Hormonal correlates of natal dispersal and rank attainment in wild male baboons

Abstract

In many mammals, maturational milestones such as dispersal and the attainment of adult dominance rank mark stages in the onset of reproductive activity and depend on a coordinated set of hormonal and socio-behavioral changes. Studies that focus on the link between hormones and maturational milestones are uncommon in wild mammals because of the challenges of obtaining adequate sample sizes of maturing animals and of tracking the movements of dispersing animals. We examined two maturational milestones in wild male baboons—adult dominance rank attainment and natal dispersal—and measured their association with variation in glucocorticoids (fGC) and fecal testosterone (fT). We found that rank attainment is associated with an increase in fGC levels but not fT levels: males that have achieved any adult rank have higher fGC than males that have not yet attained an adult rank. This indicates that once males have attained an adult rank they experience greater energetic and/or psychosocial demands than they did prior to attaining this milestone, most likely because of the resulting participation in both agonistic and sexual behaviors that accompany rank attainment. In contrast, natal dispersal does not produce sustained increases in either fGC or fT levels, suggesting that individuals are either well adapted to face the challenges associated with dispersal or that the effects of dispersal on hormone levels are ephemeral for male baboons.

Noninvasive measurement of mucosal immunity in a free‐ranging baboon population

“…During this period, which we define as adolescence, males experience a growth spurt, at the end of which males are twice as large as adult females and can agonistically challenge adult males (Altmann & Alberts, 2005). Adulthood is defined by attaining a dominance rank among adult males, which occurs at a median age of 7.45 years in Amboseli (Alberts & Altmann, 1995b; Altmann & Alberts, 2005; see also Akinyi et al, 2017). After attaining an adult dominance rank, males begin to consort (i.e., mate guard) and copulate with females (Alberts & Altmann, 1995b).…”

“…After attaining an adult dominance rank, males begin to consort (i.e., mate guard) and copulate with females (Alberts & Altmann, 1995b). Male baboons also disperse from the natal group; in Amboseli, this may occur before or after they attain adult rank and begin their reproductive lives (Akinyi et al, 2017; Alberts & Altmann, 1995a, 1995b).…”

How individual, social, and ecological conditions influence dispersal decisions in male vervet monkeys

“…An increase in fGCM levels during dispersal was observed in meerkats (A. J. Young & Monfort, 2009), but not in some primates (yellow baboons, Papio cynocephalus : Akinyi et al, 2017; anubis baboons, Papio hamadryas : Bergman et al, 2005; crested macaques: Marty et al, 2017). We also predicted that if natal dispersers emigrate at or around the age of sexual maturity, the dispersal event could be triggered by increased androgen levels associated with reproductive maturation.…”

“…Animals typically disperse at least once (from their natal group), and some species may disperse again after their initial transfer (i.e., secondary or breeding dispersal) (Jack, 2003; Pusey, 1987). For primates, male natal dispersal typically occurs around the age of sexual maturity (Akinyi et al, 2017; Cheney & Seyfarth, 1983; Jack & Fedigan, 2004a). Generally, in species living in multimale groups, natal dispersers have not yet reached their full body size and may therefore not be able to compete with full‐grown adult males when joining a new group; thus, they are more likely to immigrate peacefully at the bottom of the dominance hierarchy, despite fewer reproductive benefits (Jack & Fedigan, 2004a; Pusey & Packer, 1987a).…”

“…Social costs involve moving from one social environment to another and are usually related to the loss of familiar social partners, including kin, and/or aggression from conspecifics in the new social group (Alberts & Altmann, 1995; Cheney & Seyfarth, 1983; Jack & Fedigan, 2004b; Schoof et al, 2009). Furthermore, resident males may experience the emigration of coresidents or the immigration of new males as social stressors associated with social instability (Akinyi et al, 2017; Marty et al, 2017). Both locational dispersal and social costs, alongside other environmental stressors, may lead to an elevated stress response (A. J.…”