Allomothering

Allomothering, "alloparental", "infant handling", or non-maternal infant care, is performed by any group member other than the mother or genetic father and thus is distinguished from parental care. It is a widespread phenomenon among mammals and birds. Depending on age-sex composition of groups alloparents, helpers or "handlers" can be non-reproductive males in polyandrous systems, reproductive or non-reproductive adult females, young or older juveniles or older siblings interested in abetting their own genetic material via their siblings (Theory of Inclusive Fitness). Allomothering comprises a wide variety of behaviours including: carrying, provisioning, grooming, touching, nursing (allonursing) and protecting the infants from predators or conspecifics.

Allomothering is particularly common among the Primate order. Vervets, cebus monkeys, squirrel monkeys, and macaques are all known for allomothering performed by females not closely related to the pair. These alloparents help by carrying the infant, providing food, and guarding the infant from predators. Cebus monkey females have been known to regularly nurse (allonurse) infants who are not their own (cf. wet nurse). In these species allonursing is performed by related and unrelated females. Moreover, about 10% of nursing bouts are attributed to allonursing. Allomothering can also be performed by non-reproductive helpers like in the callitrichids (marmosets and tamarins). In the Callitrichids, allomothering care goes beyond many other species and infants are spontaneously provisioned by all group members without a prior begging calls on part of the infants. These species practice facultative cooperative breeding, where a single dominant female reproduces and other group members (fathers, other males and non-reproductive juveniles) provide the majority of care to the infants.

A number of adaptive functions have been proposed to account for the widespread incidences of allomaternal care in mammalian and avian species. Jane Lancaster noted the reproductive benefits for primates as k-strategists in learning to be better mothers, or acquiring mothering skills. Her learning-to-mother hypothesis postulates that primate females with no children of their own participate in allomothering, and evidence from studies by Sarah Hrdy and Lynn Fairbanks shows that females without offspring "tried to allomother more frequently than what you'd expected based on their proportion of the group's population, while parous females tried it much less than expected from their population in the group." The hypothesis is supported by evidence of the success of allomothering as a learning technique. "Lynn Fairbanks studied vervets and found that first-time mothers with high alloparenting experience raised 100% of their first offspring to maturity, but mothers with low experience had less than a 50% survival rate of their first infant." Other hypothesis include "alliance-formation", where subordinate allomothers endeavour to form social alliances with dominant mothers by interacting with their infants. Under kin-selection theory, related allomothers may improve their inclusive fitness if the allomothering behaviour contributes to the survival or faster reproductive rate of the mother. Finally, allomaternal care has been suggested to be a by-product of maternal care. However, this hypothesis would not explain the high levels of care seen by juvenile, subadult or unrelated adult males in many [primate] species.

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