Social cooperation can be exploited and eroded by freeloading, which occurs when some individuals receive help from others at no expense to themselves. Natural selection is expected to favor social organisms that cooperate in ways that prevent such freeloading. Most commonly, altruistic traits become protected from freeloading and self-perpetuating because they help relatives, who also inherit and pass along those same altruistic traits. For cooperation between non-relatives, organisms can potentially prevent freeloading by increasing investment in partnerships that yield returns while decreasing investment in partnerships that are less beneficial. This project uses food sharing in common vampire bats as a model cooperation system to test if and how freeloading is prevented. Female vampire bats will voluntarily regurgitate portions of their own meals to feed hungry roost-mates. This seemingly altruistic behavior occurs among related and nonrelated individuals, is inducible, and is measurable under controlled settings without training. Bats will accept and reject food-sharing partners within a group, which provides a way to test the effects of genetic similarity, familiarity, and reciprocity on cooperative decisions. Through a series of experiments on captive animals this project will address three questions about how vampire bats enforce social cooperation. First, can vampire bats discriminate kin from non-kin using vocalizations? Second, will vampire bats exert social partner choice by preferentially helping partners that reciprocated more than others? Third, in the absence of partner choice, will vampire bats exert social partner control by reducing investments in partners that reciprocate less over time? The project will train undergraduate and graduate students and support several outreach activities, including presentations at academic and public forums. Studying the mechanisms underlying cooperation in nonhuman animals has potential to provide new insight into the origins of human social behavior.
