SCOBELL, S.K.*; KNAPP, R.; Univ. Oklahoma, Norman: Hormonal and morphological correlates of reproductive state in the sex-role reversed Gulf pipefish

Little is known about the hormonal mediation of female competitive aggression (e.g., Staub and DeBeer 1997). One possibility is that similar hormones mediate aggressive behavior in females and males. Previous studies of male aggression have shown that androgens in particular can mediate aggressive and sexual behaviors. Alternatively, different hormones than those that are behaviorally active in males could mediate female aggression. For example, estradiol has been shown to mediate aggressive interactions between female lizards (Woodley and Moore 2000). Ideal situations in which to study the physiological mechanisms underlying female aggression are sex-role reversed species in which females compete with each other for access to mates and males are choosy. The Gulf pipefish, Syngnathus scovelli, is believed to be such a species (Jones and Avise 2001). As a first step in understanding this system, we are working to identify the hormones that are likely candidates to mediate reproductive behaviors in this species. We collected hormone and morphological data from adult female and male Gulf pipefish in various stages of reproduction. Several body size measurements were correlated within each sex, including body length, body mass and body depth. In females, a striped banding pattern believed to be a secondary sexual characteristic was categorized according to coloration and completeness of the bands. Only females with the strongest banding pattern had ovaries with large, mature eggs. We thus hypothesize that the same hormones that mediate oocyte maturation mediate expression of the female banding pattern and, in turn, female competitive aggression for mates. We are currently measuring plasma hormone levels for these animals to test this hypothesis.