Rank effects on social stress in lactating chimpanzees

• Published in: Animal behaviour Vol. 87; pp. 195 - 202
• Main Authors: Markham, A. Catherine, Santymire, Rachel M., Lonsdorf, Elizabeth V., Heintz, Matthew R., Lipende, Iddi, Murray, Carson M.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.01.2014; Harcourt Brace Jovanovich Ltd
• Subjects: Animal behavior; Behavioral biology; chimpanzee; Gombe National Park; lactation; Metabolites; Monkeys & apes; Pan troglodytes; Pan troglodytes schweinfurthii; rank status; stress; Tanzania; Gombe National Park; rank status; stress; chimpanzee; Pan troglodytes schweinfurthii; lactation
• ISSN: 0003-3472; 1095-8282
• DOI: 10.1016/j.anbehav.2013.10.031

Given the deleterious consequences associated with chronic stress, individual differences in stress susceptibility can have important fitness implications. These differences may be explained in part by dominance status because high rank is typically associated with decreased aggression and improved nutrition. Here, we examined the relationship between dominance and social stress in lactating chimpanzees, Pan troglodytes schweinfurthii, at Gombe National Park, Tanzania. We did so by pairing daily demographic and behavioural data with faecal glucocorticoid metabolite (FGM) concentrations collected over 37 months. While there was no main effect of rank, interesting differences emerged by adult subgroup size and adult sex ratio (males/females). We found that differences in FGM concentrations between high- and low-ranking females were most pronounced as adult subgroup size and sex ratio increased. Low-ranking females had higher FGM concentrations in larger subgroups and in subgroups biased towards adult males; we observed no comparable change in FGM concentrations amongst high-ranking females. Because low-ranking females were the recipient of significantly more male aggression relative to females of high rank, these patterns may be driven by psychosocial stress in low-ranking females. There was no significant change in diet quality across subgroup sizes; this finding suggests that nutritional stressors were not driving differences in female FGM concentrations. Being susceptible to social stress has important fitness implications as it may constrain low-ranking females from ‘choosing’ optimal subgroups to take advantage of food resources and/or for the socialization of their offspring. •We examined the relationship between dominance rank and social stress in wild lactating chimpanzees.•Rank differences in faecal glucocorticoid metabolite (FGM) concentration (low>high) increased with subgroup size.•Rank differences in FGM concentration (low>high) increased in male-biased subgroups.•These patterns may be driven by psychosocial stress in low-ranking females.•Our results suggest that FGM concentration in lactating females is not nutritionally driven.