Year: 2012 Page 24 of 47

In an epic undertaking, Powell and Henderson have edited a monograph compiling the species occurrence of reptiles and amphibians on more than 700 Caribbean islands. In addition to the species lists, information on island size and location is provided, and introduced and extinct species are noted.

This work, an update on several previous such lists, will be enormously useful for biogeographers, ecologists, evolutionary biologists, and conservationists, among others, and the editors and authors are to be heartily thanked and congratulated for their efforts.

Now, an anole bone to pick.

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Photo by Claus Meyer at http://www.nationalgeographicstock.com/

For many years, the South American lizard genus Polychrus has been considered the closest extant outgroup to Anolis.  In light of this phylogenetic position, the authors of a new report on the life history of Polychrus acutirostris note that “a comprehensive understanding of Polychrus might help clarify possible ecological factors related to the radiation of anoline lizards as well as to infer the existence of niche conservatism or dietary shifts related to the origin of this large lizard radiation” (Garda et al. 2012).

Members of Polychrus are superficially similar to Anolis, and are mostly medium sized arboreal and diurnal lizards.  However, Polychrus also differs from Anolis in both conspicuous (e.g., lack of toepads) and somewhat less conspicuous ways (e.g., its tendency to produce single clutches of multiple eggs, versus multiple one egg clutches in Anolis).  In their report, Garda et al. (2012) compare populations of Polychrus acutirostris found in two different Brazilian habitats to test whether size of eggs and clutch size, reproductive seasonality, diet, and size of reproductive adults varies among populations in the manner predicted by life history theory.  Although recent work makes Polychrus‘s position as the outgroup to Anolis less certain than it once was (Schulte et al. 2003, Townsend et al. 2011, and this previous AA post), we still have much to learn from the type of comparative studies that Garda et al. have implemented.

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Anolis concolor from mangroves on San Andres island. Photo by Lee Fitzgerald

Almost all Caribbean anoles are descendants from a single colonizing species, whose descendants now occupy all of the Greater Antilles, the Lesser Antilles south through Dominica, and many other islands. Almost all of the remaining species are members of the roquet clade, occupying the southern Lesser Antilles and descended from a South American colonist. As we all know, these species have been extensively studied.

But colonization of Caribbean islands has occurred more than just these two times. Some other islands have been colonized by different colonists. None of these invasions has led to much in the way of evolutionary radiation and these species–in each case the only anole on the islands they occupy–have been little studied. We’ve previously discussed one such colonization, A. lineatus on Aruba and Curaçao. In addition, islands in the Pacific (yes, the Pacific!) have twice been colonized, leading to A. agassizi on little known Malpelo and A. townsendi on Cocos Island (incidentally, the island said to have beeen the inspiration for Isla Nublar in Jurassic Park).

And, finally, there are the presumed sister taxa, A. pinchoti and A. concolor, on the Colombian islands of Providencia and San Andrés. A smidgeon of research has been conducted previously on their ecology, and now a new paper in the South American Journal of Herpetology has examined their morphology. Calderón-Espinosa and Barragán Forero measured museum specimens of these species and compared them to published data on a variety of other Caribbean anoles. They found that neither species is a good match for any of the Greater Antillean ecomorphs, but that they are most similar to trunk-ground or trunk-crown anoles. By comparison, anoles of the Lesser Antilles are also most similar to these two ecomorphs. Anolis concolor attains an intermediate body size, similar to Lesser Antillean species that occupy islands on which they are no other anole species. By contrast, A. pinchoti is smaller and more similar to the smaller Lesser Antillean species on two-species islands.

Anoles are renowned for their convergent evolution. Further comparison of the many cases in which anoles have colonized relatively small islands should prove interesting.

M. L. Calderón-Espinosa and A. Barragán Forero (2011). Morphological Diversification in Solitary Endemic Anoles: Anolis concolor and Anolis pinchoti from San Andrés and Providence Islands, Colombia South American Journal of Herpetology