Survivorship of geographic Pomacea canaliculata populations in responses to cold acclimation

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.

1. 福寿螺（Pomacea canaliculata）是源自南美洲的淡水螺类，自20世纪80年代首次引入中国以来，已在我国亚热带区域从南向北快速建立自然种群。冬季低温是制约该福寿螺种群地理扩张与成功定殖的关键限制因子。目前已有部分针对福寿螺种群水平低温耐受性的研究，但针对其响应低温的生活史特征的量化研究仍较为匮乏，且这些响应是否因驯化地点而异也尚不明确。本研究针对福寿螺响应低温的存活率与寿命展开调查，同时检验这些响应是否随采样地点及螺体规格发生变化。我们提出如下科学假说：福寿螺的存活率取决于其壳高与低温强度，且源自亚热带中部区域的福寿螺种群在整个低温温度范围内的生存能力最强。
2. 本研究从我国亚热带区域的五个经纬度梯度采集了福寿螺种群：最南端的广州种群（SM-GZ）、位于亚热带中部的鹰潭种群（MR-YT）、宁波种群（MR-NB）与雅安种群（MR-YA），以及最北端的黄冈种群（NM-HG）。针对每个福寿螺种群，我们量化了其在6个低温驯化温度梯度（12℃、9℃、6℃、3℃、0℃与-3℃）下的存活率与寿命，并检验了采样地点与壳高的影响效应。
3. 源自我国亚热带中部的MR-YA种群，无论接受何种低温驯化处理，均表现出最高的存活率与最长的存活时长；而来自南亚热带的SM-GZ种群对低温最为敏感，尤其在9℃以下的低温环境中。SM-GZ种群的个体在3℃胁迫30天、0℃胁迫5天以及-3℃胁迫2天后，均无个体存活。对于在3℃、0℃与-3℃环境下的实验福寿螺种群，壳高处于15.0–25.0 mm区间的中等规格个体存活率显著更高。
4. 本研究结果提示，需针对福寿螺各生命表种群统计参数的驯化响应开展更系统的深入研究，同时提出了一个科学问题：自然选择或特定遗传改变是否推动了其在入侵区域的适应性演化。