Sexual size dimorphism: Patterns and processes

Odonates provide excellent model organisms for testing functional explanations of sexual size dimorphism (SSD) because of their wide variety of habitats, morphology, development, feeding behaviour, and mating strategies. This chapter discusses three major functional hypotheses of SSD and uses data on 133 odonate species to describe their patterns of SSD. It shows that SSD centres around monomorphism in dragonflies, whereas SSD is mostly male-biased in damselflies. Interestingly, phylogenetic comparative analyses suggest that damselflies - but not dragonflies - exhibit allometry consistent with Rensch's rule. Sexual selection acts mainly on males, whereas fecundity selection appears to influence female body size. Further tests, however, are essential, in particular of fecundity selection and the differential niche-utilization.