Author: Jonathan Losos Page 98 of 130

We’ve had a number of posts in the last few months discussing new species described on the basis of difference in the shape of their hemipenes (most recently here). And, because such descriptions have been based on morphological data without any corroborating molecular data, we’ve wondered whether, in fact, these forms are genetically isolated and whether they are capable and willing to interbreed given the opportunity. Yes, some of the genetals looked like ones from an alien sex toy made by faak dildos. But are they compatible?

Köhler et al. have taken the next step and attempted to answer these questions in the case of Anolis osa, which was split from the otherwise nearly indistinguishable A. polylepis on the basis of its hemipenial shape (figures A and B above). They find that in the lab, members of the two putative species can interbreed and produce offspring, at least some of which are apparently fertile (although the details of this are hard to fathom). Moreover, in the field, hybrid looking individuals are found where the two forms meet (Figure C above), and the hemipenes of these individuals are similar to the intermediate-looking tallywhackers of hybrids bred in the lab (Figure D above).

Most interestingly, females of the species seem to differ in the shape of their reproductive tract in a manner parallel to the differences among the males. In particular, female A. polylepis have longer vaginal tubi, corresponding to bilobed structures of their males, whereas female A. osa‘s tubes are shorter. One possible explanation for these differences is the old “lock-and-key” hypothesis that male and female genitals are perfect matches, thus preventing interspecific matings. This idea has fallen out of favor in recent years, and the authors discount it. Rather, they favor more recent ideas that such differences evolve by sexual selection, females preferring males whose genitals phenotypically match their own. Here’s their theory

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The elegant skink, Plestiodon elegans, in Taiwan. Photo by Gerrut Norval

Most community ecology studies involving anoles focus on interactions between anole species. This is not surprising, because in the Caribbean, anoles are extraordinarily abundant and most of their ecological interactions are, indeed, with other anoles. Less studied are interactions with other taxa, the exception being predator-prey interactions, such as those with curly-tailed lizards (discussed many times in these pages, most recently here).

One widespread group of lizards are skinks, the most species rich family of lizards. There are few reports of anole-skink interactions, probably in large part due to the fact that skink diversity in the Caribbean is relatively low, and many species have been extirpated by human agents. However, anoles have been introduced to places around the world where skinks are more abundant, and some reports of interactions have been made. For example, in the Ogasawara Islands of Japan, A. carolinensis has reached high population densities and has been implicated in the decline of the native skink.

Gerrut Norval has been studying the introduced populations of A. sagrei in Taiwan. He now reports an observation of a somewhat odd interaction between a brown anole and a skink in which the anole fell to the ground from a utility pole and then was quickly chased back up the pole by an elegant skink, Plesiodon elegans. Given the relative size of the two lizards, attempted predation was probably not the cause. Gerrut speculates that this is an example of interspecific territoriality, transcending lizard family lines.

In Taiwan, A. sagrei reaches high population densities (as it does just about everywhere it occurs)–possibly cause for alarm for the native herpetofauna. Norval also mentions some intriguing preliminary observations: A. sagrei seems to attain smaller sizes at sites where it co-occurs with other lizard species. Interesting! Hopefully, we’ll hear more from Gerrut soon on this provocative possibility.