THE BEHAVIOR AND ENDOCRINOLOGY OF DOMINANCE IN FEMALE WHITE-FACED CAPUCHIN MONKEYS (CEBUS CAPUCINUS IMITATOR) IN SECTOR SANTA ROSA, ÁREA DE CONSERVACIÓN GUANACASTE, COSTA RICA

Abstract

The relationship between behavior, hormones and the environment has long been of interest to evolutionary biologists and biological anthropologists. Hormone levels vary between individuals, seasonally, and affect behavior. Research in male mammals shows dominance rank is related to androgen and cortisol levels, both of which vary with breeding season. However, even though females also produce androgens and they play a crucial role in regulating the female reproductive system, the role of androgens in the behavior of females is not well understood. White-faced capuchins (Cebus capucinus imitator) are female philopatric, medium-sized Neotropical monkeys. We characterize dominance in female white-faced capuchins, examine how rates of agonism vary with social and environmental change, and investigate the hormonal underpinnings of behavior in Sector Santa Rosa, Área de Conservación Guanacaste, Costa Rica. We find that females demonstrate only moderately linear dominance hierarchies, likely due to high kin-relatedness between females. We determined nearly the same hierarchy despite the methodology used to determine the rank order. Rates of agonism varied with dominance rank and fruit availability and we suggest that females inherit their rank from their mother, but use agonism to maintain this rank throughout their lives. Females adjust their rates of agonism such that they exhibit greater rates of agonism when ripe fruit availability is low. We propose that females need to increase agonism in order to gain access to sufficient resources to sustain themselves and their reproductive requirements. We also suggest that higher fruit availability leads to fewer bouts of agonism because there is enough fruit to occupy most group members. Higher-ranking females exhibit higher androgen and cortisol levels. This is inconsistent with the dual-hormone hypothesis, which suggests that higher-ranking individuals have higher androgen, but lower cortisol levels. It is possible that the threat of male takeovers leads to higher stress and thus higher levels of cortisol as the threat of infanticide remains present. Androgen and cortisol levels did not vary seasonally with fruit availability. This work advances our understanding of the relationship of behavior, hormone levels and environmental changes and is especially important for a growing understanding of androgens in female primates