Manipulations of the AVT system shift social status and related courtship and aggressive behavior in the bluehead wrasse

Arginine vasotocin (AVT) and its mammalian homologoue arginine vasopressin (AVID) influence male sexual and aggressive behaviors in many species. We t ested the effects of AVT and an AVP-V-1a receptor antagonist on the display of alternative male tactics in a tropical coral reef fish, the bluehead wr asse Thalassoma bifasciatum. We gave AVT injections to territorial and nont erritorial males of the large and colorful phenotype (terminal phase) and a n AVP-V-1a receptor antagonist, Manning compound, to territorial males in t he field. AVT increased courtship independent of status, while its effects on territoriality and aggression were dependent upon male status. In territ orial males, AVT increased courtship and tended to decrease the number of c hases toward initial phase individuals. In nonterritorial males, AVT increa sed courtship, chases toward initial phase individuals, and territorial beh avior while decreasing feeding. These are all behaviors rarely seen in nont erritorial males, so AVT made these males act like territorial TP males. Th e AVP-V-1a receptor antagonist had opposite effects. It decreased courtship and territorial defense, making these males act more like nonterritorial m ales. Manipulations of the AVT system shifted males within a single phenoty pe from the nonterritorial social status to the territorial social status a nd vice versa. Since the entire suite of behaviors related to territorialit y was affected by AVT system manipulations, our results suggest that the AV T system may play a key role in motivation of behaviors related to mating. (C) 2001 Academic Press.