Quantification of sexual dimorphism in Asellus aquaticus (Crustacea: Isopoda) using outline approaches

A marked sexual dimorphism is often observed in arthropods species in which males perform precopulatory mate guarding. It is generally thought to reflect the influence of sexual selection. Until now, sexual dimorphisms associated with mate guarding have mainly been qualitatively described. However, assessing the effects of sexual selection on sexual dimorphims requires a preliminary quantitative assessment of differences in morphology between sexes. Using Fourier analyses, we tested if morphological dimorphisms could be quantitatively assessed in the isopod Asellus aquaticus. In addition, we checked whether sexual dimorphism in shape was exclusively related to mate guarding through considering characters that are not, a priori, implicated in mating behaviour. To assess the potential role of sexual selection in shaping morphology, we then examined how dimorphic characters could influence males' pairing success. Three characters (pleotelson, paraeopods 4 and 5) differed significantly in shape between males and females. In addition, two characters (pleotelson and paraeopods 4) differed in shape between guarding males and nonguarding males, with the latter being closer in shape to females. This suggests that sexual selection may be partly responsible for the observed morphological divergence between sexes in A. aquaticus. (C) 2002 The Linnean Society of London.