Food Transfer Among Adult Lion Tamarins: Mutualism, Reciprocity or One-Sided Relationships?

Abstract

Tamarins (Callitrichidae) are cooperative breeders. Groups typically contain only two or three breeding individuals and subordinate group members are reproductively suppressed. Nonreproductive individuals, which are usually the offspring of the group's breeding members, delay dispersal while providing care to infant siblings. Callitrichid breeder-infant and helper-infant relationships have been well studied but empirical studies regarding the dynamics of breeder-helper relationships are sparse. I examined food-transfer interactions among parents and natal adults in 7 groups of captive lion tamarins, Leontopithecus spp., to test whether relationships are maintained by mutualism or reciprocity or are to the benefit of one side of a dyad. Individuals that had recently received food from a group member most frequently released food to the previous donor as their next act of transfer. Conversely, food transfer was not dependent on symmetrical relationships within groups over a time frame of several weeks. These results suggest that mutualism plays a role in the maintenance of food-transfer relationships but reciprocity does not. However, there is evidence for a reciprocal relationship between grooming and food transfer in one group. Subadults and adults living in their natal groups transferred proportionally more food to mothers than to oppositely-sexed subadult and adult siblings. Thus, individuals most likely to receive aggression preferentially released food to individuals most likely to inflict injury upon them. Although these results support the coercion hypothesis, they may suggest alternatively that food transfer by helpers to breeding adults is driven by inclusive fitness considerations.