Female Anolis polylepis. Photo from http://www.wildherps.com/species/A.polylepis.html

In many species of anoles, females within a population exhibit sometimes strikingly different back patterns. A recent paper showed that there is interesting variation in the incidence of such variation: mainland and Lesser Antillean anoles exhibit it much more than Greater Antillean anoles, and within regions, some clades are more polymorphic than others. Although closely related species tend to be similar, this trait has been evolutionarily labile, evolving an estimated 28 times.

The occurrence of this variation raises the question: what’s it for? The most detailed study of the question was Schoener and Schoener’s examination of female polymorphism in Anolis sagrei in the Bahamas. By looking both within and between populations, they concluded that this polymorphism was related to crypsis. In particular, females with stripes tend to occur on narrow diameter branches, where the stripes help them blend in. Calsbeek and Cox have more recently examined the same species, finding most recently that different patterns don’t seem to vary in fitness, though they did not examine whether females with different patterns occurred in different parts of the microhabitat.

The only other recent work on this topic was conducted on A. polylepis in Costa Rica by Steffen. This paper was published in IRCF Reptiles & Amphibians (always a source of not only sumptuous photographs, but copious information on anoles) and may be downloaded here. Steffen found that three female back patterns occurred in the population he studied (see above) and that the types differed in how high they perched above the ground.

These differences are not related to any other attributes of the females (e.g., size, gravidity), and the three pattern types did not differ in the diameter of the structure upon which they were perched. Steffen suggests that crypsis may be involved in this pattern, but calls for more research to understand how these different patterns might be related to crypsis at different heights in the vegetation. More generally, given the great extent of female pattern polymorphism, this would seem to be a subject easily suitable for more research, the most obvious simply being to document whether a relationship exists between pattern type and habitat use in other species.

Jonathan Losos
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