Aggressive behavior and morphology in Scopimera globosa (De Haan, 1835) (Brachyura: Dotillidae)

Abstract

Sexual dimorphism is common in species where one sex fights for access to the other sex, or one sex displays to attract the other sex for mating. We show that in the dotillid crab Scopimera globosa (De Haan, 1835) there is strong sexual dimorphism with males having relatively larger chelae (claws) than females. We also found that males had relatively longer walking legs (pereiopods) than females, a pattern previously shown in a few brachyuran crabs. This species exhibits five distinct aggressive behaviors and males predominantly engage in aggressive interactions. Unlike other brachyuran crabs, males do not grasp each other with their chelae during fights and chela size was not a determinant of winning such interactions. The most escalated fight, the wrestle, involves the raising of the walking legs, and leg length was a strong predictor of fighting success. We suggest that the sexual dimorphism in leg length has evolved in response to the use of the legs in determining fighting success.