Everts Teun, Deflem Io, Van Driessche Charlotte, Neyrinck Sabrina, Ruttink Tom, Jacquemyn Hans, Brys Rein
Research Institute for Nature and Forest, Genetic Diversity, Geraardsbergen, Belgium.
KU Leuven, Department of Biology, Plant Conservation and Population Biology, Heverlee, Belgium.
Heredity (Edinb). 2025 May 16. doi: 10.1038/s41437-025-00766-w.
Rapid range expansions are characteristic for non-native invasive species when introduced outside their native range. Understanding the dynamics and mechanisms of expanding non-native invasive species is key for regional management. While population genetics and long-term occurrence records are often used in this context, each provides only partial insights, highlighting the need for a combined approach. We demonstrate this synergy using the American bullfrog (Lithobates catesbeianus) invasion in the Grote Nete river valley (Belgium) as a case study. It is commonly believed that this invasion constitutes a single metapopulation established by one primary introduction followed by downstream dispersal. However, recent evidence suggests a more complex scenario, involving introduction at multiple locations and bidirectional dispersal. To differentiate between both scenarios, we analysed nearly three decades of occurrence records and 8592 single nucleotide polymorphisms across 372 individuals from 31 localities, and determined the number of source locations, the range expansion rate, the population genetic structure, and the magnitude and direction of gene flow. We found that invasive spread originated from up to six source locations followed by bidirectional dispersal and downstream long-distance dispersal (LDD) events. Our results suggest that at least two source locations were founded by primary introductions, two from LDD events, while the remaining resulted from secondary introductions. A canal crossing the river was identified as a dispersal barrier, leading to different invasion dynamics on both sides. Our study shows how asynchronous introductions at multiple locations, dispersal barriers, and environmental heterogeneity can lead to distinct spread dynamics within a seemingly continuous and interconnected metapopulation.
快速的范围扩张是外来入侵物种在其原生范围之外被引入时的特征。了解外来入侵物种扩张的动态和机制是区域管理的关键。虽然种群遗传学和长期出现记录在此背景下经常被使用，但每种方法都只能提供部分见解，这凸显了采用综合方法的必要性。我们以美国牛蛙（Lithobates catesbeianus）在比利时格罗特内特河谷的入侵为例，展示这种协同作用。人们普遍认为，这次入侵构成了一个由一次主要引入后再进行下游扩散而建立的单一集合种群。然而，最近的证据表明情况更为复杂，涉及在多个地点的引入和双向扩散。为了区分这两种情况，我们分析了近三十年的出现记录以及来自31个地点的372个个体的8592个单核苷酸多态性，并确定了源地点的数量、范围扩张率、种群遗传结构以及基因流动的大小和方向。我们发现入侵扩散起源于多达六个源地点，随后是双向扩散和下游远距离扩散（LDD）事件。我们的结果表明，至少有两个源地点是由主要引入建立的，两个是由LDD事件建立的，而其余的则是由二次引入导致的。一条横穿河流的运河被确定为扩散障碍，导致两岸的入侵动态不同。我们的研究表明，多个地点的异步引入、扩散障碍和环境异质性如何能够在一个看似连续且相互连接的集合种群中导致不同的扩散动态。
