Environmental and genetic causes of maturational differences among rhesus macaque matrilines

Females of many cercopithecine primates live in stable dominance hierarchies that create long-term asymmetries among sets of female relatives (matrilines) in access to limiting resources and shelter from psychosocial stress. Rank-related differences in fitness components are widely documented, but their causes are unclear. Predicted breeding values from an animal model for female age of first reproduction are used to discriminate between shared additive genetic and shared environmental effects among the members of matrilines in a population of free-ranging rhesus macaques (Macaca mulatta). While age of first reproduction has a modest heritability (≈0.2), breeding values are distributed in a largely random fashion among matrilines and contribute little to the observed rank-related differences in average age of first reproduction. These results support the long-held, but previously unverified, contention that rank-related life history differences in female cercopithecine primates are the result of environmental rather than genetic differences among them.