The significance of relatedness and gene flow on population genetic structure in the subsocial spider Eresus cinnaberinus (Araneae: Eresidae)

Interdemic selection, inbreeding and highly structured populations have been invoked to explain the evolution of cooperative social behaviour in the otherwise solitary and cannibalistic spiders. The family Eresidae consists of species ranging from solitary and intermediate subsocial to species exhibiting fully cooperative social behaviour. In this study we, in a hierarchical analysis, investigated relatedness of putative family clusters, inbreeding and population genetic structure of the subsocial spider Eresus cinnaberinus. Five hierarchical levels of investigation ranging from large scale genetic structure (distances of 250 and 50 km level 1 and 2) over microgeographic structure (20 km(2) and 4 km(2), level 3 and 4) to a single hill transect of 200 m (level 5) were performed. The purpose of level 5 was two-fold: (1) to investigate the relatedness of putative family groups, and (2) to evaluate the influence of both family living and sampling design on higher level estimates. Relatedness estimates of putative family groups showed an average relatedness of R=0.26. There was no indication of inbreeding. In contrast to social spiders, genetic variation was abundant, H-e approximate to 0.10. The population genetic structure was intermediate between social and asocial spiders. Genetic variance increased continually across hierarchical levels. Family structured neighbourhoods biased differentiation estimates among level 5 samples (F-ST=0.04) and level 3 and 4 samples (0.07<F-ST<0.18), and apparent inbreeding among level 3 and 4 samples, F-IS>0, was caused by disjunct sampling from separate neighbourhoods. Larger scale samples were highly differentiated 0.12<F-ST<0.26, depending on level and sampling design. Due to a distance effect family living did not influence estimates of the higher level 1. Although the dispersing sex among social spiders and the subsocial E. cinnebarinus differ, females versus males, female behaviour of both sociality classes lead to high genetic variance. (C) 1998 The Linnean Society of London.