Food sharing in golden lion tamarins (Leontopithecus rosalia): Provisioning of young, maintenance of social bonds, and resource constraints

Food sharing is an integral part of the cooperative breeding system of marmosets and tamarins. Food is transferred between all group members, but immatures are by far the most frequent recipients. Food sharing behavior was studied in zoo-living groups of lion tamarins (Leontopithecus spp.). Two alternate hypotheses regarding the benefits of provisioning to recipient young were experimentally tested. One hypothesis posits that food transfer may function to supplement infant nutrition, while the other suggests that young learn food preferences through exposure to food items obtained from older group members. Adults transferred to immatures foods that were novel to immatures more frequently than foods that were familiar to immatures. Results are compatible with the hypothesis that food transfer to older immatures functions to inform immatures about diet, in contrast to studies of younger immatures which support the alternate hypothesis. A correlational approach was used to test whether food sharing and allogrooming relationships among adults and subadults are maintained by mutualism, reciprocity or coercion. Neither food sharing nor grooming was dependent on symmetrical relationships, as expected if the behaviors were maintained by mutualism or reciprocity. Moreover, natal subadults and adults preferentially shared food with individuals most likely to inflict injury upon them. In other words, nonreproductive group members may use food sharing to gain tolerance from dominant group members. Results, therefore, support the coercion hypothesis. Finally, an experimental investigation of the effects of variation in resource qualities on food sharing and aggressive behaviors revealed that adult study subjects facultatively adjusted the amount of food shared and aggression given as a function of change in cost of obtaining the contested food item. Foraging task difficulty and search duration influenced food sharing decisions, while food abundance did not. In sum, food transfer behavior in lion tamarins plays important roles both in the development of young and in the maintenance of adult social bonds. By providing food to immatures, older group members may augment juvenile tamarin dietary knowledge. This critical infant caregiving behavior also appears to have been modified for use among adults to stabilize their extraordinarily cooperative social system.