, and then the rate of growth the same in the two species, preserving the initial difference?

Thom Sanger’s elegant work showed that the latter answer is correct for Anolis: the limb buds of long-legged species start out longer and then grow in parallel with those of shorter-legged species.

But does this finding also hold when comparing across a broader range of lizards? Robin Andrews and Sable Skewes decided to find out, comparing embryos of a chameleon, two geckos, and the brown anole.

The answer: the same pattern as within anoles! And it applies to tail length (but not head length) as well as limbs.

Thanks to the work of Roger Thorpe and colleagues, Lesser Antillean anoles are renowned as an example of adaptive geographic variation. On many islands in the Lesser Antilles, populations in wet areas, where vegetation is lush, are green in color, whereas those in more xeric areas tend to be a drab gray, often with markings on their back. This pattern is repeated on many different islands, the convergent geographic variation thus making a strong case for the adaptive basis of anole coloration.

See Pavitra Muralidhar’s previous post for more information on geographic variation in Lesser Antillean anoles.

In a new paper in PLoS One, Thorpe takes this work a step further, asking whether we can use the parallel patterns seen across Lesser Antillean islands to predict the coloration of an anole species on another island. The focal species is Anolis bonairensis, which occupies the extraordinarily dry island of Bonaire (see our previous posts on this species).

The prediction: A. bonairensis should be grayer and drabber than populations of anoles that occur at the driest sites on Lesser Antillean answers.

The answer: yes! Just as predicted, Anolis bonairensis is one drab lizard. Score one for evolutionary predictability!

Anolis bonairensis is represented by the red circles. The x-axis goes from aridity on the left to the most mesic on the right. As you can see, A. bonairensis‘s color and patterning is well-predicted by variation in other species.

Anolis biporcatus, one of the prettiest of anoles. Photo by Thomas Marent

Anolis biporcatus is, if I’m not mistaken, the largest mainland beta/Norops anoles, attaining a length of ca. 100 mm snout-vent. In addition, it has an enormous geographic distribution, ranging from southern Mexico to Ecuador. In a new paper in Salamandra, a team of New Mexican and Ecuadorian biologists headed by Janet Armstead have sliced off part of the species, raising the Ecuadorian/Colombian A. biporcatus parvauritus to species status. They make this decision based on a detailed analysis of morphology and molecular data. Their data also find deep genetic subdivisions within A. biporcatus in Costa Rica, suggesting that there may be more cryptic species awaiting recognition.

A key difference between the species is the color of the distal scales on the dewlap of males, white in biporcatus, black in parvauritus.

Note, too, that like many mainland anoles, the males and females have very different dewlaps.

Here’s the distribution of the two species:

Two male festive anoles (Anolis sagrei) fighting in Texas. From netscape.net‘s Facebook page.

This is reminiscent of similar battles in Sitana, like the photo below. Of course, we know all about Sitana fights here on AA.

Liam Revell has developed a method, which he explains in Phytools.