Behavioural and molecular evidence for selective immigration and group regulation in the social huntsman spider, Delena cancerides

Movement among social groups interacts with the costs and benefits of group-living in complex ways. Unlike most other social spiders, the social huntsman spider, Delena cancerides, appears to enter foreign colonies, discriminates kin from non-kin, and has very limited dispersal options because their bark retreats are rare, making this species an interesting model organism with which to examine the role of inter-colony movement on group-living. We examined movement among field colonies of D. cancerides in three ways: (1) by tracking the dispersal and immigration of marked spiders into foreign colonies; (2) by recording resident spiders' behaviour toward introduced immigrants; and (3) by inferring intra-colony relatedness and immigration patterns through allozyme electrophoresis. Of the marked spiders, only young juveniles moved into neighbouring colonies, whereas subadults and adults did not. Introduced juveniles were tolerated in foreign colonies, whereas introduced adult males and subadults were usually attacked by the resident adult female, unless she had similar sized subadult/adult offspring of her own. Allozyme profiles from unmanipulated field colonies showed that 47% of sampled colonies contained at least one immigrant and that average within colony relatedness was below 0.5. These data align with previous research on the costs and benefits of group-living for D. cancerides, suggesting that spiders actively seek and regulate group membership based on interests of both the immigrant and the colony