DISSERTATION RESEARCH: Neuroendocrine Mechanisms Underlying Rapid Change in Social Behavior

North Carolina State University, Raleigh NC

Investigators

Abstract

Neuroendocrine mechanisms underlying rapid change in social behavior (0206677) Principal Investigator: John Robert Godwin Doctoral Student: Katharine Anne Semsar Both environmental and internal physiological influences affect the expression of sexual and aggressive behavior by animals including humans. For species that live in unpredictable environments, the appropriateness of displaying sexual and/or aggressive behavior can change quickly. A good deal of research has focused on adaptations to changes in the physical environment, but social environments can be equally unpredictable and it is therefore important that animals be able to adapt their behavior quickly in the face of social change as well. A large body of work over the past twenty years has documented important roles for neuropeptide hormones in mediating social behaviors ranging from mating and parental care to mate guarding and territorial defense. Two neuropeptide hormones found to play especially prominent roles are arginine vasotocin (AVT) in non-mammalian vertebrates and the very similar arginine vasopressin found in mammals (AVP). These hormones are released in the brain and act to alter neural function in areas known to be associated with social behavior. While many studies have shown effects of these hormones on behavior in the laboratory, there are still relatively few studies that have examined the detailed mechanisms by which AVT or AVP affect sexual and aggressive behavior in the full complexity of the natural environment. This study would explore mechanisms by which AVT affects sexual and aggressive behavior and the social and hormonal conditions that determine the nature of the effects of this hormone on these behaviors. The experimental model is the bluehead wrasse (Thalassoma bifasciatum), a well studied sex- and role-changing coral reef fish. Bluehead wrasses exhibit socially controlled female-to-male sex change in which females can become functional males within approximately ten days of becoming socially dominant. This model species has two principal advantages for the type of study proposed. First, the dependence of the sex change process on cues from the social environment makes it a very good system for understanding social influences on neural function and the interaction of environmental and internal hormonal cues in controlling behavior. Second, because of large populations in shallow, protected waters and extraordinary ease of capture for marking and experimental manipulations, bluehead wrasses allow the mechanisms underlying neuropeptide actions to be studied in nature. Previous work by John Godwin has shown that AVT expression increases in the hypothalamus as females begin to exhibit male behavior and their ovaries become testis during sex change. Studies by Katharine Semsar and John Godwin have shown that AVT can induce territorial aggression and courtship behavior in large males who do not hold territories while an AVT receptor blocker can reduce these behaviors in territory-holding males. The studies outlined in this proposal would determine: i) whether AVT is necessary for females to become males behaviorally and whether augmenting AVT can accelerate this process, ii) whether the ability to respond to AVT, as measured by receptors for this hormone, changes during sex change, and iii) what the effects of a potent androgenic hormone that rises during sex change (11-ketotestosterone) are on the expression of AVT and its receptor in the brain. This work should improve our understanding of behavioral adaptation and the role of neuropeptide hormones in these processes. These mechanisms are of strong basic interest, but also important more generally because of the societal costs of aggressive behavior.