Male food defence as a by-product of intersexual cooperation in a non-human primate

Abstract

Males in a number of group-living species fight in intergroup conflicts to defend access to food resources, a seemingly paradoxical behaviour, given that this resource does not usually limit male fitness directly. We investigated the mechanism(s) driving apparent male food defence in wild vervet monkeys (Chlorocebus aethiops pygerythrus) by testing the effect that female resource access, and female audience size and activity had on the response of focal males during simulated intergroup encounters. Males do not appear to defend food to increase the reproductive success of female group members because their response was not influenced by the presence of provisioning boxes that only females could access. Female audience size was also unimportant, suggesting males do not participate in intergroup encounters to advertise their quality to potential mates. However, focal males almost always followed/supported female group members who initiated an approach towards simulated intruders, supporting that male participation largely functions to gain status as a cooperative group member, and that apparent male food defence in this species arises as a by-product of intersexual cooperation. Our study highlights that considering audience composition and activity can reveal the presence of social incentives and illuminate the evolutionary mechanism(s) promoting joint action in intergroup aggression.

Male monkeys use punishment and coercion to de-escalate costly intergroup fights

“…Because male and female vervet monkeys experience very different costs and benefits from participating in intergroup fights [14,44,67], they probably disagree on when to fight versus when to avoid engaging in intergroup aggression. This rspb.royalsocietypublishing.org Proc.…”

“…However, we currently understand little of the strategies that other group-living animals use to resolve the conflicts of interest that arise during n-player cooperative activities. In vervet monkeys, the observed intra-and inter-individual variability in participation indicates that males and females experience very different costs and benefits from participating in intergroup fights [14,44,67]. These differences probably create selective pressure for the evolution of manipulative tactics.…”

Correlates of social role and conflict severity in wild vervet monkey agonistic screams

“…Recordings were made with a Marantz PMD661 (sampling rate of 44.1 kHz, resolution 24 bits) and a Sennheiser MKH416 microphone and stored as wav files. Recordings were based on ad libitum sampling, that is, any call observed during natural conflicts or during conflicts following food provisioning experiments carried out as part of other research, using four different experimental methods (‘box’ experiment: subjects had to retrieve food from a closed container [38], ‘jingle’ experiment: conditioned subjects were rewarded following individualised acoustic cues [39], ‘corn’ experiment: large plastic containers with corn were provided for the entire group to feed on [40, 41], ‘vervetable’ experiment: subjects had to copy a demonstrator’s object manipulations to access a small amount of food [42]). Conflicts occurred in all four experimental conditions.…”

Primates are living links to our past: The contribution of comparative studies with wild vervet monkeys to the field of social cognition

“…A field experiment which simulated between-group encounters via playbacks found that males participated in encounters more often when a female monkey was visibly leading the agonistic encounter. The males' probability of participation did not vary with females' access to food resources, thus suggesting they were not participating to protect females' food sources, but in order to heighten their reputation as a cooperative group member (Arseneau-Robar, Müller, Taucher, van Schaik, & Willems, 2016b).…”