Shared genetic diversity across the global invasive range of the Monk parakeet suggests a common restricted geographic origin and the possibility of convergent selection

While genetic diversity is hypothesized to be an important factor explaining invasion success, there is no consensus yet on how variation in source populations or demographic processes affects invasiveness. We used mitochondrial DNA haplotypic and microsatellite genotypic data to investigate levels of genetic variation and reconstruct the history of replicate invasions on three continents in a globally invasive bird, the monk parakeet (Myiopsitta monachus). We evaluated whether genetic diversity at invasive sites could be explained by (i) the native source populations from which they were derived and (ii) demographic bottlenecks during introduction. Genetic data indicated a localized source area for most sampled invasive populations, with limited evidence for admixing of native source populations. This pattern largely coincides with historical data on pet trade exports. However, the invasive populations are genetically more similar than predicted from the export data alone. The extent of bottleneck effects varied among invasive populations. The observed low genetic diversity, evidence of demographic contraction and restricted source area do not support the hypothesis that invasion is favoured by the mixing and recombining of genetic variation from multiple source populations. Instead, they suggest that reduced genetic variation through random processes may not inhibit successful establishment and invasion in this species. However, convergent selection across invasive sites could also explain the observed patterns of reduction and similarity in genetic variation and/or the restricted source area. In general, the alternative explanation of intraspecific variation in invasive potential among genotypes or geographic areas is neglected, but warrants more attention as it could inform comparative studies and management of biological invaders.

尽管遗传多样性被认为是解释物种入侵成功的关键因子，但学界对于源种群变异或种群动态过程如何影响入侵性尚未形成统一共识。本研究以全球入侵鸟类和尚鹦鹉（Myiopsitta monachus）为研究对象，借助线粒体DNA单倍型与微卫星基因型数据，探究其遗传变异水平，并重构其在三大洲的重复入侵历史。我们评估了入侵种群的遗传多样性是否可通过两类因素进行解释：其一为其起源的本土源种群，其二为引种过程中经历的种群瓶颈。遗传数据分析结果显示，绝大多数被采样的入侵种群均具有局限的源种群分布范围，且几乎未发现本土源种群间发生基因混合的证据，这一模式与宠物贸易出口的历史记录大体吻合。但相较仅基于宠物贸易出口数据的预测结果，入侵种群间的遗传相似性更高。不同入侵种群的瓶颈效应强度存在显著差异。本次研究观测到的低遗传多样性、种群收缩证据以及源种群范围受限的现象，均不支持“多源种群的遗传变异混合与重组可促进物种入侵”这一假说。与之相反，研究结果表明，由随机过程导致的遗传多样性降低，并未阻碍和尚鹦鹉的成功定殖与入侵过程。不过，入侵区域间的趋同选择作用，同样可以解释观测到的遗传多样性降低、种群间遗传相似性升高以及源种群范围受限的现象。总体而言，“不同基因型或地理区域的入侵潜能存在种内变异”这一替代假说常被忽视，但该假说值得进一步关注——因其可为生物入侵者的比较研究与管理防控工作提供重要参考。