Dispersal in a colonial spider undergoing rapid range expansion

Colonizing species have high dispersal ability and can establish successfully in new locations. These traits occur in many group-living species, suggesting a positive interaction between group dynamics, demography and dispersal ability. We investigated the interaction between dispersal and behavioral and demographic traits associated with group living in Cyrtophora citricola, a colonial spider undergoing range expansion in Israel. We assessed ecological and demographic characteristics of colonies within the original range and in newly inhabited areas, tested proximate mechanisms of dispersal in semi-natural and laboratory conditions, and employed genetic analyses to assess population genetic structure and infer movement among colonies across the species’ range. Bimonthly surveys of colonies in the Arava valley and the Negev showed that recently colonized sites in the Negev have low persistence. Dispersal tendencies were high among juveniles up to the penultimate instar. Individual dispersal tendency was not consistent across instars and was higher among juveniles whose mothers were in poorer body condition. High food availability, large maternal web, and high web density promoted philopatry of young, indicating negative density-dependent colony growth under conditions of rich prey. We genotyped individuals from different populations across the species range to detect single nucleotide polymorphisms (SNPs). We found low Fst values among western, northern and central Negev populations, suggesting recent common ancestry. The sources are likely the eastern Negev and the Arava; Fst values between the Arava and the north, central and western Negev populations indicate substantial gene flow, especially between the Arava and eastern, central and northern Negev.