Hormonal mechanisms regulating alternate phenotypes

by 1974- Semsar, Katharine

SEMSAR, KATHARINE. Hormonal Mechanisms Regulating Alternate Phenotypes. (Under the direction of Dr. John Godwin and Dr. John Vandenbergh.) When social environments are unpredictable, individuals must be able to adapt to these changes by rapidly modifying their behavior. Since these behavioral responses are likely to involve rapid actions of neuropeptides in the brain, understanding these pathways is crucial to an understanding of how animals adapt to their social environment. The bluehead wrasse (Thalassoma bifasciatum) is an excellent model system for approaching these questions for many reasons. Primarily socially-controlled female-tomale sex change naturally decouples the brain from gonadal influences and can be exploited to more directly examine other influences, such as social interactions, on the neural substrates of reproductive behavior. Arginine vasotocin (AVT) and its mammalian homologoue arginine vasopressin (AVP) influence male sexual and aggressive behaviors in many species. To test the effects of AVT on the mediation of male behavior, we gave AVT injections to territorial and non-territorial males of the large and colorful phenotype (terminal phase) and an AVP-V1 receptor antagonist to territorial males in the field. In territorial males, AVT increased courtship and tended to decrease the number of chases towards initial phase individuals. In non-territorial males, AVT increased courtship, chases towards initial phase individuals, and territorial behavior while decreasing feeding, all behaviors rarely seen in non-territorial males. The AVP-V1 receptor antagonist had opposite effects. It decreased courtship and territorial defense, making these males act more like nonterritorial males. These experiments demonstrated that manipulations of the AVT system shifted males within a single phenotype from the non-territorial social status to the territorial social status and vice-versa. Additionally, we examined the role of social and gonadal inputs on the AVT system in the preoptic area (POA) of the hypothalamus. In one experiment, we found that AVT mRNA abundance is higher in sex-changing females who attain social dominance and display dominant male behavior than in subordinate females, regardless of whether the dominant females were intact or ovariectomized. However, AVT-ir soma size in the gigantocellular POA (but not magnocellular or parvocellular POA) increased only when females were both displaying dominant male behavior and had developed testes. In a second experiment, castration of dominant terminal phase males had no effect on AVT mRNA abundance or any behavior we measured but did increase gPOA AVT-ir soma size compared with sham-operated controls. In the third experiment, implants of11-ketotestosterone (11KT), the potent teleost androgen, in socially subordinate, ovariectomized females had no effect on either AVT mRNA abundance or AVT-ir soma size compared with controls. These results demonstrate that AVT neural phenotype in the bluehead wrasse can be strongly influenced by social status and these social influences can be manifested independent of gonads. Furthermore, we examined the roles of AVT and 11KT in mediating sexual and aggressive behaviors typical of dominant males. We demonstrated that AVT appears necessary for the assumption of dominant territorial status in males and females, but is not sufficient for the display of male behavior in females or initial phase males. Finally, treating females with 11KT did not alter responsiveness to AVT, but did induce male coloration and courtship behavior that was not observed in oil-treated females. Together these results indicate that the ability of AVT to induce male-typical behavior differs among sexual phenotypes and that this differential responsiveness appears to be mediated by social context and not directly by exposure to 11KT. S ince 11KT can induce courtship behavior in females that is not affected by AVT, there may be different hormonal mechanisms mediating courtship behavior under different social contexts.