Colony nutrition skews reproduction in a social spider

Abstract

Cooperative breeding societies are characterized by alloparental care and unequal distribution of reproduction (skewed reproduction). Competition for resources among group members may determine the reproductive outcome of each individual. In a spider colony, females feed together on prey and therefore may compete over the extraction of specific nutrients required for reproduction. Here we examined the occurrence of skewed reproduction in colonies of the social spider Stegodyphus dumicola (Eresidae) in nature and asked whether competition over specific limiting nutrients is a mechanism leading to unequal distribution of reproduction. We determined the nutritional composition of breeding and nonbreeding females in natural colonies. By supplementing field colonies with prey rich in either proteins or lipids, we examined the effect of these nutrients on female breeding potential. We then determined which nutrients were extracted from prey by breeding and nonbreeding females in a noncompetitive setting. About 40% of the females in natural colonies are potential breeders. Field colonies supplemented with lipid-rich prey had a higher percentage of breeding females than colonies supplemented with protein-rich prey. Furthermore, when feeding alone, nonbreeding females extracted more lipids relative to protein than breeding females. We suggest that lipids are critical for maturation and ovarian development and that competition for lipids determines the skewed reproduction observed in colonies of S. dumicola. © The Author 2008. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved.