Group founding and breeding structure in the subsocial spider Stegodyphus lineatus (Eresidae)

Go-operative behaviour may evolve by enhancing the genetic similarity of gr oup members. Increased group similarity is thought to be the basis for the 'subsocial route' of social evolution in the spider family Eresidae. Two pr ocesses may promote the similarity of individuals within populations or bre eding: groups, namely philopatry in stable environments and founder events in a stochastic environment. We show that both processes led to genetic dif ferentiation within and among populations of the subsocial spider Stegodyph us lineatus. Within populations we distinguished between the genetic struct ure caused by random mating and philopatry in old breeding groups and that caused by newly founded groups consisting of sibs. Such sib-groups suggest that new breeding groups are established primarily by single females. The d ifferent gene coancestries among breeding groups resulted in high variances among single-locus data. The results imply that sex-specific dispersal beh aviour (random male mating-dispersal or female group founding) had differen t impacts on the population structure. This type of population structure, w here within-population philopatry and founder events may lead to differenti al proliferation of breeding groups, is very similar to that presumed for s ocial spiders, and is also one that could provide the conditions for interd emic selection.