Survivorship of geographic Pomacea canaliculata populations in responses to cold acclimation
Data files
Feb 26, 2021 version files 1.39 MB
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Experimentdatasets.xls
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Figures_tifformat.rar
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Identification_of_Pomacea_canaliculata.rar
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Identification_of_Pomacea_maculata.rar
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Abstract
1. 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.
2. 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 mid-range, and Huanggang population in northernmost (NM-HG) subtropical zone. For each P. canaliculata population, survival and longevity at six cold acclimation temperature levels (12 °C, 9 °C, 6 °C, 3 °C, 0 °C, and -3 °C ) were quantified, and the effects of location and shell height were examined.
3. 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 sub- tropical was the most sensitive to cold temperatures, particular temperatures below 9 °C. No individuals of the SM-GZ population could survive after stressed for 30d (3℃), 5 d (0℃) and 2 d (-3℃), respectively. For each experimental P. canaliculata population held at 3 °C, 0 °C and -3 °C, individuals with intermediate shell height of 15.0–25.0 mm had significantly higher survivals.
4. 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.
Laboratory cold acclimation tests of P. canaliculata populations were conducted for 60d. To assess responses to different cold acclimation temperatures, survival of populations after a certain exposure time were set for the temperature treatments and used for statistical analysis: T1 (12°C and 9°C, exposed for 30d ), T2 (6°C and 3°C, exposed for 10d) , T3 (0°C and -3°C, exposed for 1d). The derived datasets for all experimental P. canaliculata groups were assessed for normality using a Shapiro-Wilk test before analyses. Box-Cox analysis was employed to meet the requirements of normality when necessary. Two impact factors on survivorship of P. canaliculata under the specific acclimation temperature were considered: geographic location (5 levels) and shell height (3 levels), and results were analyzed with two-way ANOVA followed by the Fisher's Least Significant Difference (at the 0.05 level) for post hoc comparisons. To describe survivorship of P. canaliculata populations as a continuous function of temperature, survival rates (following a 1d exposure) at different temperatures for each population were explored through nonlinear regression analysis. To test whether survival of the snail was related to geographic location, temperature and body size, the Cox proportional hazards regression model (Cox, 1972) with a likelihood ratio test was employed, using replicates as random effect. For any given combination of population- temperature-size trial, the differences in the proportion of snail surviving between treatment boxes and their corresponding controls (i.e, the SM-GZ population, corresponding to the fifth sampling location; at temperature of 12°C, corresponding to the highest temperature acclimation regime, and snail in H1 group, corresponding to small juveniles with shell height of 7.5–12.5 mm) were further compared. In these cases, Bonferroni corrections were used to adjust the P value for multiple tests. All statistical analyses were performed using SPSS 22.0 (SPSS Inc., Chicago, IL, USA).
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