Body condition and food shapes group dispersal but not solitary dispersal in a social spider

Abstract

Dispersal is important for the exploitation of new habitat and for outbreeding. A precondition for sociality in spiders is reduced dispersal propensity leading to largely inbred societies. Despite this, social spiders have been observed to disperse from natal colonies and form new or satellite colonies. Proximate factors shaping dispersal, inter-individual variation in dispersal propensities, and any advantages accrued from dispersal remain obscure. In the social spider Stegodyphus sarasinorum, we distinguish 2 types of dispersal: 1) group dispersal in which groups of sub-adult spiders move to form adjacent satellite colonies that are connected to the natal retreat by a shared capture web and 2) solitary dispersal, where a single mated female disperses from the natal colony and can potentially establish a new independent colony. Using experimental colonies that varied in size and subjected to long-term differential food treatment, we show that individuals that participate in group dispersal had lower body condition than natal females. Well-fed colonies had more group dispersers compared to less-fed colonies. Body condition, food availability, and colony size did not influence solitary dispersal. Interestingly, solitary dispersers suffered heavy mortality (~75%) likely due to predation; however, survivors gained better body condition and higher fat reserves post-dispersal compared to natal females. We did not detect greater fitness (measured as clutch size and mean egg weight) in solitary dispersers. Finally, by following group dispersers and natal females, we found that both were equally likely to become solitary dispersers suggesting that solitary and group dispersal are 2 different dispersal strategies.