Sociodemographic Correlates of Fecal Androgen Levels in Wild Male White-Handed Gibbons (Hylobates lar)

Despite the central role of testosterone in influencing many aspects of the male life cycle, information on the influence of social and behavioral factors associated with androgen output is available for only a few primate species, mainly those living in multimale–multifemale societies. We collected 322 fecal samples and measured fecal testosterone metabolite levels in 19 adult male white-handed gibbons (Hylobates lar) from 13 groups living in the Khao Yai National Park, Thailand, to examine the extent to which androgen output is related to sociodemographic variables (social organization, social status, presence of infants, age) in a socially flexible species, i.e., pair-living/multimale groups. We predicted that androgen levels would be higher in males 1) that live in potentially more unstable single-male/single-female units; 2) that are primary (dominant) vs. secondary; 3) that live in groups with dependent infants; and 4) that are of prime vs. senior age. We found marked differences in androgen levels among males and a significant effect of time of the year. Males living in pairs exhibited significantly higher androgen concentrations vs. males living in multimale groups, and males residing in groups with infants showed a significant increase in androgen levels throughout the sampling year. However, we found no relationship with male age or social status. The increased androgen output found in both pair-living males and those residing with infants might be a physiological mechanism that facilitates male aggression to cope with potential threats posed by social challenges and the demand for infant/group defense, respectively. More generally, our data indicate that in socially flexible species male androgen output is less strongly linked to key life-history variables than in species that live permanently in multimale–multifemale groups.