Fine-scale genetic structure in co-operatively breeding Palmchats (Dulus dominicus) suggests mixed kinship in compound nests

Fine-scale genetic structure in animal populations can create opportunities for both kin-directed co-operation and kin competition. Knowledge of kinship is therefore key to understanding the selective pressures shaping sociality as well as the effects of social behaviour on local genetic structure. Here we investigate patterns of relatedness in compound nests of Palmchats Dulus dominicus, a co-operatively breeding bird endemic to Hispaniola. Compound nests are large stick structures that contain separate nesting chambers attended by different breeding pairs and putative family groups (breeding pairs and non-breeding helpers); nests are occupied and maintained year-round. We captured and genetically sampled 102 Palmchats from 10 compound nests (range = 6–17 birds captured per nest) and genotyped them with 779 single-nucleotide polymorphisms (SNPs). Both relatives and non-relatives were associated with compound nests: the majority of dyads were unrelated, but some dyads were consistent with first- or second-order kin relationships. Average genetic relatedness, although low, was higher within nests than between nests for all types of dyads (female–female, female–male and male–male). Patterns of spatial autocorrelation revealed no association between relatedness and distance between compound nests for either males or females. The population exhibited weak (though significant) overall genetic structuring as measured by F_ST, indicating that low levels of genetic variance within the population existed between compound nesting groups. However, we detected no significant patterns of isolation-by-distance nor significant differences between the sexes. Groups of Palmchats using compound nests appear to be composed of kin and non-kin, suggesting that social nesting involves both direct and indirect fitness benefits.