Hormonal Mechanisms Regulating Alternate Phenotypes.

Abstract

In the bluehead wrasse (Thalassoma bifasciatum), socially-controlled female-to-male sex change naturally decouples the brain from gonadal influences. This makes bluehead wrasses an excellent model for examining non-gonadal influences, such as social interactions, on the neural substrates of reproductive behavior. For my dissertation, I sought to further understand the role of AVT (a neuropeptide known to influence sexual and aggressive behaviors) relative to social context, gonadal input, and androgen influences in the mediation of the development and maintenance of male-typical behavior in this species. I examined these relationships by manipulating hormone levels and social context in the field and analyzing both the behavior and AVT neural phenotypes resulting from these manipulations.

We found that changes in AVT neural phenotype are largely dependent on social influences not on gonadal input. In addition, AVT is necessary for both females and terminal phase (TP) males to display dominance on a spawning site. However, the ability of AVT to override social cues to induce male-typical behavior under conditions of social inhibition appears to be phenotype dependent. In the initial phase phenotype (either female or male) AVT treatment cannot induce male-typical territorial behavior. In contrast, in the TP phenotype, manipulations of the AVT system alone can override environmental cues to shift individuals between non-territorial and territorial social status. Finally, treating subordinate females with 11-ketotestosterone (11KT), a potent teleost androgen, induced male coloration and low levels of opportunistic courtship behavior typical of non-territorial males but did not alter responsiveness to AVT treatment. Together these results suggest there may be different hormonal mechanisms mediating courtship behavior under different social contexts.