Behavioural response of workers to repeated intergroup encounters in the harvester ant Messor barbarus
Birch, G; Cant, MA; Thompson, F
Date: 19 June 2019
Journal
Insectes Sociaux
Publisher
Springer Verlag for International Union for the Study of Social Insects (IUSSI)
Publisher DOI
Abstract
The evolution of cooperation in animal societies is often associated with the evolution of hostility
towards members of other groups. It is usually predicted that groups under attack from outsiders
should respond by becoming more cohesive or cooperative. However, the responses of individuals
to real or simulated intergroup ...
The evolution of cooperation in animal societies is often associated with the evolution of hostility
towards members of other groups. It is usually predicted that groups under attack from outsiders
should respond by becoming more cohesive or cooperative. However, the responses of individuals
to real or simulated intergroup encounters vary widely, for reasons that are poorly understood. We
tested how groups of workers of the harvester ant, Messor barbarus, responded to exposure to
members of a different colony versus members of their own colony, and how previous exposure to
an intruder affected the intensity of the within-group response. We found that workers increased in
activity and had more contact with one another immediately following exposure to an ant from a
different colony, but also showed a similar behavioural response to presentations involving an ant
from their own colony. However, exposure to an intruder from a different colony resulted in much
stronger behavioural responses to a second intruder, encountered shortly afterwards. Our results
are consistent with studies of social vertebrates which suggest that exposure to intruders results in
increased social cohesion. Our results also show that exposure to an intruder primes group members
to respond more strongly to future intrusions. Our findings highlight a disconnect between the
assumptions of theoretical models which study the effect of intergroup conflict on social evolution
over many generations, and the short-term behavioural responses that are the usual focus of studies
of intergroup conflict in insects and vertebrates.
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