Staying put or leaving home: endocrine, neuroendocrine and behavioral consequences in male African striped mice

Social flexibility occurs when individuals of both sexes can change their social and reproductive tactics, which in turn can influence the social system of an entire population. However, little is known regarding the extent to which individuals of socially flexible species vary in their social behavior and in the underlying physiological mechanisms that support different social tactics. The present study in African striped mice modeled in captivity three male tactics described from the field: (a) philopatric males remaining in the family; (b) solitary roamers; or (c) group-living breeding males. Sixteen pairs and their offspring were kept in captivity, while one male offspring from the family remained as singly housed after he reached 21 days of age. Differences in behavior, morphology, hormone and neuropeptide levels were tested, and physiological measurements were correlated with behavioral measurements. In standardized arena experiments group-living males (philopatrics and breeders) were significantly more aggressive than singly housed males, in agreement with previous data suggesting that group-living, but not roaming males, are territorial. Philopatric males showed signs of reproductive suppression, small testes, lower testosterone and higher corticosterone levels than their singly housed brothers. Higher levels of arginine vasopressin (AVP) were measured in the PVN and BNST of singly housed males compared to group-living males. Based on these findings we hypothesize that roamers are physiologically primed, and capable, if the opportunity to mate arises, to release AVP, form social bonds and become territorial, thus quickly adopting the tactic as breeding male which would yield a higher reproductive success.