Sexual dimorphism in northern temperate spiders: Implications for the differential mortality model

We examined sexual size dimorphism in 627 species from 123 genera and 32 families of northern temperate spiders from Great Britain and Ireland with different life histories, using phylogenetically independent contrasts. Web-building and non-web-building, sit-and-walt predators were compared with non-web-building, active hunting spiders. After accounting for phylogenetic effects, we find no evidence of differences in sexual size dimorphism in northern temperate spiders with differing life history/predatory strategies. We discuss the implications of our findings for the generality of the differential mortality hypothesis (Vollrath and Parker, 1992) with respect to spiders with different predatory modes from different habitats and environments. This recent theory proposed that extreme sexual dimorphism in spiders resulted from differential adult mortality as a consequence of different adult life histories. We conclude that this model cannot explain die less extreme dimorphism found in temperate spiders.