SOCIAL BEHAVIOUR AND ITS EVOLUTION IN SCYTODID SPIDERS (ARANEAE: SCYTODIDAE)

Abstract

Sociality is a major innovation in the history of life. Understanding how social behaviour evolved and what maintained it has thus been a focus of evolutionary, behavioural, ecology, genetic and molecular biological research. Despite being a minority, social and subsocial spiders are widely distributed in 10 distinctly unrelated families, including the spitting spider family Scytodidae. With spitting being used in prey capture and in defense against predators, it is easy to think that spiders that spit are unlikely to be social. Yet various forms of sociality have been documented in Scytodidae, hence making it a suitable and useful system for studying the evolution of sociality. In this study, the social behaviour of 19 scytodid species from three different habitat types ¿ caves, ground and vegetation - mostly from Africa and Asia and the evolution of the scytodid sociality were investigated. This was done by using field and laboratory observations and experiments as well as molecular phylogenetic analyses. Four species were found to be subsocial exhibiting traits such as extended maternal care, cooperative prey capture, communal feeding, delayed natal dispersal and a degree of tolerance among brood-mates. This thesis also presents the first phylogenetic analysis of major groups of Scytodidae with focus on the Old World species. Molecular data from 49 species were used to reconstruct the relationships within the Scytodidae and with that of the closely-related families, Sicariidae and Drymusidae. Although support for many nodes is weak, the consensus tree indicates that at least six generic level clades exist within Scytodidae. By mapping social behavioural characters onto the molecular phylogeny of the scytodids, hypotheses about scytodid social evolution were tested. Sociality may have evolved at least four times in Scytodidae.