Anole Annals

Hello once again from the IBS in Miami. As I mentioned in my last post, anole presentations are a little thin on the ground here (though not around the conference centre where, with the help from some locals, we saw sagrei, carolinensis, equestris and distichus today).

I did have the opportunity yesterday to check out the the second of two anole presentations here – a new look at the sub-fossil lizard communities, with a focus on a question familiar to many readers of this blog: What’s the deal with A. pogus on Anguilla?

Has A. pogus ever been on Anguilla? Nope.

The study is being led by Melissa Kemp, from Liz Hadly’s lab at Stanford. Melissa has re-analyzed lizard dentaries from excavations on Anguilla that featured heavily in an anole character displacement versus taxon cycle debate in the early 90s.

By analyzing the size distribution of anole dentaries dating back 10,000 years on Anguilla, Melissa argues that not only is there a lack of evidence for a taxon-cycle involving A. pogus, but that there’s no evidence that A. pogus has occurred (in meaningful numbers) on the island at all! To further test this, Melissa has sequenced a portion of cytochrome b for five specimens thus far, all of which have turned out to be A. gingivinus, with more sequences coming down the pipeline.

Anoles aren’t the only lizards Melissa has uncovered – with Thecadactylus, Ameiva and Leiocephalus all present. Anoles have dominated the fauna in all but the earliest (and sparsely sampled) time slice and Leiocephalus was historically present (but probably not abundant) but disappeared several thousand of years ago and has not reappeared in the sub-fossil record since.

This was my first exposure to sub-fossil analysis of lizard communities and I was definitely impressed. I don’t have a sense of how much similar work there is in the literature (but I’m sure readers of the blog can educate me), but there seems substantial scope to collaborate with zoo-archaeologists to get more specimens and data on past trait variation and anole assemblage composition.

We’ve had a lot of hoohaw in these pages about amber Anolis, but anoles are not the only lizards represented in the Dominican amber fauna. In particular, a number of fine specimens of amber geckos are known from the D.R., as well as from amber deposits elsewhere. One such species is Sphaerodactylus dommeli. Embarrassing as it is to anole aficionados, this specimen has at times been suggested to be an anole, hard as it may seem to confuse such a lowly gecko with something as magnificent as an anole. In any case, Daza et al. have just published a magnificent analysis demonstrating that the specimen is, indeed, a gecko, and providing tips on how to avoid such unwholesome confusion in the future. Moreover, confirmation of the specimens identity will allow it to be used as a calibration point in future molecular studies of Sphaerodactylus phylogeny.

Anolis bicaorum from Utila, Bay Islands, Honduras. Photo by J. Losos.

Will global warming allow the blue-headed anole, A. allisoni, to move into the forest in the Bay Islands? This individual was photographed on Roatan by J. Losos.

Climate warming is a sad reality that environmentally defines our era. Over the next century, conservative estimates suggest that air temperatures will rise about 3° C. One imperative in research is to try to understand how reptiles, whose physiology is tightly linked to thermal environment, are going to be impacted by these increasing temperatures. During a symposium honoring Ray Huey, a leading biologist (and an anologist, to boot!), Michael Logan of Dartmouth College gave a talk on how small-scale estimates of thermal variation, rather than weather stations, yield interesting and perhaps counterintuitive results for how tropical lizards will be impacted by hotter temperatures. Predictions of potential impact to date rely heavily on temperature data gathered from weather stations – those provide a resolution of one square kilometer. For small reptiles, like tropical anoles, he argues that we need a finer resolution. To this end, Logan launched several operative temperature devices (sensors that perceive temperature as a lizard would, rather than just air temperature) on Cayo Mayor and Utila, which are islands in the Bay Island Archipelago in Honduras. We’ve discussed the anoles of the Bay Islands here on our blog before. On Cayo Mayor, Anolis lemurinus is found in the closed-canopy forest, while the blue-headed lizard,  A. allisoni is found in more open habitats. A close relative of A. lemurinus, Anolis bicaorum, is found throughout Utila. Because closed-canopy forests are more thermally homogenous (less variation in available temperatures due to less access to sun and shade patches), the expectation is that, under a scenario of climate warming, the open habitat species A. allisoni should be able to invade A. lemurinus‘ habitat. Logan says that A. allisoni will not invade the forest habitat, although the details of the analysis suggest to me that they might. From what I saw, increasing temperatures in the forest should allow A. allisoni to invade the newly available warm habitat. He does find that A. lemurinus should experience a loss in potential daily activity hours because of increasing temperatures, putting this species at risk. The common species (A. bicaorum) will actually experience more hours of activity and likely benefit, at least in the short term, from increased temperatures. Logan concludes that more micro-scale measurements provide the appropriate resolution for studies of thermal performance in lizards, and will be the wave of the future.