WINGFIELD, J.C.*; SOMA, K.K.: Autumn and Spring Territoriality: Same Behavior, Different Mechanisms

Vertebrates show a diverse array of social behaviors associated with territoriality. The mechanisms by which these behavioral patterns are regulated by hormones are diverse. Field and laboratory experiments indicate that general underlying themes – possibly mechanisms – do exist. For example, in birds, testosterone activates a type of aggression, territorial behavior, in those species that are territorial only during the breeding season. Territoriality at other times appeared to be independent of gonadal hormone control. One obvious question is – why thisdiversity in control mechanisms ? Control of testosterone secretion during the breeding season must balance the need to compete with other males and provide parental care. Regulation of these behaviors by testosterone in the non-breeding season may incur substantial costs. The male song sparrow (Melospiza melodia morphna) of western Washington State, is sedentary and defends territories in both breeding and non-breeding seasons. Dominance interactions, territorial aggression and song during the non-breeding season are essentially identical to those during the breeding season. Although in the non-breeding season plasma testosterone and estradiol levels are very low, treatment with an aromatase inhibitor decreases aggression and simultaneous implantation of estradiol restores territorial behavior. These data suggest that the mechanism by which testosterone regulates territorial behavior at the central cell level remains intact throughout the year. How the hormonal message to activate such behavior gets to the brain in different season does, however, appear to be different.