LIMB REGENERATION IN FIDDLER CRABS: SPECIES DIFFERENCES AND EFFECTS OF METHYLMERCURY

Open Access
Publisher Website
Google Scholar
Abstract
After autotomy of 7 limbs, Uca pugnax regenerates and molts more rapidly than U. pugilator from the same location. The tropical species U. rapax and U. speciosa also regenerate faster than U. pugilator from the same Florida [USA] location. U. thayeri is the slowest to replace missing limbs, the slowest to harden the carapace after ecdysis, and also requires the greatest injury before autotomy will take place. When kept in groups, U. thyeri stops regeneration after basal growth and will not molt; U. pugilator is only slightly retarded when kept in groups. U. rapax is affected by grouping, showing a lengthened proecdysial phase and terminal plateau, thus delaying molting. Newly regenerated limbs of U. rapax, U. thayeri and U. speciosa are lighter than old limbs and have a conspicuous banding pattern which becomes less obvious during 1 or 2 wk after ecdysis as melanophores move into the interband regions and the limb darkens due to increased dispersion of pigment in the melanophores. In U. pugilator the newly regenerated limbs are very pale in color and remain so for several months, even when animals are maintained on a dark background. When treated with 0.5 mg/l methylmercury, growth was inhibited entirely in U. thayeri. Partial inhibition was seen in U. pugilator, and the least inhibition in U. rapax. Some individuals of U. rapax were able to complete regeneration and molt, but there was no melanin in the regenerated limbs. Inhibition of melanogenesis in regenerated limbs was seen in U. thayeri and to a smaller extent in U. pugilator at 0.1 mg/l methylmercury. The lack of black pigment is probably due to inhibition of melanin synthesis. Some of these crabs developed melanin when kept in clean water after ecdysis. Seasonal differences were noted in all species, but especially in U. thayeri in which regeneration occurred much more rapidly in March-April than in Jan.