Antenna Length in the Hermit Crab Pagurus middendorffii : Sexual Dimorphism and Effect on Two Types of Male–male Competition

Male–male competition is considered a mechanism for sexual selection and the evolution of sexual dimorphism in many animals. There are two types of male–male competition: scramble competition and contest competition. Many studies have focused on contest competition to explain sexual dimorphism of body size and/or weaponry, but it can also result from scramble competition. In this study, we described sexual dimorphism in antenna length of the hermit crab Pagurus middendorffii and tested the effects of antenna length in scramble and contest competition. Although antennae were longer in males than in females, longer antennae provided males no advantage in either competition. These results suggest sexual dimorphism of antenna length in this species is maintained by other ecological factors such as advantage in foraging at the rocky shore