Anole Annals

Convergent evolution is Anolis Lizards’ middle name, and so it is with great interest that we read two brand-spanking new papers on convergent evolution. The first is by  Arbuckle et al. out of the University of Liverpool. Published in Methods in Ecology and Evolution, the paper describes a new method for quantifying the strength of convergent evolution. You’ll have to read the paper for the details, but the gist of the method is that convergence is greatest either when species are greatly different phenotypically from other species or when the convergent species are distantly related phylogenetically.

And the focal taxon used to demonstrate the method with empirical data? Why, none other than Greater Antillean ecomorphs. The paper found that in “In Anolis lizard data set, perhaps the most notable finding is that ecomorphs differ in the strength of their convergence—grass-bush and trunk-ground anoles stand out as having particularly strong convergence compared to others. Furthermore, some traits are more strongly convergent within some ecomorphs but not others. Therefore, patterns of convergence in particular traits are ecomorph specific.” Specifically, “analyses found the strongest convergence in limb length occurred in grass-bush anoles compared to the other ecomorphs, consistent with Losos’ (1990b, 2009) finding of relationships between limb length and jumping and sprinting (perhaps particularly important for grass-bush anoles). The strong convergence of lamellae number detected in trunkground anoles suggests that there is a notable degree of adaptation in this trait.”

The abstract of the paper is appended at the bottom of this post.

Meanwhile, in a non-anole example, Collar and colleagues, in a paper in the American Naturalist, looked at convergent evolution in snail-eating moray eels. The authors found that the durophagous eels evolved in generally the same direction morphologically relative to their non-snailivorous relatives, but that there was substantial variation among the shell-crackers, actually more variation than seen among their relatives.

The authors explain this “imperfect convergence” in this way:  “we show that following 10 transitions to durophagy (eating hard-shelled prey) in moray eels (Muraenidae), cranial morphology repeatedly evolved toward a novel region of morphological space indicative of enhanced feeding performance on hard prey. Disparity among the resulting 15 durophagous species, however, is greater than disparity among ancestors that fed on large evasive prey, contradicting the pattern expected under convergence. This elevated disparity is a consequence of lineage specific responses to durophagy, in which independent transitions vary in the suites of traits exhibiting the largest changes. Our results reveal a pattern of imperfect convergence, which suggests shared selection may actually promote diversification because lineages often differ in their phenotypic responses to similar selective demands.”

Such imperfect convergence is not unknown among anoles. For example, Langerhans et al. showed that despite the convergence among the ecomorphs, there were also island-specific effects that produced variation among members of an ecomorph. Moreover, a larger scale example is the comparison of mainland and Greater Antillean anoles. Is the lack of convergence due to environmental differences, or is it an example of species evolving different adaptations to living in the same environment?

Exciting times for those of us interested in convergent evolution!

The abstract of the Arbuckle et al. paper:

Read More

And it’s a looker!

The species, described recently in Amphibian & Reptile Conservation by Fernando Ayala-Varela and colleagues, comes from the western slope of the Andes in Ecuador. In appearance, it’s most similar to A. gemmosus, which occurs to the north. Detailed examination shows it to be most phenotypically similar to that species and A. otongae, and DNA analysis indicates that A. gemmosus is its sister taxon.

Check out the paper, which has lots of lovely photos not only of the new species, but of some of the species with which it is sympatric.

Sleeping Sitana

If you’re in the field looking for lizards, knowing where they sleep can be tremendously useful. Anyone who’s tried catching an anole at night knows how much easier this can be than catching it during the day.  When I began working with Sitana, therefore, I was keen to locate where these lizards slept. Being primarily terrestrial, it made sense that they would sleep under rocks, in cracks in the ground, or buried beneath grass, bushes, or leaf litter. I had some indirect evidence for the utilization of these locations as sleeping sites–I had seen lizards emerging from and retreating to these locations early in the morning and late in the evening, respectively.

However, I did not expect that fan-throated lizards would sleep completely in the open on the ground. Yet that is precisely what my colleague Divyaraj Shah recently observed. You can see the lizard’s head pointing downwards, resting on the ground below–he does not seem disturbed at this point.

Is it common for terrestrial lizards to sleep in open, unsheltered spots?

Keratins are the structural proteins of skin, hair, nails, feathers, and scales. There are 54 described  keratins in humans, a subset of which has also been found in the green anole genome. Distinct combinations of keratins in skin appendages are what give these tissues their unique properties such as flexibility, rigidity, or cornification (i.e., the process of forming an epithelial barrier). Lizards have a number of specialized scale types, likely due to the distinct distribution of keratins in those scales. Dating back at least a decade, Lorenzo Alibardi and colleagues have been making great progress describing the keratin gene family in lizards and describing the distribution of these proteins across the body. Alibardi has recently added to this long series with a description of keratin localization in the lamellae of Anolis carolinensis. Because I am not an expert in keratin biology I will let the Abstract give you the details:

ABSTRACT Knowledge of beta-protein (beta-keratin) sequences in Anolis carolinensis facilitates the localization of specific sites in the skin of this lizard. The epidermal distribution of two new beta-proteins (betakeratins), HgGC8 and HgG13, has been analyzed by Western blotting, light and ultrastructural immunocytochemistry. HgGC8 includes 16 kDa members of the glycine-cysteine medium-rich subfamily and is mainly expressed in the beta-layer of adhesive setae but not in the setae. HgGC8 is absent in other epidermal layers of the setae and is weakly expressed in the beta-layer of other scales. HgG13 comprises members of 17-kDa glycine-rich proteins and is absent in the setae, diffusely distributed in the beta layer of digital scales and barely present in the beta-layer of other scales. It appears that the specialized glycine-cysteine medium rich beta-proteins such as HgGC8 in the beta-layer, and of HgGC10 and HgGC3 in both alpha- and beta layers, are key proteins in the formation of the flexible epidermal layers involved in the function of these modified scales in adaptation to contact and adhesion on surfaces.

