Donor payoffs and other-regarding preferences in cotton-top tamarins (Saguinus oedipus)
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Helping others at no cost to oneself is a simple way to demonstrate other-regarding preferences. Yet, primates exhibit mixed results for other-regarding preferences: chimpanzees and tamarins do not show these effects, whereas capuchin monkeys and marmosets preferentially give food to others. One factor of relevance to this no-cost food donation is the payoff to the donor. Though donors always receive the same payoffs regardless of their choice, previous work varies in whether they receive either a food reward or no food reward. Here, I tested cotton-top tamarins in a preferential giving task. Subjects could choose from two tools, one of which delivered food to a partner in an adjacent cage and the other of which delivered food to an empty cage. Thus, subjects could preferentially give or withhold food from a partner. I varied whether subjects received food payoffs, whether a partner was present or absent, and whether the partner was a non-cagemate or the subject’s mate. Results showed that the subjects’ overall motivation to pull either tool declined when they did not receive any food. Additionally, they did not preferentially donate or withhold food, regardless of their own payoff or their relationship with the partner. Thus, cotton-top tamarins do not take advantage of cost-free food giving, either when they might gain in the future (mates) or when they have no opportunity for future interactions (non-cagemates).
KeywordsAltruism Callitrichid Cooperative breeding Inequity Payoff Self-interest
I am grateful for funding from the Ruth L. Kirschstein National Research Service Award (National Institutes of Health). I am particularly thankful to Marc Hauser for help in designing the experiment, for providing the facilities to run the experiment, and for comments on an early version of the manuscript. I appreciate feedback from three anonymous referees. I wish to thank Walt Gardner, Justus Meyer, Nina Strohminger, Heather Trevino, and Abby Wild for assistance in testing the tamarins, and I thank the members the Cognitive Evolution Laboratory at Harvard for valuable discussions about the project. This experiment was conducted in compliance with the Harvard University Animal Care protocols 92-16 and 22-07 and the APA Guidelines for Ethical Conduct in the Care and Use of Animals.
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