Within-group relatedness is correlated with colony-level social structure and reproductive sharing in a social fish.

In group-living species, the degree of relatedness among group members often governs the extent of reproductive sharing, cooperation, and conflict within a group. Kinship among group members can be determined by the presence and location of neighboring groups, as these provide dispersal or mating opportunities that can dilute kinship among current group members. Here we assessed how within-group relatedness varies with the density and position of neighboring social groups in Neolamprologus pulcher, a colonial and group-living cichlid fish. We used restriction site-associated DNA sequencing (RADseq) methods to generate thousands of polymorphic SNPs. Relative to microsatellite data, RADseq data provided much smaller confidence intervals around relatedness estimates. These data allowed us to document novel patterns of relatedness in relation to colony-level social structure. First, the density of neighboring groups was negatively correlated with relatedness between subordinates and dominant females within a group, but no such patterns were observed between subordinates and dominant males. Second, subordinates at the colony edge were less related to dominant males in their group than subordinates in the colony center, suggesting a shorter breeding tenure for dominant males at the colony edge. Finally, subordinates who were closely related to their same sex dominant were more likely to reproduce, supporting some restraint models of reproductive skew. Collectively, these results demonstrate that within-group relatedness is influenced by the broader social context, and variation between groups in the degree of relatedness between dominants and subordinates can be explained by both patterns of reproductive sharing and the nature of the social landscape