The association of intergroup encounters, dominance status, and fecal androgen and glucocorticoid profiles in wild male white-faced capuchins (Cebus capucinus)

Abstract

Androgens play a role in male reproductive competition, frequently via aggression, while glucocorticoids are associated with the stress response. However, the relationships of these hormones with different sources of competition (intra- vs. intergroup) and dominance status are highly variable. Here, we consider the fecal androgen (fA) and glucocorticoid (fGC) profiles of alpha and subordinate male Cebus capucinus in the context of intergroup competition during a rare period of low intragroup competition (i.e. all females were either pregnant or lactating). Intergroup encounters (IGEs) are a long-term reproductive strategy in male white-faced capuchins, enabling them to assess the composition of neighboring groups. IGEs pose a threat to resident males as these can result in injury or death, loss of dominance rank, group eviction, and group takeovers that are frequently associated with infanticide. From February to July 2007, fecal samples were collected from eight males in three groups of white-faced capuchins in the Santa Rosa Sector of the Área de Conservación Guanacaste, Costa Rica. IGE rate was positively associated with both fA and fGC levels, indicating that IGEs are perceived as reproductive challenges by resident males, and may be associated with elevated metabolic costs. Alpha males sire the majority of group offspring and, accordingly, the threat of IGEs to both future (via rank loss or eviction) and current (via infanticide) reproductive success is greater than for subordinate males. Consistent with this observation, alpha males had higher fA and fGC levels than subordinate males. Given that all females were either pregnant or lactating and pronounced overt intragroup competition was absent, we interpret the difference in hormone profiles of alpha and subordinate males as being primarily associated with variation in the perceived threats of IGEs according to dominance status. Future studies should focus on the interaction of intra- and intergroup competition by examining hormone levels in the presence of periovulatory females.

Figure 1

Log of individual male mean a) fecal androgen and b) fecal glucocorticoid level and seasonal intergroup encounter (IGE) rate (encounters/hour) for each of three social groups

Figure 1

Log of individual male mean a) fecal androgen and b) fecal glucocorticoid level and seasonal intergroup encounter (IGE) rate (encounters/hour) for each of three social groups

Figure 2

Mean male a) fecal androgen and b) fecal glucocorticoid levels (ng/g) across three social groups. Alpha males are indicated with solid bars, and subordinates are indicated by open bars.

Figure 2

Mean male a) fecal androgen and b) fecal glucocorticoid levels (ng/g) across three social groups. Alpha males are indicated with solid bars, and subordinates are indicated by open bars.