Evolution of social organization: phylogenetic analyses of ecology and sexual selection in weavers

Crook published a landmark study on the social organization of weavers (or weaverbirds, family Ploceidae) that contributed to the emergence of sociobiology, behavioral ecology, and phylogenetic comparative methods. By comparing ecology, spatial distribution, and mating systems, Crook suggested that the spatial distribution of food resources and breeding habitats influence weaver aggregation, both during the breeding season (colonial vs solitary breeding) and non-breeding season (flocking vs solitary foraging), and the food resources distribution and breeding aggregation of individuals in turn impact mating systems and sexual selection. Although Crook's study stimulated much follow-up research, his conclusions have not been scrutinized using phylogenetically controlled analyses. We revisited Crook's hypotheses using modern phylogenetic comparative methods and an extended dataset of 107 weaver species. We showed that both diet and habitat type are associated with spatial distribution and the latter predicts mating system, consistent with Crook's propositions. The best supported phylogenetic path model (PPA) also supported Crook's arguments, and uncovered a direct relationship between non-breeding distribution and mating system. Taken together, our phylogenetically corrected analyses confirm Crook's conjectures on the roles of ecology in social organizations of weavers; however, our analyses also uncovered an association between non-breeding distributions and mating systems, which was not envisaged by Crook.Funding provided by: British Ornithologists' UnionCrossref Funder Registry ID: http://dx.doi.org/10.13039/100008023Award Number: 2019 Career Development Bursar