Environmental, sex-specific and genetic determinants of infant social behaviour in a wild primate

Abstract

Affiliative social bonds are linked to fitness components in many social mammals. However, despite their importance, little is known about how the tendency to form social bonds develops in young animals, or if the timing of development is heritable and thus can evolve. Using four decades of longitudinal observational data from a wild baboon population, we assessed the environmental determinants of an important social developmental milestone in baboons—the age at which a young animal first grooms a conspecific—and we assessed how the rates at which offspring groom their mothers develops during the juvenile period. We found that grooming development differs between the sexes: female infants groom at an earlier age and reach equal rates of grooming with their mother earlier than males. We also found that age at first grooming for both sexes is weakly heritable ( h 2 = 0.043, 95% CI: 0.002–0.110). These results show that sex differences in grooming emerge at a young age; that strong, equitable social relationships between mothers and daughters begin very early in life; and that age at first grooming is heritable and therefore can be shaped by natural selection.

An early-life challenge: becoming an older sibling in wild mandrills

“…A common way to gain access to the infant is to initiate a grooming with the mother [89][90][91]. Second, mandrills' sex-specific reactions might reflect life history differences between sexes [72]. Indeed, in such matrilineal society, maintaining and/or reinforcing close social bonds with the mother could be more advantageous for juvenile females than for males, as strong social bonds with close maternal kin in adulthood translate into fitness advantages in female cercopithecines [92,93].…”

“…In these species, immature males typically form weaker bonds with their mother and are less integrated in their matriline, and such sex differences may emerge as early as the first year of life (e.g. [71][72][73]94]). Hence, the birth of a younger sibling may foster the independence of juvenile males, as in free-ranging rhesus macaques [44], while juvenile females may instead react by strengthening their bond with their mother.…”

“…Finally, (P4) juveniles who recently experienced the birth of a younger sibling, and especially those who experienced it at a young age, would display more tantrums and self-directed behaviours than those who did not. For (P2−P4), we explored potential sex-differences in juveniles' reactions to TTS, as sex-differences in mother-offspring bond and social behaviour typically emerge early during development in cercopithecines [71][72][73].…”