Cooperatively Breeding Cottontop Tamarins (Saguinus oedipus)Do Not Donate Rewards to Their Long-Term MatesKatherine A. Cronin, Kori K. E. Schroeder,and Emily S. RothwellUniversity of Wisconsin–MadisonJoan B. SilkUniversity of California at Los AngelesCharles T. SnowdonUniversity of Wisconsin–MadisonThis study tested the hypothesis that cooperative breeding facilitates the emergence of prosocial behaviorby presenting cottontop tamarins (Saguinus oedipus) with the option to provide food rewards topair-bonded mates. In Experiment 1, tamarins could provide rewards to mates at no additional cost whileobtaining rewards for themselves. Contrary to the hypothesis, tamarins did not demonstrate a preferenceto donate rewards, behaving similar to chimpanzees in previous studies. In Experiment 2, the authorseliminated rewards for the donor for a stricter test of prosocial behavior, while reducing separationdistress and food preoccupation. Again, the authors found no evidence for a donation preference.Furthermore, tamarins were significantly less likely to deliver rewards to mates when the mate displayedinterest in the reward. The results of this study contrast with those recently reported for cooperativelybreeding common marmosets, and indicate that prosocial preferences in a food donation task do notemerge in all cooperative breeders. In previous studies, cottontop tamarins have cooperated andreciprocated to obtain food rewards; the current findings sharpen understanding of the boundaries ofcottontop tamarins’ food-provisioning behavior.Keywords: donation, prosocial behavior, cooperative breeding, cottontop tamarinSupplemental materials: http://dx.doi.org/10.1037/a0015094.suppMany recent attempts have been made to identify evolutionaryorigins of the human tendency to assist others, or to act proso-cially. These searches began reasonably with the closest livingrelative of humans, chimpanzees (Pan troglodytes). However,when chimpanzees have been presented with food donation tasksthat allowed them to provide rewards to conspecifics at little or nocost to themselves, they have not shown a preference to do so(Jensen, Hare, Call, & Tomasello, 2006; Silk et al., 2005; Vonk etal., 2008). The lack of evidence for prosocial behavior in chim-panzees has led to the consideration of two quite different hypoth-eses. One hypothesis is that the human tendency to act in the bestinterest of others is a derived trait that originated after the diver-gence of the human and chimpanzee lineages. A second, broaderhypothesis posits that the tendency to provide benefits to conspe-cifics is not uniquely human but a result of some combination ofsocial or ecological selective pressures.Although chimpanzees are closely related to humans, they aresocially distinct. Chimpanzees are characterized by fission–fusionsocial organization, and communities frequently fragment intosmaller temporary parties (reviewed in Muller & Mitani, 2005).Males remain in their natal communities throughout their lives,whereas females typically disperse when they reach sexual matu-rity. Males are more sociable than females, and social bondsamong males are generally stronger than bonds among females(Muller & Mitani, 2005). Males participate in a wide range ofcooperative activities, including grooming, mate-guarding coali-tions (e.g., Watts, 1998), coalitionary aggression (e.g., Nishida,1983; Riss & Goodall, 1977), hunting (e.g., Boesch, 2002), andboundary patrols (Watts & Mitani, 2001). Although males fre-quently cooperate, they also compete fiercely for high-rankingpositions within their groups, and high-ranking males monopolizeaccess to resources, including receptive females.The competitive social environment of chimpanzees has beenreflected in some laboratory studies of chimpanzee cognition. Hareand Tomasello (2004) reported that chimpanzees were more skill-ful at tasks administered in competitive rather than cooperativecontexts. However, congeneric bonobos (Pan paniscus), which aremore socially tolerant and less aggressive than chimpanzees, weremore successful than chimpanzees at cooperating to obtain amonopolizable food reward (Hare, Melis, Woods, Hastings, &Katherine A. Cronin, Kori K. E. Schroeder, Emily S. Rothwell, andCharles T. Snowdon, Department of Psychology, University of Wisconsin–Madison; Joan B. Silk, Department of Anthropology, University of Cali-fornia, Los Angeles.We thank Andrew Mulder for construction of the apparatus, Bob Beckerfor creation of figures, Daniel Acheson for statistical advice, and themanagement staff of the Callitrichid laboratory. This research was sup-ported by National Institute of Mental Health Grant MH029775, theUniversity of Wisconsin Graduate School Research Committee, a HilldaleProfessorship to Charles T. Snowdon, and a National Science FoundationGraduate Research Fellowship to Katherine A. Cronin.Correspondence concerning this article should be addressed to Kather-ine A. Cronin, Department of Psychology, University of Wisconsin, 1202West Johnson Street, Madison, WI 53706. E-mail: [email protected] of Comparative Psychology © 2009 American Psychological Association2009, Vol. 123, No. 3, 231–241 0735-7036/09/$12.00 DOI: 10.1037/a0015094231Wrangham, 2007). Therefore, although phylogenetic similarity isoften a primary consideration in comparative psychology, socialfactors that might influence the emergence of a trait must beconsidered, and the possibility for convergent evolution betweenmore distantly related species should also be explored.The cooperatively breeding Callithrichidae (marmosets andtamarins) share many social characteristics with humans. Cal-lithrichids, like many humans, exhibit long-lasting heterosexualpair bonds, and offspring are cared for by both parents as well asby older siblings and occasionally unrelated group members.Members of Callithrichid social groups actively share food withand carry infants (Feistner & McGrew, 1989; Snowdon, 1996).Behavioral coordination among group members is well developed,with multiple individuals collaborating and exchanging roles toprovide care for infants, locate food, watch for predators, anddefend their territory. The number of available helpers is positivelycorrelated with offspring survival in both field and laboratoryenvironments (Savage, Giraldo, Soto, & Snowdon, 1996; Snow-don, 1996). In laboratory tasks, unrelated pair-bonded cottontoptamarins (Saguinus oedipus) cooperated to obtain food rewards,and continued to do so even