Infanticide by resident males and female counter-strategies in wild Japanese macaques (Macaca fuscata)

Infanticide was observed for the first time in a wild, non-provisioned troo p of Japanese macaques on Yakushima Island, Japan. Eight adult resident mal es attacked unweaned infants in the pre- and early mating season, and one i nfanticide was observed directly. These attacks were not consistent with th e social pathology, side effect of male aggression, cannibalism, or the res ource defense hypothesis, but were generally consistent with the sexual-sel ection hypothesis, First, most male attackers had risen in dominance rank b ecause several high-ranking males had left the troop. Second, in 78% of cas es, male attackers had not previously been observed to mate with the mother s of victims, Moreover, analysis of subject animal DNA showed that males di d not attack their own offspring. The two mothers who lost their unweaned i nfants, however, were not subsequently observed to mate. In fact, almost no mating behavior was observed in the troop. This was most likely due to a p oor fruiting year. Resumption of mating by females who lost their infants m ay have been inhibited by an intervening environmental variable which suppr essed female reproductive function. These observations contribute to a grow ing body of evidence which suggests that sexually selected infanticide can occur in seasonally breeding, multi-male, multi-female primate groups. Fema le Japanese macaques are known to mate with multiple males. We found eviden ce that female mating with multiple males inhibits contact aggression towar ds their infants. Adult males attacked infants eight times more often when they had not previously mated with the mother.