Date of Award

5-2017

Document Type

Thesis open access

Department

Biology

First Advisor

Michele A. Johnson

Abstract

Steroid hormones have a well-studied influence on behavior, but circulating levels of testosterone alone cannot fully predict levels of social, androgenic behaviors. Androgen receptor (AR) expression may bridge the gap between circulating androgens and the muscles that control social behavior: species with higher rates of behavior should have higher levels of AR protein in the nuclei of the muscles that control these behaviors. In anole lizards, the ceratohyoid (CH) muscle extends the dewlap, a colorful throat fan used in social displays, and the retractor penis magnus (RPM) muscle retracts the intromittent organ after copulation. I observed social behavior in the field and measured AR protein in the nuclei of the CH and RPM in male lizards of six anole species native to the island of Hispaniola: Anolis chlorocyanus, A. coelestinus, A. brevirostris, A. distichus, A. cybotes, and A. longitibialis. I used immunocytochemistry to measure muscle AR in each of ten individuals per species, and calculated species averages for AR expression. In the field, male anoles of these species showed substantial variation in both their average rate of dewlap display and their observed rate of copulation. I found that lizard species with higher rates of dewlap displays have marginally more AR in the muscle that controls these same dewlap extensions, but found no support for such a relationship in the copulatory system. Furthermore, there was no relationship between AR expression in one muscle and AR expression in the other. These results suggest that AR expression is independently controlled in muscles that control different social behaviors.

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