Distribution and hybridization of barred and common grass snakes (Natrix helvetica, N. natrix) in Baden-Württemberg, Southwest Germany. Grass snakes (Natrix helvetica, N. natrix) in Baden-Württemberg

The distribution of the two grass snake species occurring in the German federal state of Baden-Württemberg is described based on genetic data from maternally inherited mitochondrial DNA (mtDNA, up to 1983 bp) and biparentally inherited microsatellite DNA (13 loci). In agreement with previously published morphological evidence, the barred grass snake (Natrix helvetica) occurs in the Upper Rhine Valley and the Black Forest, while the common grass snake (N. natrix, ‘yellow lineage’) is distributed across the remaining more eastern parts of Baden-Württemberg. Cline analyses across two transects running through the region of Karlsruhe and the Black Forest indicate that the hybrid zone is here similarly narrow than the previously characterized stretch near Lake Constance. With respect to nuclear DNA, the Black Forest constitutes no impediment to gene flow in comparison to lowland regions (Karlsruhe, Lake Constance). However, at the eastern slope of the Black Forest, the abrupt replacement of mtDNA of N. helvetica through that of N. natrix indicates that gene flow is mainly male-mediated in this region and that the Black Forest represents a dispersal barrier for female grass snakes.

本研究基于母系遗传线粒体DNA（mtDNA，最长可达1983 bp）与双亲遗传微卫星DNA（13个基因座）的遗传数据，对德国巴登-符腾堡州境内两种草蛇的分布格局进行了系统阐述。与此前已发表的形态学证据一致，环纹草蛇（Natrix helvetica）分布于上莱茵河谷与黑森林地区，而普通草蛇（N. natrix, "黄色谱系"）则分布于巴登-符腾堡州其余偏东部的区域。对横穿卡尔斯鲁厄地区与黑森林的两条样带开展的渐变带分析结果显示，该区域的杂交带宽度与此前在康斯坦茨湖附近探明的杂交带宽度相近。相较于低海拔区域（卡尔斯鲁厄、康斯坦茨湖），黑森林并未对核基因流构成阻碍。但在黑森林东坡，环纹草蛇的mtDNA被普通草蛇的mtDNA快速替代，这表明该区域的基因流主要由雄性介导，且黑森林对雌性草蛇的扩散构成了屏障。