TOLERANCE TO LOW TEMPERATURE AND DESICCATION IN TWO INVASIVE APPLE SNAILS, POMACEA CANALICULATA AND P. MACULATA (CAENOGASTROPODA: AMPULLARIIDAE), COLLECTED IN THEIR ORIGINAL DISTRIBUTION AREA (NORTHERN AND CENTRAL ARGENTINA)

We collected the invasive apple snails, Pomacea canaliculata and P. maculata (formerly, P. insularum), in their native endemic regions of Argentina and investigated tolerances to cold and desiccation, in order to ascertain any difference between the species and to compare these traits with those reported for apple snails in invaded areas of Asia. All of the four studied populations of P. canaliculata and P. maculata showed enhanced cold tolerance after cold acclimation, as reported for P. canaliculata in invaded areas. Two populations of P. canaliculata and one population of P. maculata that had been suggested to be hybrid based on nuclear gene structures were found to have a tolerance to cold temperature approximately similar to that reported for P. canaliculata in Japan. However, the remaining population of P. maculata, which had been suggested to be the pure line, was less tolerant to cold. The same population of P. maculata, collected in a permanent lake, was much less tolerant to desiccation than the other three Pomacea populations, which were collected from ephemeral ponds. Two probable hybrid populations of P. canaliculata and P. maculata showed desiccation tolerance that was intermediate between the pure lines of both species. On the basis of these results, in addition to probable hybridization between the two species, we suggest that P. canaliculata snails might have a better ability to colonize Asian paddy ecosystems than P. maculata.