The osmoregulatory abilities of freshwater crabs from Thailand (Potamidae and Parathelphusidae) and biogeographical implications.

摘要

The osmoregulatory ability of four species of true freshwater crabs belonging to the Parathelphusidae (Esanthelphusa dugasti and Sayamia germaini) and the Potamidae (Potamon smithianum and Larnaudia chaiyaphumi), collected from four different localities in Thailand were investigated to test biogeographical hypotheses that depend on oceanic dispersal. Crabs were grouped by species, gender, and age and exposed to a range of salinity regimes from 0 to 30 ppt for up to two weeks in both deep and shallow water. Adult hemolymph osmolality was measured after 5, 9 and 13 days into the experiments, while juvenile hemolymph osmolality was measured at the conclusion of the experiment. Measured hemolymph and external water osmolality were used to determine if crabs were osmoregulating or osmosconforming in salinities ranging from fresh water to sea water. All four species were found to be active osmoregulators, and all survived in salinities up to 30 ppt for at least 5 days, and often much longer. The parathelphusid Esanthelphusa dugasti had the lowest mean hemolymph osmolality (373 mOsm/kg) of all four species, and no significant difference between males and females was found in the survival and osmoregulatory response.; Very small recently hatched potamids seemed to survive best in high salinities compared to adults and juveniles of the same species. Water depth influenced hemolymph osmolality only during the initial days of the experiment.; These results indicate that it is reasonable to believe that true freshwater crabs are capable of surviving for up to two weeks in full strength sea water which would be long enough to survive while crossing short distances between continents and nearby islands.