title: Female monkeys use both the carrot and the stick to promote male participation in intergroup fights.
abstract: 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.
authors.affiliation: Anthropological Institute and Museum, University of Zurich, Zurich, Switzerland thelmajeanmarie.arseneau@uzh.ch.|Inkawu Vervet Project, Mawana Game Reserve, Swart Mfolozi, KwaZulu Natal, South Africa.
authors.forename: T Jean Marie
authors.identifier: 0000-0002-0790-8287
authors.initials: TJ
authors.lastname: Arseneau-Robar
authors.affiliation: Anthropological Institute and Museum, University of Zurich, Zurich, Switzerland.|Inkawu Vervet Project, Mawana Game Reserve, Swart Mfolozi, KwaZulu Natal, South Africa.
authors.forename: Anouk Lisa
authors.initials: AL
authors.lastname: Taucher
authors.affiliation: Anthropological Institute and Museum, University of Zurich, Zurich, Switzerland.|Inkawu Vervet Project, Mawana Game Reserve, Swart Mfolozi, KwaZulu Natal, South Africa.
authors.forename: Eliane
authors.initials: E
authors.lastname: Müller
authors.affiliation: Anthropological Institute and Museum, University of Zurich, Zurich, Switzerland.|Inkawu Vervet Project, Mawana Game Reserve, Swart Mfolozi, KwaZulu Natal, South Africa.
authors.forename: Carel
authors.initials: C
authors.lastname: van Schaik
authors.affiliation: Inkawu Vervet Project, Mawana Game Reserve, Swart Mfolozi, KwaZulu Natal, South Africa.|Department of Biology, University of Neuchâtel, Emile-Argand 11, Neuchâtel, Switzerland.
authors.forename: Redouan
authors.initials: R
authors.lastname: Bshary
authors.affiliation: Anthropological Institute and Museum, University of Zurich, Zurich, Switzerland.|Inkawu Vervet Project, Mawana Game Reserve, Swart Mfolozi, KwaZulu Natal, South Africa.
authors.forename: Erik P
authors.initials: EP
authors.lastname: Willems
mesh_terms: D000374:Aggression; D000818:Animals; D002522:Chlorocebus aethiops / Q000523:psychology*; D003299:Cooperative Behavior; D005260:Female; D006120:Grooming; D008297:Male; D009042:Motivation; D011678:Punishment
keywords: n-player games; public good; punishment; reward; social dilemma; social incentives