Jutta Kuester

Dominance, kinship and reproductive value in female Barbary macaques (Macaca sylvanus) at Affenberg Salem

SummaryIn the course of a long-term study on social organization of semi-free-ranging Barbary macaques (Macaca sylvanus) at Affenberg Salem, genealogical and cross-genealogical rank relations of adult and adolescent females in three social groups were studied. Female rank was highly dependent on maternal rank, but the process of rank acquisition was also affected by age/size differences between members of different families. Mother-daughter rank reversal was rare, but all old, postreproductive matriarchs were outranked by their adult daughters. Contrary to findings of other studies on macaques, younger sisters seldom outranked older sisters. There was no genealogy with a strict age-inversed hierarchy among adult sisters as described for rhesus and Japanese macaques. Rank reversals between sisters were more frequent in genealogies with old or dead matriarchs, in large clans, and in dyads with an age difference of more than 1 year, indicating that demographic variables influence intra-genealogical dominance relations. It is suggested that close, long-lasting relationships between sisters and mothers and doughters impede rank reversals. Previous evolutionary models of female dominance relations in primates that explain rank relations among sisters as a function of their reproductive value or as a strategy of the mother to maintain her own status are not supported by the data. The results of this and other studies indicate that rank reversal between sisters is not as universal for Old World monkeys, or even macaques, as frequently proposed.

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

Abstract Abstract. 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 females 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.

Reproductive senescence and terminal investment in female Barbary macaques (Macaca sylvanus) at Salem

The reproductive history of 207 female Barbary macaques, living in a large outdoor enclosure in Southwest Germany, was studied during an 11-year period. The results yielded a significant relationship between female age and fecundity, with fertility rates lower than expected among young and old females. Analysis of the reproductive history of individual females revealed a significant decline in fertility from prime age (7–12 years) to mid age (13–19 years), and from mid age to old age (20–25 years). The proportion of long interbirth intervals increased steadily among aging females. Infant survival was not significantly related to maternal age, but offspring of old females showed the highest survivorship. Behavioral observations revealed that old mothers weaned their offspring significantly later than younger mothers, suggesting that prolongation of interbirth intervals is due not only to deteriorating physical condition but also to increased maternal investment, as life history theory predicts. Reproduction ceased during the middle of the third decade of life. Final cessation of estrous cycling invariably occurred 3 or 4 years after the birth of the last offspring, but a postreproductive life span of ≥5 years appears to be common in this population. Available data suggest that reproductive senescence and menopause are more common among nonhuman primates than widely believed and that both traits are part of an adaptive life history strategy.

Adaptive significance of sex ratio adjustment in semifree-ranging Barbary macaques (Macaca sylvanus) at Salem

SummaryNew data on the secondary sex ratio in semi-free-ranging Barbary macaques at Salem confirm the observation that the offspring of high-ranking females in this colony are biased towards sons while the offspring of low-ranking females are biased towards daughters. Analysis of interbirth intervals yielded no consistent differences in the relative costs of rearing male and female offspring for either high- or low-ranking females. Survivorship to adulthood of male and female offspring born to mothers of all rank classes was remarkably high, and there was no indication that juvenile females of low-ranking mothers face any greater risk. Daughters of high- and low-ranking mothers showed no substantial differences in reproductive success, while mating and probably reproductive success of sons seemed to be dependent on maternal rank, at least at the beginning of their reproductive career. The results suggest that variation in sex ratio does increase parental fitness.