Data from: Characterising a hybrid zone between a cryptic species pair of freshwater snails

Characterising hybrid zones and their dynamics is a central goal in evolutionary biology, but this is particularly challenging for morphologically cryptic species. The lack of conspicuous divergence between parental types means intermediate hybrid forms often go undetected. We aimed to detect and characterise a suspected hybrid zone between a pair of morphologically cryptic lineages of the freshwater snail, Radix. We sampled Radix from across a contact zone between two mitochondrial lineages (Radix balthica and an undescribed lineage termed MOTU3) and detected admixture between two nuclear genotype clusters, which were significantly but not categorically associated with the mitochondrial lineages. In a model selection approach, we show that the admixture cline is best explained by an interaction between precipitation and temperature gradients over the area, rather than geographic distance. We thus hypothesise that the correlation with climatic gradients suggests environmental selection has played a role in maintaining the hybrid zone. In a 2050 climate change scenario, we furthermore predict an expansion of one of the nuclear clusters and a widening of the hybrid zone as the climate warms and dries.阐明杂交带（hybrid zone）及其动态是进化生物学的核心研究目标之一，但针对形态隐存种（morphologically cryptic species）开展此类研究尤具挑战。由于亲本类群间缺乏显著分化，中间杂交型个体往往难以被侦测识别。本研究旨在探测并阐明淡水椎实螺属（Radix）一对形态隐存谱系间疑似存在的杂交带。我们在两个线粒体谱系（mitochondrial lineage）——即巴氏椎实螺（Radix balthica）与一个被命名为MOTU3的未描述谱系——的接触区域全域采样椎实螺，检测到两个核基因型簇（nuclear genotype cluster）间存在基因混杂（admixture）现象，二者与线粒体谱系虽呈显著关联，但并非完全一一对应。本研究采用模型选择（model selection）方法分析显示，该混杂渐变群（admixture cline）的分布格局最佳解释变量为研究区域内降水与温度梯度的交互作用，而非地理距离。据此我们提出假说：该混杂渐变群与气候梯度的关联性表明，环境选择在该杂交带的维持过程中发挥了关键作用。在2050年气候变化情景（climate change scenario）下，我们进一步预测，随着气候逐渐暖干化，其中一个核基因型簇的分布范围将发生扩张，且杂交带也将随之拓宽。