Structure, Dynamics, and Neural Codes in a Bat Social Network

Group formation and maintenance are critical for the survival of social organisms. We investigated a colony of highly social, wild Egyptian fruit bats in a laboratory-based cave to comprehensively characterize how their social networks evolve and stabilize over weeks and months. Using state-of-the-art tracking methods and videography, we documented the identities, locations, and social interactions between individual bats. We characterized the structure of social networks based on proximity-based social affiliation and rate of social interactions-and found that the network structure evolved dynamically over a few days after the formation or alteration of the group, and subsequently stabilized. Social dominance relationships initially evolved and then remained stable over several months and were reflected in several aspects of the bats' natural behavior, such as the monopolization of food resources and sleeping arrangements. We also conducted wireless single-unit neural recordings in this freely behaving social colony and investigated hippocampal CA1 neurons. A subset of neurons encoded the relative (egocentric) location of other individuals and tracked the directions and distances to them. These egocentric neurons encoded more strongly high-hierarchy bats. Overall, after an initial dynamic period of group formation, the bats established a highly structured and stable social network, which was reflected in their neural codes.