Genetic relationships between roost-mates in a fission-fusion society of tree-roosting big brown bats (Eptesicus fuscus)

Kin-based patterns of associations are often observed in group living mammals. Colonies of forest-living big brown bats (Eptesicus fuscus) exhibit fission-fusion roosting behavior and female philopatry. Within a roosting area of forest, adult females are distributed into several subgroups roosting in different trees during the day. At night, adult females leave the roost subgroups to forage and, upon return to the roosting area at dawn, both the individual composition and location of subgroups often change. Individuals exhibit nonrandom roosting associations, and we hypothesized that genetic relationships would influence roosting associations. We determined (1) whether the strength of roosting associations between pairs of bats (based on radiotelemetry) was correlated with relatedness, (2) whether individuals that roosted together in roost subgroups were more related than by chance, and (3) from roost subgroups, the pairs of bats that roosted nonrandomly and whether the proportion of related pairs was higher than expected at random. Relatedness measures were based on microsatellite genotyping and mitochondrial DNA sequences. We found from all analyses that roosting associations were not influenced by relatedness or matrilineal relationships. These results provide clear evidence that, contrary to other mammals, kinship does not mediate roosting associations within forest living big brown bats that exhibit fission-fusion roosting behavior.