LYNCH, Kathleen S.; WILCZYNSKI, Walter; University of Texas, Austin: Plasticity in Female Mate Choice is Associated with Natural Fluctuations in Gonadal Steroid Levels

Females are capable of expressing plasticity in their mate choices. Such plasticity can arise as a consequence of intrinsic factors that influence behavior. One such factor is gonadal hormones. We examined female mate choice plasticity throughout the course of a single breeding season and measured corresponding gonadal hormone levels. We predicted that changes in mate choice decisions would correspond to natural fluctuations in estrogen, progesterone and/or testosterone. Mate choice behavior and hormone concentrations were measured at three points during the breeding cycle; unamplexed (before mate selection occurs), amplexed (near the point of oviposit) and post-mated (after egg release). Our results show that female tungara frogs (Physalaemus pustulosus) are more motivated to mate as they approach the time at which they will release their eggs. This increased motivation to mate is associated with a decrease in mate selectivity, so that females display a broader range of mate signals that are acceptable to them. The decrease in selectivity, however, is not due to a decrease in the female�s ability to discriminate. Furthermore, these behavioral changes do correspond to significant changes in gonadal hormone concentrations. There is a peak in both estradiol and progesterone levels (P = 0.02 and P < 0.001, respectively), that occurs during the amplexed stage, which is the point closest to when egg release will occur. These levels significantly decline ten days after the female has released eggs. The concurrent change in gonadal hormone levels and mate choice behavior suggest that the female�s physiological state while searching amongst potential mates can play a role in the outcome of her mate decision.