Year: 2013 Page 2 of 37

Results of mating trials in Ng et al.’s study. Top two rows are within-population crosses; bottom two are between crosses from different populations that differed in dewlap color. Note that in the top, individuals look like their fathers, whether at the bottom, dewlap colors are intermediate between that of the two populations.

Everybody loves a pretty dewlap, and recent years have seen a lot of interest in studying the factors that determine dewlap color, as well as the role dewlap color may play in species recognition, sexual selection and other processes. Many have suggested that the dewlap is a focus of sexual selection; some have even opined that it is an honest signal of something, maybe good genetic quality, maybe the ability to procure lots of color-inducing dietary items. Unfortunately, we know almost nothing about the genetic basis of dewlap color, nor about the effect of environmental variation.

Anolis distichus exhibits more variation in dewlap color and pattern than any other anole, and thus is the perfect choice for such a study. Julienne Ng just completed her doctoral research at U. Rochester on this species, documenting that variation in dewlap color correlates with environment among populations. Now she and colleagues report on laboratory studies to assess the extent to which variation is determined by genes vs. diet.

Why diet? Because reds and oranges are likely determined by carotenoids, which vertebrates cannot synthesize. Thus, it is plausible that the amount of carotenoids ingested by a lizard may correlate with its color. This hypothesis has only been tested once before, in a study on A. sagrei by Steffen, who failed to find evidence for a diet effect on the red-orange dewlap of this species.

This study had two components. First, to study genetics, lizards from two populations–one with an orange dewlap, the other with a plain whitish dewlap–were crossed in the laboratory. Second, lizards were fed lots of carotenoids.

The results: strong evidence for a genetic basis for variation in dewlap color. Purebred individuals looked like their fathers (top two rows in figure above), but crosses were intermediate in color (bottom two). Pretty strong evidence for a genetic basis for the trait. And the effect of diet? Not so much. No difference in color between lizards in the  carotenoid supplementation treatment vs. the control lizards.

The bottom line is that, at least in this species, genes control variation in dewlap color. Combined with Steffen’s study, there are now two negative results for a role of diet. Of course, work on other species is necessary to confirm the generality of these results, as well as additional investigation into the exact genes responsible for dewlap color.

The long-tailed Asian lacertid lizard, Takydromus sexlineatus. Photo by John White.

Tail loss (aututomy) is one of the more amazing things done by lizards, but for for me it’s a frustrating reality of studying the physiology of sprinting because rough handling (by me when I was a beginning Ph.D. student and now in my lab by some undergrads) results in a lost tail and thus changed locomotor mechanics. But this frustration turned to fascination when I began studying locomotion in Takydromus sexlineatus. This species is pretty special as it holds the distinction of having the longest tail (relative to snout-vent length) of any lizard.

So I had to pull the tail off and measure how locomotion was changed. This then snowballed into studying the effect of autotomy in Anolis carolinensis and then a collaboration with Philip Bergmann to more broadly address how autotomy influences locomotor performance in lizards by using a meta-analysis of the published literature. We showed that longer tails result in a more drastic change in performance for all lizards studied except the two Takydromus species…so we are still left wondering what that huge tail does!

The result was a talk at the World Congress of Herpetology in Vancouver and a publication in Physiological and Biochemical Zoology as part of a special issue on Tail Loss in Lizards, organized by Tim Higham and Tony Russell.

Grass anoles have really really long tails too….I wonder how those tails are used? Convergence between Takydromus and Grass Anoles? E.N. Arnold did a lot of work on Takydromus and hypothesized that the tail aids in grass-swimming. I have observed this species stand up bipedally and use the tail as a prop (like Varanus). Thoughts?

Almost nothing is known about Anolis macrinii, which is a little surprising because it is rather large (nearly 100 mm snout-vent length) and apparently locally moderately abundant. However, it’s small, localized range in Oaxaca, Mexico is no doubt the explanation. In any case, now a bit more is known, thanks to a recent paper by Gunther Köhler and colleagues in Breviora (freely available on the MCZ publications website).

The paper includes a detailed morphological description of the species, as well as notes on natural history and conservation status. Most interesting to me is the sexual dimorphism in dewlap size (males on top above, females below), which we have discussed in previous posts, and the aberrant patterning of one juvenile individual (right).

Here’s the abstract:

During three short visits to the coffee-growing region in the hills north of Pochutla (Oaxaca, Mexico), we observed Anolis macrinii in its natural habitat. The species appeared to be relatively abundant, and we collected 12 individuals, including several adult males. The holotype of this species was reported erroneously to be an adult male but actually is a female. The confusion might have arisen from the moderate-sized dewlap present in adult females. However, males have a very large dewlap and a pair of moderately to greatly enlarged postcloacal scales. We provide color descriptions in life for three individuals, color photographs in life, description and illustration of hemipenis morphology, and some natural history notes. Finally, we discuss the conservation status of this species.