We addressed two different aspects of indirect reciprocity in tufted capuchin monkeys (Sapajus spp.) studying two common cooperative behaviours, grooming and food sharing. In an observational study, we tested whether capuchin monkeys were more likely to groom an individual that had just groomed a group mate than an individual that had not groomed anybody. In an experimental study, we tested whether capuchin monkeys were more likely to share their food with a partner when in the presence of a bystander (or of an image of the eyes of a conspecific) than when alone with their partner. In the observational study, we found an increase in the likelihood of receiving grooming after giving grooming, but this effect seemed to depend on social facilitation rather than on indirect reciprocity, as we found a similar effect after receiving (rather than giving) grooming. In the experimental study, the presence of a bystander or of an image of eyes did not affect the amount of food transferred to a group mate. Overall, these results suggest capuchin monkeys do not engage in indirect reciprocity.

中文翻译：

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在簇绒卷尾猴中测试间接互惠的两侧

我们讨论了簇绒卷尾猴（Sapajus spp.）间接互惠的两个不同方面，研究了两种常见的合作行为，梳理毛发和食物分享。在一项观察性研究中，我们测试了卷尾猴是否比没有为任何人梳理过毛发的个体更有可能给刚刚梳理过同伴的个体梳理毛发。在一项实验研究中，我们测试了卷尾猴在有旁观者（或同种眼睛的图像）的情况下是否比单独与伴侣分享食物的可能性更大。在观察性研究中，我们发现在进行梳理后接受梳理的可能性增加，但这种影响似乎取决于社会促进而不是间接互惠，因为我们在接受（而不是给予）修饰后发现了类似的效果。在实验研究中，旁观者或眼睛图像的存在不会影响转移给同伴的食物量。总体而言，这些结果表明卷尾猴不参与间接互惠。