DOI: 10.5061/dryad.dr7sqv9vf
title: Survivorship of geographic Pomacea canaliculata populations in responses to cold acclimation

description: 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.
description: Laboratory cold
 acclimation tests of <i>P. canaliculata</i> 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<b>
 s</b>tatistical analysis<b>:</b> 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 <i>P.
 canaliculata</i> 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 <i>P. canaliculata</i> 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 <i>P.
 canaliculata </i>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<b> </b>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 <i>P</i> value for multiple tests. All statistical
 analyses were performed using SPSS 22.0 (SPSS Inc., Chicago, IL,
 USA).
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