Data from: Female monkeys use both the carrot and the stick to promote male participation in intergroup fights

Group-level cooperation often poses a social dilemma in which joint action
may be difficult to achieve. Theoretical models and experimental work on
humans show that social incentives, such as punishment of defectors and
rewarding of cooperators, can promote cooperation in groups of unrelated
individuals. Here, we demonstrate that these processes can operate in a
non-human animal species, and be used to effectively promote the
production of a public good. We took advantage of the fact that intergroup
fights in vervet monkeys (Chlorocebus aethiops pygerythrus) are
characterized by episodes of intergroup aggression with pauses in-between.
During pauses, females selectively groomed males that had participated in
the previous aggressive episode, but aggressed male group members that had
not. In subsequent (i.e. future) episodes, males who had received either
aggression or grooming participated above their personal base-line level.
Therefore, female–male aggression and grooming both appear to function as
social incentives that effectively promote male participation in
intergroup fights. Importantly, females stood to gain much from recruiting
males as the probability of winning intergroup fights was dependent on the
number of active participants, relative to the number of fighters in the
opposing group. Furthermore, females appear to maximize the benefits
gained from recruiting males as they primarily used social incentives
where and when high-quality food resources, which are the resources
primarily limiting to female fitness, were at stake.