Female parity, maternal kinship, infant age and sex influence natal attraction and infant handling in a wild colobine (Colobus vellerosus)

Abstract

Primate females often inspect, touch and groom others' infants (natal attraction) and they may hold and carry these infants in a manner resembling maternal care (infant handling). While natal attraction and infant handling occur in most wild colobines, little is known about the factors influencing the expression of these behaviors. We examined the effects of female parity, kinship, and dominance rank, as well as infant age and sex in wild Colobus vellerosus at Boabeng-Fiema Monkey Sanctuary, Ghana. We collected data via focal sampling of females in 2008 and 2009 (N = 61) and of infants in 2010 (N = 12). Accounting for the individuals who interacted with our focal subjects, this study includes 74 females and 66 infants in 8 groups. We recorded female agonistic interactions ad libitum to determine dominance ranks. We used partial pedigree information and genotypes at 17 short tandem repeat loci to determine kinship. We knew female parity, infant age and sex from demographic records. Nulliparous females showed more natal attraction and infant handling than parous females, which may suggest that interactions with infants are more adaptive for nulliparous females because they learn mothering skills through these behaviors. Compared to non-kin, maternal kin were more likely to handle infants. Maternal kin may be permitted greater access to infants because mothers are most familiar with them. Handlers may incur inclusive fitness benefits from infant handling. Dominance rank did not affect female interactions with infants. The youngest infants received the most natal attraction and infant handling, and male infants were handled more than female infants. The potential benefits of learning to mother and inclusive fitness, in combination with the relatively low costs of natal attraction and infant handling, may explain the high rates of these behaviors in many colobines.

Alloparenting is associated with reduced maternal lactation effort and faster weaning in wild chimpanzees

“…This emphasizes the importance of separating natal attraction and infant handling when studying the potential fitness impacts of alloparenting, as they probably present different costs and benefits [76,79]. Excluding ‘kidnapping’, which has not been seen at Ngogo, infant handling is a good indication of which individuals mothers permit to hold their infants [8,94].…”

“…High mean relatedness between chimpanzee females at Ngogo [37] may facilitate alloparenting. Indeed, preliminary analyses indicate that maternal kin dyads showed more natal attraction and infant handling than non-kin and unknown-kin dyads [106]. However, not all females who have remained at Ngogo as adults continue to associate with their mothers at high rates [110], and how much alloparenting is directed towards younger siblings remains an open question.…”

“…We did not include time out of view when calculating the total number of focal hours in our analyses. To maximize independence between samples, those on a given infant were separated by at least 30 min unless the infant changed its behavioural state; for instance, if an infant changed from ‘resting’ to ‘feeding’ before the 30 min had passed, we could start a new focal sample on that infant [76]. Otherwise, at the end of a sample, I.B.…”

“…Mothers were either primiparous (first-time mothers) or multiparous (have had more than one infant). Second, we included the sex of infants as a covariate because this can affect the lactation performance of mothers [41,42] and the amount of alloparenting infants receive [76], and because sex differences in rates of weaning and development are known to occur in primates, including chimpanzees [52,87]. The sex of study infants was determined from observations of their genitalia.…”

“…Individuals other than mothers can show interest in infants through touching, peering, playing or grooming (natal attraction), or they may hold or carry infants (infant handling) [76–79]. Natal attraction in primates often occurs when infants are in body contact with their mothers, which means that infants may continue to have maternal nursing access, and reveals the individuals most interested in interacting with infants.…”