Several birds and mammals form affiliative relationships with both kin and nonkin that involve multiple forms of cooperation. When individuals form these long-term cooperative relationships, both the causes and consequences of each individual’s cooperative investments are difficult to study. To understand how individuals form and maintain cooperative relationships, one must ultimately manipulate both associations and interactions to experimentally test for predicted changes in relationship dynamics. In this talk, I will review what we have learned so far from 10 years of experiments with common vampire bats (Desmodus rotundus). These blood-feeding vampire bats regurgitate food to help unfed bats in need, and these costly donations occur reciprocally among both related and unrelated adult females. My work to date suggests that such food sharing has origins in extended maternal care and kin selection, but now provides multiple kinds of direct and indirect fitness benefits through some combination of reciprocity and interdependence. New reciprocal food-sharing relationships form between strangers initially through escalating reciprocal allogrooming, and new allogrooming relationships can be experimentally “seeded” by forcing bats into close spatial proximity. A key concept is that the amount of fitness interdependence in social relationships can change continuously over time, blurring the lines between categorical models of cooperation such as reciprocity and ‘pseudo-reciprocity’.

Gerry Carter
Ohio State University
https://eeob.osu.edu/people/carter.1640