Image from Michele Johnson.

Image from Miguel Webber.

Frequent readers of Anole Annals are likely to recall the amazing convergent evolution of morphology related to habitat use in Caribbean anoles that coincides with similarly striking convergent evolution of social behavior. Most of what we know about behavior of Caribbean anoles is how males behave: there are major differences among ecomorphs in how often males use their colorful dewlaps and how often they mate with females. Such male-typical behavior seems intuitively linked to species differences in testosterone signaling. Previous work has shown, though, that these differences do not seem to be related to levels of testosterone in the blood, so Miguel Webber of Michele Johnson’s lab at Trinity University examined whether the receptors for testosterone varies in a manner consistent with the behavior for six Dominican Republic species of anoles and one U.S. species.

Hormones can only cause effects on tissues that have receptors for them, so Miguel looked at receptors for testosterone (androgen receptors) in the muscles responsible for moving those fabulous dewlaps (the ceratohyoid muscle), expecting to find a correlation across species between the number of androgen receptors in the muscle and the rate of dewlap extensions. Although the data are still preliminary, there was a trend for males with higher dewlap extension rates to have more androgen receptors in the ceratohyoid muscle. His next steps are to look for an association between rates of copulation and androgen receptors in the muscle used by males to copulate (retractor penis magnus muscle – yes, it does what you would guess based on the name…). He also wants to see if there is a correlation among species in the behavioral traits and androgen receptors in regions of the brain that are important for social behavior regulation.

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