We study the adaptive design of cooperative relationships. How do cooperative animals choose, maintain, and regulate their social relationships?

Theory: How do cooperative traits emerge and persist when non-cooperative traits can better exploit the public good of cooperation? Social evolution theory has largely solved this puzzle with several theoretical frameworks. First, inclusive fitness theory explained why altruism can evolve among kin. Second, concept of reciprocity explained how repeated helping behaviors could be enforced by reward and punishment. Third, biological market theory explained how cooperation can be favored by partner choice and the threat of partner switching, and how asymmetries in cooperation can result from supply and demand. Putting these ideas together lays the foundation for understanding why cooperative traits can evolve and persist through various forms of assortment and enforcement.

The challenge of cooperation in social bonds: The multiple mechanisms that enforce cooperation have been well demonstrated in systems that are easy to manipulate in the lab (like microbes). However, in species where individuals form long-term social bond (like humans), the relative roles of various strategies for stabilizing cooperation remain unclear. This is not surprising because stable social bonds are by definition hard to manipulate. Social bonds are also rather complex because they involve integrating many kinds of experiences over time. Evolutionary models of cooperation typically focus on simple strategies, but strategies that regulate social relationships might respond to many interacting factors. We don’t fully understand to what extent long-term cooperative relationships are enforced or vulnerable to cheating. We don’t really understand how cooperative bonds first develop between strangers. We also don’t know to what extent individuals actively shape their position in their social network.

Our goal is to use experiment and observation to test predictions (from inclusive fitness theory, reciprocity theory, and biological market theory) about the design of cooperative relationships. We study the cooperative relationships of vampire bats because they form long-term bonds and performs natural, frequent, and costly helping behaviors that can be monitored, measured, and manipulated over long time-periods. We try to understand how individual actions leads to changes in relationships and the structure of social networks.

bat on shoulder
me and a vampire bat

Vampires are blood-feeders on a tight energy budget—they can starve to death after just 2-3 nights of unsuccessful hunting, but they can also live for more than two decades. Females regurgitate food to their offspring but also related and unrelated adults. These helping decisions appear to be based on past social experience, because reciprocal donation rates are more important than genetic kinship for predicting food-sharing rates. Nonkin bonds appear to act as form of “social bet-hedging” as relying exclusively on one or a few kin donors is too risky. We can experimentally manipulate cooperative behavior by preventing sharing in specific pairs or by administering intranasal oxytocin or lethargy-inducing LPS.

Ongoing projects

With Rachel Page at Smithsonian Tropical Research Institute, we are looking at how vampire bats that are strangers can eventually develop cooperative relationships.

We are tracking foraging movements and looking for social foraging in free-ranging vampire bats using newly developed encounter-tracking devices that can be placed on both bats and their “prey”.

With Alex Ophir and Angela Freeman at Cornell University, we plan to look at the neuroendocrine basis of cooperation in bats.

With Liz Hobson and Ian Hamilton, we are trying to understand how social networks emerge from the traits of individuals and relationships.

To see examples of our most recent work, see Publications.

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