PARIKH, Victoria N; SCHRUMPF, Mark; CLEMENT, Tricia; FERNALD, Russell D; Stanford University; Stanford University; Stanford University; Stanford University: The Regulatory Effects of Cortisol on Social Status Shift in Haplochromis burtoni

The social paradigm of the African Cichlid Fish, Haplochromis burtoni, provides an opportunity to study the interaction of social environment and physiology as they relate to social status. Two distinct phenotypes of H. burtoni males exist. Territorial (T) males are dominant in the social hierarchy, are brightly colored, and reproductively active. Non-territorial (NT) males are submissive and reproductively inactive. Male fish shift between phenotypes depending on social environment. Phenotype shifts are gradual. Social ascent (NT to T) takes one week while descent takes three weeks. Higher cortisol levels have been reported to be correlated with NT status. To explore the possible role of cortisol in the transition between these status-dictated phenotypes, we manipulated plasma cortisol level and evaluated its regulatory effects on the behavioral and physiological correlates of social status. In one week trials, T males exposed to elevated cortisol had a typical NT behavioral reaction to an aggressive stimulus, whereas control animals showed typical T behavior. Also, GnRH1 expression was lower in cortisol implanted males (again characteristic of NT status). In two week trials, the behavioral reaction of cortisol treated animals continued to resemble NT males. A marked increase in GSI difference across groups also appeared in the two week trials as compared to one week data. These findings indicate that T males with elevated plasma cortisol show both behavioral and physiological correlates of NT state that increase in a graded fashion over a two week period, just as is seen in socially-dictated status shifts. Given this behavioral and physiological remodeling, we conclude that elevated plasma cortisol is not only descriptive of an NT state, but is also causative.