SEX-DIFFERENCES IN MORTALITY OF JAPANESE MACAQUES - 21 YEARS OF DATA FROM THE ARASHIYAMA WEST POPULATION

Theorists argue that mortality in male mammals should be higher than t hat of females, and many studies of primates followed across the life course have found this to be the case. This study examines mortality p atterns in the rapidly expanding Arashiyama West (Texas) population of Japanese macaques (Macaca fuscata) and finds that males have a signif icantly lower median survival age (12.2 years) in comparison to female s (20.5 years). Males and females are born in equal proportions, but b y adulthood there are 2-5 females to every male. Males are at higher r isk of falling victim to infectious diseases and human-related causes of death, and they are more likely to ''disappear'' from the populatio n, which is inferred to result largely from emigration. There are no s ignificant sex differences in the risks of dying from predation, non-i nfectious illnesses, neonatal defect, or social stress. Males become m ore susceptible to mortality than females once they reach sexual matur ity, and they remain at greater risk than females until their old age. There is no evidence that one sex or the other is at greater risk of dying as infants, or as juveniles. Comparing males of different age cl asses, adolescent and adult males are more likely to die and to disapp ear than are juvenile males. These findings support the ''high-risk, h igh-gain'' hypothesis that males are mainly lost to the population bec ause of their risk-taking behaviors after sexual maturity, rather than the ''fragile male'' hypothesis that males are more vulnerable to mor tality during the period of growth and development. (C) 1997 Wiley-Lis s, Inc.