EVIDENCE THAT SALT WATER MAY NOT BE A BARRIER TO THE DISPERSAL OF ASIAN FRESHWATER CRABS (DECAPODA: BRACHYURA: GECARCINLCIDAE AND POTAMIDAE)

摘要

The true freshwater crabs are a strictly freshwater circumtropical group that is found throughout the inland waters of the continents as well as on numerous islands. We tested competing biogeographic hypotheses for how this distribution pattern arose.Vicariant explanations, based on the belief that true freshwater crabs are unable to tolerate exposure to high salinities, assume that stretches of seawater are significant barriers to dispersal. Dispersalist explanations, based on phylogenetic and fossil evidence, assume that freshwater crabs are capable of at least limited trans-oceanic dispersal. We evaluated the physiological tolerance to sea water of two Thai freshwater crab species held for two weeks in either shallow or deep sea water. Both species survived in full-strength sea water for at least 14 days. Survival rates in high salinities were not affected by body size, gender, or whether crabs were fully or partially submerged. Although freshwater crabs are never found naturally in any aquaticsaltwater ecosystem, physiologically they are euryhaline osmoregulators that do not die immediately in full-strength sea water. These stricdy freshwater decapods can survive in sea water for long enough to disperse across at least short distances between continents and islands. Our findings support dispersalist rather than vicariant explanations for present-day freshwater crab distribution patterns.