Survivorship of geographic Pomacea canaliculata populations in responses to cold acclimation

Pomacea canaliculata, a freshwater snail from South America, has rapidly established natural populations from south to north subtropical region in China, since its original introductions in the 1980s. Low temperature in winter is a limiting factor in the geographic expansion and successfully establishment for apple snail populations. There have been some studies on population level of low temperature tolerance for P. canaliculata, yet little is quantified about its life-history traits in responses to cold temperatures. Whether these responses vary with the acclimation location is also unclear. We investigated the survivorship and longevity of P. canaliculata in responses to cold temperatures and examine whether these responses vary with the location and snail size. We hypothesized that survival of the snails depends on their shell height and the level of low temperature, and P. canaliculata population from the mid-subtropical zone may exhibit the highest viability over the cold thermal range. We sampled P. canaliculata populations from five latitude and longitude ranges of subtropical China: Guangzhou population in southernmost (SM-GZ), three populations of Yingtan (MR-YT), Ningbo (MR-NB), Ya'an (MR-YA) in midrange, and Huanggang population in northernmost (NM-HG) subtropical zone. For each P. canaliculata population, survival and longevity at six cold acclimation temperature levels (12, 9, 6, 3, 0, and -3 degrees C) were quantified, and the effects of location and shell height were examined. The MR-YA population from mid-subtropical zone of China exhibited the highest survival rate and prolonged survival time regardless of the temperature acclimation treatments, whereas the SM-GZ population from southern subtropical was the most sensitive to cold temperatures, particular temperatures below 9 degrees C. No individuals of the SM-GZ population could survive after stressed for 30 days (3 degrees C), 5 days (0 degrees C) and 2 days (-3 degrees C), respectively. For each experimental P. canaliculata population held at 3, 0, and -3 degrees C, individuals with intermediate shell height of 15.0-25.0 mm had significantly higher survivals. The results highlight a request of a more thorough investigation on acclimation responses in each of the life table demographic parameters for P. canaliculata, and pose the question of whether natural selection or some genetic changes may have facilitated adaptation in invasive locations.