DISSERTATION RESEARCH: Androgen regulation of territorial male-typical behavior and neuropeptide gene expression during socially-induced sex and role change in a coral reef fish

The ability to respond and adapt to current environmental or social condition, depends to a large extent of the flexibility to make behavioral, physiological and neurological changes. An area of great interest is the plasticity of the brain to change in response to new challenges. One of the greatest examples of this ability is seen in fish that are capable of switching from female-to-male or male-to-female either behavioral or phenotypically. This occurs when changes in the population, loss of males or females increase the ability to reproduce by changing. In species with socially-controlled sex change and/or role change, the brain perceives alterations in the social environment that indicate it is favorable for these changes and therefore 'permissive'. This is observed in the bluehead wrasse (Thalassoma bifasciatum), a Caribbean coral reef fish with a lek-like mating system in which territorial-terminal phase (T-TP) males defend spawning territories for access to females and breed with multiple females. Removal of a T-TP male from a spawning territory creates a permissive environment that induces sex change in the largest female or male role change in the largest non-territorial male, either an initial phase (IP) male or non-territorial-terminal phase (NT-TP) male. This research will examine the role androgen hormones in response to changing social influences to promote behavioral and phenotypic changes. These types of studies are important as they have the ability to demonstrate the constraint of social interactions and the brains ability to change to when constraints are left or there are major changes in the environment.

Within minutes-to-hours of removing a bluehead wrasse T-TP male from its territory, changes in the brain of the largest female, IP male, or NT-TP male induce T-TP male-typical behaviors, such as courtship of females and agonistic behavior directed at other males. Changes in the brain also activate the hypothalamo-pituitary-gonadal (HPG) axis, causing transformation of female ovaries or IP male testes into TP male testes. Androgen production, particularly of 11KT, rises during gonadal transformation in both females and subordinate males during sex and role change. While previous studies show 11KT increases are not necessary for behavioral changes, other observations nevertheless suggest this androgen may play an important role. The neuropeptide vasotocin (homologue of vasopressin in mammals) appears responsible for early behavioral changes. However, could the presence of 11KT induce earlier onset of behavioral changes and increase the display of T-TP male-typical behaviors? NT-TP males have higher baseline levels of 11KT than IP males and females and appear to transition into the role of T-TP male faster. Is 11KT responsible for faster role change? The researchers hypothesize that 11KT promotes behaviors and gene expression profiles typical of T-TP phase males under permissive social conditions. Using a combination of capture/tag-and-release/recapture approaches, hormonal manipulations via gonadectomy and 11KT implantation, behavioral observations of tagged individuals, 11KT serum assays, and gene expression analysis via qRT-PCR, this study will test whether 1) significant differences exist in the timing, frequency, and duration of T-TP male-typical behaviors among females, IP males, and NT-TP males undergoing sex and role change under permissive conditions, 2) gonadal presence affects T-TP male-typical behaviors and gene expression of the vasotocin system and two other neuropeptide systems, kisspeptin and gonadotropin-releasing hormone, during sex and role change, and 3) 11KT promotes T-TP male-typical behaviors and gene expression of these neuropeptide systems during sex and role change. This study will help determine whether 11KT confers an advantage for individuals competing to become the territorial phenotype