ABSTRACT

Cooperation is everywhere in nature. Cells work together to form bodies, bacteria exchange nutrients with plants, and cooperating individuals form societies. How does cooperation emerge among self-interested units? Answering this question involves studying how cooperation is promoted by individual behaviors such as rewarding, punishing, choosing, or switching partners. These behaviors occur within the larger context of the social network?the partner ?market? defining the supply and demand of particular kinds of partners. To test hypotheses about cooperation, it is useful to study an organism that forms long-term social relationships and that makes complex decisions about which partners to help. The work will use common vampire bats as a model organism because they cooperate by grooming and sharing regurgitated food with related and unrelated long-term partners. Lab experiments with vampire bats will simulate their natural social environments, manipulate their cooperative interactions over time, and test how ?strangers? develop into food-sharing partners that help each other at a cost to themselves. Understanding how vampire bats form social networks can provide general insights into how individual behaviors shape relationships, social structure, cooperation, and the spread of information or disease as vampire bats often feed on the blood of cattle. By attaching tiny wireless sensors on both bats and cattle, the research team will also track the dynamics of the ?bat network? and the ?bat-cow network? in minute-by-minute detail. These large datasets are useful for modelling network-based processes, such as how viruses would spread through a population or transmit across species (e.g. bats to livestock).

Behavioral ecologists disagree about the relative importance of factors like fitness interdependence, partner choice, and partner control for stabilizing cooperative social relationships. The research aims to resolve these longstanding debates by experimentally manipulating the formation of new cooperative relationships over time. The work addresses four levels of increasing complexity: individuals, relationships, networks, and dynamic multi-layer networks. First, how and why does cooperativeness vary among individuals? The team will study of the neuroendocrine causes and consequences of individual variation in allogrooming and food sharing in vampire bats. Second, how do nonkin strangers form new cooperative relationships? The experiments will resolve a decades-long debate about a textbook example of cooperation: reciprocity in vampire bats. Third, how well do different social interaction networks influence each other? The work will link within-roost cooperation to social foraging and will generate rich datasets enabling studies of social structure, social learning, and pathogen transmission. Finally, how does variation in partner availability and quality influence the success of different cooperation enforcement strategies over time? The work will generate new analytical and computational models that will incorporate new forms of social complexity into models of social evolution. Recent work suggests that vampire bats vary in cooperativeness, maintain similar social networks in the lab and field, and form new cooperative relationships by conditionally escalating low-cost grooming investments before investing in higher-cost food sharing (?raising the stakes?).

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