PEDOGENETIC SOCIOGENESIS VIA THE SIBLING-ROUTE AND SOME CONSEQUENCES FOR STEGODYPHUS SPIDERS

Cooperative social life originated independently at least 3 times in t he eresid spider genus Stegodyphus. The ultimate and proximate factors for sociogenesis have been analyzed in two African social species, S. dumicola and S. mimosarum. 1. More profitable hunting as the ultimate benefit of sociality can explain group sizes up to 30 individuals. Mo st groups are much larger, reducing average female fecundity. They ben efit mainly from the shelter against predators provided by the compact silk nest as a heritable resource. 2. Sociogenesis is not based on ex tended maternal care but on interattraction and tolerance of juvenile spiders, retained throughout life in females. Their neotenic sociality came to overlap with advanced (pedomorphic) sexual maturity. This evo lutionary pathway towards sociality is called the ''sibling-route''.3. Negative side effects, accumulating with group size, may make sociali ty in Stegodyphus evolutionarily unstable.