Ecophenotypic physiology: osmoregulation by fiddler crabs (Uca spp.) from the northern Caribbean in relation to ecological distribution

Nine species of Uca were collected across the northern Caribbean from 50 locations ranging in habitat osmolality from 18 to 2760 mmol kg-1 (mosmol). The osmoregulating ability of each species was assessed in solutions ranging from 30 to 3550 mosmol. Survivorship, lower and upper median lethal concentration and haemolymph isosmotic concentration ([ISO]) were estimated for each. A lower lethal concentration could not be calculated for some due to survival in low osmolality. By subgenus, average [ISO] for four species from the subgenus Minuca ranged from 587 to 768 mosmol and three species from the subgenus Leptuca from 805 to 881 mosmol. For species from the subgenus Boboruca and the subgenus Uca the [ISO] was 805 and 930 mosmol, respectively. These values reflect the habitat preference of each species in a subgenus. This study broadens our understanding of ecological physiology in Caribbean Uca and demonstrates intra- and inter-specific differences among tropical fiddler crabs.