ABSTRACT

Social behavior that involves cooperation in nest building, prey capture, feeding and brood care has arisen independently several times among spiders. In most cases, this form of cooperative behavior has led to the subdivision of the social spider populations into collections of perpetually inbreeding colony lineages that give rise to daughter colonies or become extinct without mixing with one another. The possible consequences of such population structure include intercolony selection leading to femalebiased sex ratios, complex population dynamics leading to frequent colony extinction, and low genetic variability resulting from the isolation of the colony lineages, their small size at foundation, and their high rate of turnover. When trying to explain the phylogenetic distribution of cooperative behavior in spiders, therefore, we need not only to consider the preadaptations that may have facilitated the origin of their sociality (e.g. an irregular web and extended maternal care in the ancestral species), but also the consequences that such highly subdivided population structure might have on the patterns of extinction and speciation of the phylogenetic lineages of social spiders.

INTRODUCTION

When trying to understand the phylogenetic distribution of social behavior in a given group of organisms, we can look backwards in time from the origin of sociality and ask the question: what predisposed those particular lineages to the evolution of social behavior?