STUDIES ON THE HANDEDNESS OF THE FIDDLER CRAB, UCA LACTEA

¹ Aitsu Marine Biological Station, Kumamoto University, Matsushima-cho, Amakusa-gun, Kumamoto-ken, 861-61, Japan

1. The numbers of right-handed and left-handed males of Uca lactea were nearly equal, and no significant regional or yearly differences from the ratio of 1:1 were found.

2. In the early stages of growth, all the crabs had two small chelipeds, and no morphological differences were found between the sexes. All males with a carapace width greater than 5.3 mm exhibited cheliped asymmetry. Apparently, a male normally loses one of his chelipeds which then regenerates into a small cheliped; the remaining cheliped develops into a giant, and the male attains his cheliped asymmetry.

3. Artificial removal of one cheliped from megalopae and young crabs whose chelipeds were still in the symmetrical condition induced handedness. The large cheliped always developed on the intact side.

4. When males suffered the simultaneous removal of both chelipeds in their megalopa or crab stage before the attainment of asymmetry, they could not develop a giant cheliped but instead kept two small chelipeds permanently. However, no abnormality was recognized in their reproductive function. If a male did not lose a cheliped, two giant chelipeds developed.

5. Once the handedness was established in a male, it could not be reversed by the subsequent removal of one or both chelipeds.