MULTIVARIATE MORPHOMETRICS AND SEXUAL DIMORPHISM IN THE ORB-WEB SPIDER METELLINA-SEGMENTATA (CLERCK, 1757) (ARANEAE, METIDAE)

Sexual dimorphism in body size and leg length was investigated in a co mmon orb-weaving spider of Ireland and northern Europe, Metellina segm entata (Clerck, 1757) (Araneae, Metidae). Univariate and multivariate analyses of sexual dimorphism revealed that a greater proportion of be tween sex variation (sexual dimorphism) was attributable to variation in shape than in size. Significant differences were found in the score s for males and females for the first two principal components. PC1 (s hape) accounted for 44.25% of the variation and PC2 (size) 13.01% of t he variation. Although M. segmentata has been attributed with minimal sexual size dimorphism, females were markedly heavier, possibly a refl ection of differential reproductive investment between the sexes, but males had markedly longer legs and broader prosoma. The results are di scussed with regard to existing theories of natural and sexual selecti on, particularly those concerning sexual cannibalism and differential life history traits in males and females. Models that attempt to expla in the evolution of sexual size dimorphism in spiders and of the web b uilders in particular, fail to account for the multivariate nature of dimorphism, especially with respect to shape. (C) 1995 The Linnean Soc iety oi London.