We study the adaptive design of cooperative relationships. How do cooperative animals choose, maintain, and regulate their social relationships?
The evolution of cooperation is a central theme in biology. Cooperative traits pose an evolutionary puzzle because non-cooperative traits that exploit the public good of cooperation should be favored by natural selection. Evolutionary theory has largely solved this puzzle with three key ideas. First, inclusive fitness theory shows how kinship can lead to reproductive altruism. Second, reciprocity theory shows that helping others can be evolutionarily stable even among non-kin when helping is conditional on receiving help in return. Third, biological market theory shows that cooperators can ensure mutual benefit by choosing or avoiding partners based on the supply, demand, and relative returns of alternative partners. Together, these theories lay the foundation for understanding how helping others can be a strategic investment in the “snuggle for survival”.
The problem: The mechanisms that enforce cooperation have been demonstrated in systems that are easy to manipulate in the lab (like microbes, plants, ants), but in more complex vertebrate societies (including humans), the mechanisms stabilizing cooperation are more controversial. In part, this is because a gap exists between simple evolutionary models of cooperation and the complex psychology of helping decisions in animals. For animals that live in individualized societies, much cooperation takes place in the context of a stable social bond that seems analogous to a human friendship. We don’t know how these relationships develop, why they develop, or whether they have an adaptive design.
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. What behaviors make cooperation evolutionarily stable? Do cooperative relationships require cooperative investments that can be exploited by others, or does cooperation emerge as the byproduct of purely selfish behavior? What information do animals use to make decisions about whether to cooperate with others? How do individuals weigh different social factors such as kinship vs familiarity, or information from recent vs older social interactions?
Cooperative relationships in vampire bats: We study the cooperative relationships of vampire bats (pictured left on my shoulder) 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.
Vampires are long-lived obligate blood-feeders on a tight energy budget—they can starve to death after just 2-3 nights of unsuccessful hunting. They regurgitate food to offspring but also kin and nonkin adults, and decisions to donate appear to be based on past social experience. Reciprocal donation rates are eight times more important than genetic kinship for predicting food-sharing rates. Nonkin bonds appear to act as form of “social bet-hedging” because relying exclusively on a few kin donors is too risky.
It is possible to experimentally manipulate cooperative behavior by preventing sharing in specific pairs or by administering intranasal oxytocin or lethargy-inducing LPS. With Rachel Page at Smithsonian Tropical Research Institute, we are looking at how vampire bats that are strangers can eventually develop cooperative relationships. With Alex Ophir and Angela Freeman at Cornell University, we plan to look at the neuroendocrine basis of cooperation in bats.
Cognitive ecology: To what extent does natural selection shape how animals learn? Is memory best viewed as a single general cognitive ability or a series of task-specific specialized adaptations such as spatial memory or social memory?
The evolution and ecology of bat social life: How do different bat species interact with each other? How and what do they communicate with social calls? Do they forage together? Do they follow specific individuals? How often do they learn from each other about roosts or food? Do they work together to mob predators, search for food, or keep warm? Do they take actions that are only effective when others’ participate? In collaboration with Simon Ripperger and Frieder Mayer at Museum fur Naturkunde, Berlin, Germany, and Rachel Page at the Smithsonian Tropical Research Institute, we are tracking foraging movements and looking for social foraging in free-ranging vampire bats using newly developed tracking devices placed on both bats and their “prey”. We are also hoping to establish long-term study colonies of bats in the USA.
Example Ongoing Projects: (last updated October, 2017)
- What is the social structure of the frog-eating bat? (with Victoria Flores, Rachel Page)
- How does relatedness explain social structure in bats? (with Jerry Wilkinson)
- Is kin discrimination easier to detect than reciprocity? (with Damien Farine, Gabriele Schino)
- Do female vampire bats have a dominance hierarchy (with Rachel Crisp and Lauren Brent)
- How do new food-sharing bonds develop? Do vampire bats perform reciprocity?(with Rachel Page and Damien Farine)
- How does sickness affect cooperative behavior? (with Sebastian Stockmaier and Rachel Page)
- Is guano a cue to roost-finding in vampire bats?
- Do vampire bat contact calls convey kinship?
- How do social bonds function outside the roost? Do food-sharing partners also share wounds on prey? Do vampire bats forage socially? (with Simon Ripperger, Frieder Mayer, and Rachel Page)
- Do social networks predict microbiome similarity (with K. Yarlagadda, A. Raulo, S. Ripperger)