Dry vs. Rainy: the seasonal response of freshwater snails in artificial reservoirs of semiarid

Our research aimed to investigate the seasonal distribution of freshwater gastropods, specifically Biomphalaria straminea and Melanoides tuberculata, collected from water supply reservoirs in a semi-arid region of Brazil. Our hypothesis was that the abundances of these species would exhibit seasonal variation influenced by environmental factors such as temperature and water levels throughout the dry and rainy seasons.
During the study, from 2017 to 2020, we collected 5,555 individuals of Biomphalaria straminea and 67,122 individuals of Melanoides tuberculata. Captured using standardised techniques, the data include both species abundance and age classes (juveniles and adults).
Our results revealed a significant seasonal distribution for Biomphalaria straminea, with higher abundances observed during the dry season. In contrast, Melanoides tuberculata showed stable populations throughout the study, with no significant correlation with environmental variables. Temperature and seasonal changes had a greater influence on the abundances of Biomphalaria straminea compared to Melanoides tuberculata.
These findings support our hypotheses regarding the reproductive strategies of these species. Biomphalaria straminea, known for self-fertilisation, exhibited a higher proportion of juveniles concentrated during the dry season. On the other hand, Melanoides tuberculata, which reproduces through parthenogenesis, maintained stable populations regardless of environmental conditions.

本研究旨在调查采集自巴西半干旱地区供水水库的淡水腹足类（freshwater gastropods）的季节分布特征，目标物种为条纹双脐螺（Biomphalaria straminea）与瘤拟黑螺（Melanoides tuberculata）。我们提出的假说为：这两个物种种群的丰度会随干湿季呈现季节性变化，且该变化受温度、水位等环境因子调控。
本研究于2017至2020年间开展，共采集到条纹双脐螺5555只、瘤拟黑螺67122只。所有样本均采用标准化采样技术捕获，数据集包含两个物种的种群丰度与年龄组（幼体与成体）信息。
研究结果显示，条纹双脐螺的分布具有显著季节性，其种群丰度在旱季更高；与之相反，瘤拟黑螺的种群在研究期间始终保持稳定，未与环境变量呈现显著相关性。相较于瘤拟黑螺，温度与季节变化对条纹双脐螺的种群丰度影响更为显著。
本研究结果验证了我们关于这两个物种繁殖策略的假说：以自体受精为主要繁殖方式的条纹双脐螺，其幼体占比在旱季显著升高；而通过孤雌生殖繁衍的瘤拟黑螺，无论环境条件如何变化，种群均保持稳定。