Data from: Contrasting the distribution of phenotypic and molecular variation in the freshwater snail Biomphalaria pfeifferi, the intermediate host of Schistosoma mansoni

Population differentiation was investigated by confronting phenotypic and molecular variation in the highly selfing freshwater snail Biomphalaria pfeifferi, the intermediate host of Schistosoma mansoni. We sampled seven natural populations separated by a few kilometers, and characterized by different habitat regimes (permanent/temporary) and openness (open/closed). A genetic analysis based on five microsatellite markers confirms that B. pfeifferi is a selfer (s≈0.9) and exhibits limited variation within populations. Most pairwise FST were significant indicating marked population structure, though no isolation by distance was detected. Families from the seven populations were monitored under laboratory conditions over two generations (G1 and G2), allowing to record several life-history traits, including growth, fecundity and survival, over 25 weeks. Marked differences were detected among populations for traits expressed early in the life cycle (up to sexual maturity). Age and size at first reproduction had high heritability values, but such a trend was not found for early reproductive traits. In most populations, G1 snails matured later and at a larger size than G2 individuals. Individuals from permanent habitats matured at a smaller size and were more fecund than those from temporary habitats. The mean phenotypic differentiation over all populations (QST) was lower than the mean genetic differentiation (FST), suggesting stabilizing selection. However, no difference was detected between QST and FST for both habitat regime and habitat openness.

本研究以曼氏血吸虫（Schistosoma mansoni）的中间宿主——高度自交淡水螺菲氏毕氏螺（Biomphalaria pfeifferi）为研究对象，通过对比其表型变异与分子变异探究种群分化模式。我们共采集了7个彼此间隔数公里的自然种群，这些种群分别具有不同的生境类型（永久/临时）与生境开放度（开放/封闭）。基于5个微卫星标记（microsatellite markers）的遗传分析证实，菲氏毕氏螺为自交物种，自交率约为0.9（s≈0.9），且种群内部的遗传变异水平有限。绝大多数成对固定分化指数（FST）均具有统计学显著性，表明种群结构显著，但未检测到距离隔离效应（isolation by distance）。我们对来自7个种群的家系在实验室条件下开展了两代（G1与G2）的饲养监测，历时25周，记录了包括生长、繁殖力与存活率在内的多项生活史性状（life-history traits）。研究发现，在生命早期阶段（直至性成熟），不同种群间的性状存在显著差异。首次繁殖的年龄与体型具有较高的遗传力，但早期繁殖相关性状并未呈现这一趋势。在大多数种群中，G1代螺的性成熟时间晚于G2代个体，且体型更大。来自永久生境的个体，其性成熟时的体型更小，繁殖力却高于临时生境中的个体。所有种群的平均表型分化系数（QST）低于平均遗传分化水平（FST），这提示存在稳定选择（stabilizing selection）作用。然而，无论基于生境类型还是生境开放度，均未检测到QST与FST间存在显著差异。