Fig. 10 from Alibardi 2014

Courtesy Nirvana Reptiles

Gunther Köhler has just published a paper in Zootaxa describing the many characters used in anole species descriptions. Here’s how he explains the endeavor:

“Anolis are important research organisms and many articles are published every year dealing with different aspects of the biology of these lizards. However, at this point we still lack detailed and standardized descriptions of all recognized species of Anolis. The species descriptions found in original descriptions, reviews of species groups, or faunal treatments are extremely heterogeneous in regard to content, usage of terms, semantic issues, and characters included. For example, some authors (e.g., Underwood & Williams 1959; Savage & Villa 1986; Köhler 2008) count the number of subdigital lamellae under Phalanges II–IV whereas others (e.g., Schwartz 1973; Williams 1995; Poe et al. 2012) report only the lamellae under Phalanges II and III. Even when the same characters are reported, often differences in definitions are evident with different authors scoring the same character differently, i.e., having different threshold levels for scoring qualitative characters (e.g., whether to consider a scale to be smooth, faintly, or weakly keeled, or not, slightly or distinctly enlarged relative to adjacent scales). Also, the way the data are generated can differ widely depending on the applied methodology. In 1995, Williams provided definitions for 37 morphological characters intended for usage in a computerized key for anoles. Williams’ (1995) approach aimed mostly to bring definitions and encodings of morphological characters usable in a computer program. Therefore, he was forced to simplify many of the included character states thereby masking the extent of variation actually observed in the genus Anolis. This article aims to provide definitions of external morphological characters that are useful in Anolis taxonomy with the goal of establishing a reference for future taxonomic work with these lizards. I am confident that a description containing the set of characters defined here will be reasonably complete for the majority of species. In species that show special morphological differentiations (such as the rostral appendage in A. proboscis), these special features need to be addressed of course. I have included many images illustrating the variation in the characters discussed, although I do not attempt to provide a comprehensive review of the variation in external morphology in anoles.”

A variety of morphometric characters from snout-vent length and head width to postcloacal scale width. Here’s one as an example:

Diameter of parietal scale. The longitudinal (LDP) and transverse (TDP) diameters of the parietal scale are measured. LDP and TDP both are measured at the greatest length and width, respectively. Slender projections of the parietal scale should be ignored in cases where these are beyond the normal concave or convex outline of the scale.

The heart of the paper is a description of a large number of scalation characters and their various alternative states. For example:

Condition of supraocular scales (CSO). These vary from smooth or rugose to weakly or strongly keeled; keeling can be uni- or multicarinate. Examples are given in Fig. 12.

Condition of circumorbital scales (COS). In many species of anoles, a row of small scales separates the enlarged supraocular scales from the scales of the supraorbital semicircles. Thus, this character refers basically to the scales situated medially to the enlarged supraocular scales; laterally to the enlarged supraocular scales usually numerous small scales are present without differentiated scales that can be identified as circumorbitals. Considerable intra- and interspecific variation can be observed in this character as exemplified in Anolis dunni (Fig. 13) with the circumorbital series varying from complete (one or more rows of scales) to incomplete or absent. Whenever one or more enlarged supraocular scales are in contact with scales of the supraorbital semicircles, the circumorbital series are incomplete or absent.

And one more set of examples:

Number of scales between supraorbital semicircles (IO). In most species of anoles a pair of semicircular series of enlarged scales is present in the frontal region between the supraocular discs. The minimum number of scales between the supraorbital semicircles is determined (i.e., usually at the narrowest point; Fig. 22).

Number of scales between supraorbital semicircles and interparietal plate (IP/IO). The minimum number of scales between the supraorbital semicircles and the interparietal plate is determined (Fig. 22). This character obviously is ignored in species that lack a differentiated interparietal plate (e.g., Fig. 22B).

Size of scales adjacent to interparietal plate (ScIP). The relative size of the scales surrounding the interparietal plate is noted. In some species the size of the scales anterior to the interparietal plate differs from those situated posteriorly to it. See examples in Fig. 22.

This looks to be a very useful contribution, particularly as the number of newly described anoles continues to rise.

Several days ago, I reported on skeletal anomalies from this year’s trip to the Bahamas and wondered what cool stuff we might see next. Much to my surprise, the next surprise turned up the very next day, in the form of Mexican anole maestro Levi Gray, making his first appearance in the Caribbean. Welcome to the big leagues, Levi!

The next night, Levi strolled down to our place to do some night herping–and wouldn’t you know?–en route the very first Anolis smaragdinus he had ever seen turned out to be of the three-footed variety. Add another example to our parade of limb-reduced anoles.

Later on, while out looking for more greens, we came across this pair of lizards snoozing.

But closer examination shows that that’s not a pair, but a trio, with one anole sleeping on top of another. Now, that’s something I’ve never seen before!

Lastly, my favorite shots of the trip, now finished.

Anolis sagrei. Photo by Jonathan Losos

Anolis distichus. Photo Jonathan Losos

Anolis smaragdinus. Photo by Jonathan Losos