KINSHIP, FAMILIARITY AND MATING AVOIDANCE IN BARBARY MACAQUES, MACACA-SYLVANUS

Long-term data on sexual behaviour in Barbary macaques revealed a strong mating inhibition between co-residing maternal relatives, and between those, mostly unrelated, males and females with a caretaking relationship during the female's infancy. Sexual interactions were observed in only 15 out of 371 possible maternal dyads. There was a bias towards distant kin and towards dyads in which the male was older than the female. Sexual interactions were recorded in only two out of 14 former caretaking dyads with a strong relationship but in 10 out of 17 dyads with a weak and/or temporary relationship. Unfamiliar maternal relatives and paternal relatives showed no mating avoidance. Three out of four of these maternal dyads, and 67 out of 133 possible paternal dyads became incestuous. Paternity was determined by DNA-fingerprinting. Almost all paternal dyads became incestuous after more than 2 years of co-residence. Owing to high sexual activities outside the period of conception and the inability of related and unrelated males to monopolize access to fertile females, only two out of 62 potentially inbred infants were actually inbred via the paternal line. Establishment of a mating inhibition but also its absence in some individuals indicated that only familiarity during early life, regardless of genetic relatedness, was responsible for mutual sexual indifference. This mental mechanism of inbreeding avoidance is regarded as an important trigger for male natal migration.