Sexual size and shape dimorphism in two species of newts, Triturus cristatus and T-vulgaris (Caudata : Salamandridae)

Morphometric data from Fennoscandian populations of the crested newt Tritur us cristatus and the smooth newt Triturus vulgaris were analysed for the pr esence of sexual size and shape dimorphism. The data sets included nine bod y-related and nine head-related measurements and were examined with univari ate, bivariate and multivariate methods. Sexual dimorphism was demonstrated in both species. The separation of specimens was highly related to sex. Al though the expression of sexual dimorphism differed between the two species , some patterns were shared. These are discussed in terms of evolution of i ntersexual dimorphism according to models of ecology, fecundity and sexual selection. In multivariate analyses, sexual dimorphism was restricted to bo dy-related variables such as standard length and distance of extremities (w ith high values for females), contrasting against cloaca and limb-related c haracters (with high values for males). In both species, the 'distance of e xtremities' measure (i.e. trunk length) was one of the strongest sexually d imorphic traits. No evidence of sexual dimorphism in head morphology was fo und. The results are interpreted as primarily concordant with theories on f ecundity selection. For example, it has been suggested that females with la rger trunk volumes increase their reproductive capacity. The fact that male s had longer extremities, in relation to other characters measured, could b e attributed to sexual selection. Long limbs in male newts may be beneficia l for courtship performance. Since head-related characters did not show any patterns of sexual dimorphism, no evidence was found to suggest that male and female crested and smooth newts have adapted to different feeding strat egies.