A COMPARATIVE STUDY OF THORACIC AND CHELIPED MUSCLE ASYMMETRY IN MALE FIDDLER CRABS (GENUS:UCA)

Asymmetries in thoracic and leg muscles that move the single huge major cheliped of male fiddler crabs are compared to their contralateral homologues in nine species of Uca. In Minuca (U. longisignalis, U. minax, U. pugnax, and U. rapax) and Boboruca (U. thayeri) species, the major side body muscles are twice as large as the minor muscles, with more muscle fibers. Additionally, the individual sarcomeres are exceptionally long, reaching over 20 µm in length. In contrast, in species of the sub-genus Celuca (U. crenulata, U. panacea, U. pugilator, and U. speciosa), while these muscles may be up to six times larger than their contralateral homologues, with fibers nearly twice as long, the sarcomeres are not so hypertrophied.Major muscles in the chela can be 20 times larger than their contralateral homologues. The largest chela muscles also show exceptionally large sarcomeres among Minuca, but not in Celuca.It is shown that sarcomere lengths are inversely correlated with the speed and duration of the courtship...