Population genomics of Sociable Weavers Philetairus socius reveals considerable admixture among colonies

Abstract

The evolution of sociality often leads to genetic structuring among groups and alters the evolutionary forces that the groups experience. Describing the genetic structuring of social species is, therefore, necessary to understand the selective forces that act on a species. While recent work has used genomic methods to investigate population structure in eusocial insects, relatively little genomic work has examined population structure in the largest non-human mammal and avian clades. We delimited population genetic structuring in Sociable Weavers (Philetairus socius), a passerine that lives in large, stable, perennial colonies, using the genotyping-by-sequencing approach to generate a dataset of several thousand SNPs. We used the SNPs to estimate genetic structuring within and among eight nests. While we document relatively low levels of genetic structuring among nests, the structuring was not explained by distance between nests. We also found significantly higher structuring among male Sociable Weavers compared to female weavers, suggesting that female Sociable Weavers are more prone to dispersal in this species. Not all nests represent distinct genetic groups according to Bayesian clustering analysis, which is unsurprising given the low differentiation among nests, especially compared to other social species. In almost all colonies there was less heterozygosity than expected, possibly due to reproductive skew within each colony.