“The evolution of cooperation: interacting phenotypes among social partners”

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Mat Edenbrow, Bronwyn H. Bleakley, Safi K. Darden, Charles R. Tyler, Indar W. Ramnarine, and Darren P. Croft

Many pathways to cooperation: Guppies adjust their antipredator behavior to their social partners

Two female guppies predator inspecting in hopscotch formation: that is, they trade off who is risking the most by being closest to the predator.
(Credit: Bronwyn H. Bleakley)

Cooperation among non-related individuals is widespread in both human and non-human animals. However, understanding how cooperation is maintained (i.e. why one individual should pay a cost so another can receive a benefit) has puzzled scientists for generations. One of the key requirements for cooperation to evolve is that individuals have a way to find and associate with social partners that behave similarly to themselves. Few studies, however, have demonstrated how animals do this in the wild. Guppies live in rivers in northern Trinidad that vary widely in composition and number of predators, and wherever there are large predatory fish, guppies cooperate to share the risk to investigate potential threats. A group of researchers from the University of Exeter (UK), Stonehill College (USA), and the University of the West Indies (Trinidad) found that guppies change their antipredator behavior depending on the cooperativeness of their social partners. Such behavioral flexibility provides a mechanism for fish to match social partners’ cooperativeness. In the experiments they paired fish with two different social partners across four interactions and measured how much fish changed their behavior based on both their current social partner and previous partners during past interactions.

One of the field sites in Trinidad.
(Credit: Bronwyn H. Bleakley)

While a fish’s current social partner has the strongest influence on its behavior, longer-lasting effects of interacting with previous partners can be measured in subsequent interactions with other fish. Just how influential social partners are on a fish’s behavior depends on the sex of the fish (males change their behavior more than females) and whether the fish had evolved with predators (fish from low predation populations are more influenced by social partners than fish from high predation populations). The degree to which guppies change their behavior in response to social partners, rather than behaving a particular way, is likely to contribute to whether cooperation evolves in a population. Most importantly, there wasn’t just one route to getting effective cooperation between social partners; different combinations of individuals can lead to successful cooperation. Read the Article