Asymmetry of Leg Size and Differential Leg Usage in the Sand Fiddler Crab, Uca Pugilator

Abstract

Abstract In fiddler crabs, males develop profound left-right asymmetry as a large claw grows opposite a small feeding appendage. Females are symmetrical, with paired small feeding appendages. The claw, used in signaling and contests, may favor adaptive responses in walking legs. This study of sand fiddler crabs, Uca pugilator, investigates differences in leg size and proportion: 1) between major (with the claw) and minor (without the claw) sides, using 404 males from which a pair of legs was removed, and 2) between males and females, using 1085 adults from which a single leg was removed. Among males, only the first walking leg was longer on the major side. This was due to the much greater length of the merus, a proximal long segment that is held parallel to the ground. The merus was longer on the major side in all walking legs. This may permit the claw to be extended away from the body without loss of balance when males either engage in contests over breeding burrows or wave the claw to attract females to...