Host: Primate Society of Japan
Castration has been used in nonhuman primates to control population demography, but the impact of this procedure on the social relationships of male Japanese macaques living in a complex society has not yet been investigated. This research examined fecal glucocorticoids (fGC) and fecal testosterone (fT) concentrations in male Japanese macaques residing in two social groups of contrasting environments (Jigokudani, Japan and Born Free Primate Sanctuary - BFS, Texas, USA), and males housed individually. The primary goal was to test the effect of castration on dominance hierarchy and steroid concentrations in Japanese macaques. We also investigated social, environmental and biological factors affecting steroid hormones. We collected behavioral data (focal animal and ad libitum sampling) to establish male dominance rank in the social groups, and fecal samples during the non-mating season from all males. We found that males housed in single cages had fT concentrations similar to castrated males and lower than intact social males. Castrated males maintained a dominance hierarchy primarily determined by age, and they were less aggressive than intact social males. Age had a positive relationship with fGC, but the opposite trend on fT levels. Rank and temperature were directly correlated to fT concentrations only in the intact social group. Our findings indicate that testosterone can be a consequence of the social structure of the group, and therefore is significantly affected by the social environment. Our results can contribute to the management and monitoring of primate populations in the wild and in captivity because they reveal that a complexity of connections link the social environment with male Japanese macaque steroid concentrations.
