BURMEISTER, S.S.; JARVIS, E.D.; FERNALD, R.D.; Stanford University; Duke University; Stanford University: Rapid Response of the Preoptic Area to Social Opportunity

Social interactions regulate many aspects of behavior and physiology. In the cichlid fish, Haplochromis burtoni, social dynamics among males determine whether an individual male becomes territorial or non-territorial, two phenotypes that differ in body coloration, behavior, and reproductive capacity. Phenotype is labile and reversible. When males change phenotype, their behavior and coloration change first followed by changes in reproductive physiology. For example, 3 days after a male becomes territorial, his gonadotropin-releasing hormone (GnRH) neurons increase expression of GnRH. We developed a behavioral paradigm of phenotype change that allows us to measure rapid transitions from non-territorial to territorial phenotype. We sacrificed males 20 min after they first displayed territorial behavior during a transition to the territorial phenotype and used in situ hybridization to quantify expression of the immediate-early gene transcription factor egr-1 in the GnRH-containing region of the preoptic area (POA) as a measure of neuronal activity. We found that non-territorial males changed their behavior and coloration within 2-14 min of an opportunity to become territorial and this was accompanied by a rapid two-fold induction of egr-1 expression in the GnRH-containing POA relative to stable territorial and non-territorial males. Stable territorial and non-territorial males had similar and low levels of egr-1 expression despite differences in behavior that are characteristic of their phenotype. Our results suggest that the increase in egr-1 expression is a response to a change in phenotype rather than to the production of territorial behaviors. The induction of egr-1 in the POA may represent the initiation of a cascade of molecular events that leads, ultimately, to an increase in reproductive capacity.