Data from: A cryptic invasion within an invasion and widespread introgression in the European water frog complex: consequences of uncontrolled commercial trade and weak international legislation

In western Europe many pond owners introduce amphibians for ornamental purposes. Although indigenous amphibians are legally protected in most European countries, retailers are circumventing national and international legislation by selling exotic non-protected sibling species. We investigated to what extent non-native species of the European water frog complex (genus Pelophylax) have become established in Belgium, using morphological, mitochondrial and nuclear genetic markers. A survey of 87 sampling sites showed the presence of non-native water frogs at 47 locations, mostly Marsh frogs (P. ridibundus). Surprisingly, at least 19% of all these locations also harboured individuals with mitochondrial haplotypes characteristic of Anatolian water frogs (P. cf. bedriagae). Nuclear genotyping indicated widespread hybridisation and introgression between P. ridibundus and P. cf. bedriagae. In addition, water frogs of Turkish origin obtained through a licensed retailer, also contained P. ridibundus and P. cf. bedriagae, with identical haplotypes to the wild Belgian populations. Although P. ridibundus might have invaded Belgium by natural range expansion from neighbouring countries, our results suggest that its invasion was at least partly enhanced by commercial trade, with origins as far as the Middle East. Also the invasion and rapid spread of Anatolian lineages, masked by their high morphological similarity to P. ridibundus, is likely the result of unregulated commercial trade. We expect that Anatolian frogs will further invade the exotic as well as the native range of P. ridibundus and other Pelophylax species elsewhere in western and central Europe, with risks of large-scale hybridisation and introgression.

在西欧，诸多池塘饲养者为观赏目的引入两栖动物。尽管多数欧洲国家已对本土两栖动物实施法律保护，但零售商仍通过售卖外来且未受保护的姊妹物种，规避国内及国际相关立法。本研究借助形态学、线粒体及核遗传标记，探究欧洲侧褶蛙属（Pelophylax）外来物种在比利时的定殖程度。对87个采样点的调查显示，47个位点存在外来水蛙，其中以湖侧褶蛙（P. ridibundus）为主。令人意外的是，其中至少19%的位点还存在携带安纳托利亚水蛙（P. cf. bedriagae）特征线粒体单倍型的个体。核基因分型结果显示，湖侧褶蛙与安纳托利亚水蛙间存在广泛的杂交与基因渐渗现象。此外，通过持牌零售商购得的土耳其起源水蛙样本中，同样检测到湖侧褶蛙与安纳托利亚水蛙，其单倍型与比利时野生种群完全一致。尽管湖侧褶蛙或可通过从邻国自然扩散入侵比利时，但本研究结果显示，其入侵过程至少部分受到商业贸易的推动，其源头甚至可追溯至中东地区。因形态与湖侧褶蛙高度相似而被掩盖的安纳托利亚支系入侵与快速扩散，大概率源于未受监管的商业贸易。我们预计，安纳托利亚水蛙将进一步入侵西欧及中欧其他地区的湖侧褶蛙与其他侧褶蛙属物种的外来与本土分布范围，并带来大规模杂交与基因渐渗的风险。