Abstract
Intergroup conflict has been suggested as a major force shaping the evolution of social behaviour in animal groups. A long-standing hypothesis is that groups at risk of attack by rivals should become more socially cohesive, to increase resilience or protect against future attack. However, it is usually unclear how cohesive behaviours (such as grooming or social contacts) function in intergroup conflict. We performed an experiment in which we exposed young colonies of the dampwood termite, Zootermopsis angusticollis, to a rival colony while preventing physical combat with a permeable barrier. We measured social contacts, allogrooming and trophallaxis before, during and after exposure. Termites showed elevated rates of social contacts during exposure to a rival compared to the pre-exposure phase, but rates returned to pre-exposure levels after colonies were separated for 9 days. There was evidence of a delayed effect of conflict on worker trophallaxis. We suggest that social contacts during intergroup conflict function as a form of social surveillance, to check individual identity and assess colony resource holding potential. Intergroup conflict may increase social cohesion in both the short and the long term, improving the effectiveness of groups in competition.
Highlights
Classic research on the evolution of cooperation has focused on mechanisms that operate within social groups [1]
Rates of social contacts among colonymates increased during exposure to a rival colony, but returned to pre-exposure levels after colonies had been separated
We suggest that our results reflect the different function of social behaviours in intergroup conflict
Summary
Classic research on the evolution of cooperation has focused on mechanisms (such as kin selection and policing) that operate within social groups [1]. Theoretical models developed to investigate the origins of large-scale human cooperation show that sufficiently intense conflict between groups for resources (intergroup conflict) can select for altruism within groups [5,6]. A hypothesis linked to, but distinct from, these models is that groups exposed to conflict should evolve to respond on a behavioural timescale by becoming more coordinated or cohesive, to increase effectiveness or resilience in group competition [8,9,10] This is a classic idea in sociological and political studies of human conflict (the ‘conflict-cohesion hypothesis’; [11,12]). There is evidence that exposure to rival groups leads to increased ‘social cohesion’, measured by affiliative behaviour such as allogrooming or other social contacts [9,13,14,15]. We tested whether these behavioural responses persist long after colonies had been separated
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