Meeting Abstract

87.1  Thursday, Jan. 7  Rapid Activation of the Reproductive Axis During Social Ascent MARUSKA, KP*; LEVAVI-SIVAN, B; FERNALD, RD; Stanford Univ; Hebrew Univ maruska@stanford.edu

Reproduction is arguably the most important event in an animal’s life, and social interactions can have profound effects on fertility via the brain-pituitary-gonad (BPG) axis. In an African cichlid fish, Astatotilapia burtoni, reproductive capacity is controlled by the social environment where males reversibly switch between dominant and subordinate status. Dominant males defend territories and court females, have large GnRH1 neurons, high androgen levels, and large testes, while subordinate males do not show dominance behaviors and have a suppressed BPG axis. Prior work showed a suite of differences between stable dominant and subordinate phenotypes, but little is known about the timeline of changes during social transition, and nothing is known about changes at the level of the gonadotropins. Here we induced suppressed males to rise in status, and then measured the resultant changes in behavior and physiology at various times after ascension. Subordinate males increased dominance behaviors within minutes, but decreased territorial and increased reproductive behaviors over subsequent days as they established a territory. There was a rapid increase in pituitary mRNA and circulating plasma levels of the gonadotropins luteinizing hormone (LH) and follicle stimulating hormone (FSH). FSH receptor levels in the testis were also rapidly elevated, while increased LH receptor levels were not detected until 3 days after ascension. Changes in testis cell composition were detected at 3 days, but testicular size was not greater until 5 days. Subordinate males also retain sperm and can successfully spawn within hours of social opportunity. Our results suggest that BPG axis activity is decoupled from both behavior and the ability to reproduce as an adaptation for rapid transition to dominance in a dynamic social environment.