Prosocial behaviours (providing benefits to a recipient with or without cost for the donor) have been found to be highly influenced by sex and by hierarchy. Rodents, in particular, are good model for studying prosocial responses, as they were found to exhibit intentional prosocial behaviours to reward a conspecific, and are very sensitive to reciprocity. In our study, we conducted a Prosocial Choice Test (PCT) in which four capybaras (Hydrochoerus hydrochaeris) living in a social group could choose between three tokens: choosing the prosocial token rewarded simultaneously the subject and a recipient, while choosing the selfish token only rewarded the subject; and choosing the null token provided no reward to anyone. Dominance within each dyad was also studied, both before and during the PCT experiment. Our results showed an influence of hierarchy: subjects were more prosocial towards the recipient when it was a subordinate than when it was a dominant individual. These results could be interpreted as a desire of strengthening a hierarchical rank regarding the subordinate, of punishing aggressive conspecifics (usually the subject’s direct dominant), and of weakening dominant individuals in order to modify the pre-existing hierarchy. Additionally, our results highlighted a direct reciprocity phenomenon, a subject being more likely to be prosocial towards a prosocial recipient. All these findings suggest that prosociality could be well developed in other taxa than Primates and that, in long enough PCT experiments, subtle rules could influence individual prosocial strategies.

亲社会行为（向受助者提供收益或为捐助者提供成本）已受到性别和等级制度的高度影响。啮齿动物尤其是研究亲社会反应的良好模型，因为它们被发现表现出故意的亲社会行为以奖励同种人，并且对互惠性非常敏感。在我们的研究中，我们进行了亲社会选择测试（PCT），其中四个水豚（Hydrochoerus hydrochaeris）生活在一个社会群体中的人可以在以下三个标记之间进行选择：选择亲社会的标记同时奖励对象和接受者，而选择自私的标记仅奖励对象；选择空令牌不会给任何人任何奖励。在PCT实验之前和期间，还研究了每个二元组内的支配性。我们的结果表明了等级制度的影响：当接受者是下属时，受试者比接受者更亲社会。这些结果可以解释为一种愿望，即希望增强下属的等级等级，惩罚侵略性的具体事物（通常是受试者的直接统治者）以及削弱统治者以修改先前存在的等级制度。此外，我们的结果强调了直接的互惠现象，受试者更倾向于亲社会的接受者。所有这些发现表明，在灵长类动物以外的其他类群中，亲社会性也可以得到很好的发展，并且在足够长的PCT实验中，细微的规则可能会影响个体亲社会策略。