We study the adaptive behaviors that underlie cooperative social relationships. Do individual animals choose more cooperative social partners? How do they enforce returns on cooperative investments? What are the consequences for these decisions on societies as a whole?

The evolution of cooperative traits was a longstanding puzzle that has been essentially solved by more than four decades of field studies and experiments assessing predictions from multiple theories of social evolution including: inclusive fitness theory, interacting phenotypes, multilevel selection, reciprocity, and biological markets. Each theory emphasizes different factors that shape the evolution of social behavior (e.g. relatedness, scale of competition, assortment by phenotype, repeated interactions, and partner choice). In the real world, these factors often work together and interact. That is, cooperation is evolutionarily stable for multiple reasons.

The factors stabilizing enforce cooperation are best understood in systems that are easy to manipulate in the lab, like microbes. By contrast, in species where individuals form complex long-term social bonds (like human and other primates), the relative roles of various strategies for stabilizing cooperation remain unclear. Unlike mutualistic relationships based on exchange (e.g. when plants and fungi trade carbon for phosphorus), stable social bonds involve many different kinds of interactions and are, almost by definition, hard to manipulate. The quality and quantity of these social bonds often impact the health, survival, and reproduction of individuals, but we don’t fully understand the social strategies that make these relationships work. To what extent are long-term cooperative relationships actively enforced by partner choice or partner control? How do cooperative relationships first develop between strangers? To what extent do individuals actively shape their social network ties?

Our goal is to use experiment and observation to test predictions (from inclusive fitness theory, reciprocity theory, and biological market theory) about the forces or strategies that create and maintain 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 (in 2013)

Vampires are blood-feeders on a tight energy budget—they can starve to death after just 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.

Here’s the most recent talk I gave summarizing much of our work

Five recent papers (link to all publications and PDFs):

  1. Carter et al. 2020. Development of new food-sharing relationships in vampire batsCurrent Biology.
  2. Stockmaier et al. 2020. Sickness effects on social interactions depend on the type of behaviour and relationshipJournal of Animal Ecology
  3. Ripperger et al. 2020. Thinking small: next-generation sensor networks close the size gap in vertebrate biologgingPLoS Biology.
  4. Carter G et al. 2019. Challenges with assessing the roles of nepotism and reciprocity in cooperation networksAnimal Behavior.
  5. Ripperger SP*, Carter GG* (*equal contributions) et al. 2019 Vampire bats that cooperate in the lab maintain their social networks in the wild. Current Biology.

Ongoing projects

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

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