Testing for multiple invasion routes and source populations for the invasive brown treesnake (Boiga irregularis) on Guam: implications for pest management

The brown treesnake (Boiga irregularis) population on the Pacific island of Guam has reached iconic status as one of the most destructive invasive species of modern times, yet no published works have used genetic data to identify a source population. We used DNA sequence data from multiple genetic markers and coalescent-based phylogenetic methods to place the Guam population within the broader phylogeographic context of B. irregularis across its native range and tested whether patterns of genetic variation on the island are consistent with one or multiple introductions from different source populations. We also modeled a series of demographic scenarios that differed in the effective size and duration of a population bottleneck immediately following the invasion on Guam, and measured the fit of these simulations to the observed data using approximate Bayesian computation. Our results exclude the possibility of serial introductions from different source populations, and instead verify a single origin from the Admiralty Archipelago off the north coast of Papua New Guinea. This finding is consistent with the hypothesis that B. irregularis was accidentally transported to Guam during military relocation efforts at the end of World War II. Demographic model comparisons suggest that multiple snakes were transported to Guam from the source locality, but that fewer than 10 individuals could be responsible for establishing the population. Our results also provide evidence that low genetic diversity stemming from the founder event has not been a hindrance to the ecological success of B. irregularis on Guam, and at the same time offers a unique ‘genetic opening’ to manage snake density using classical biological approaches.

太平洋关岛的棕树蛇（Boiga irregularis）种群作为现代史上破坏性最强的入侵物种之一，已成为极具标志性的入侵案例，但此前尚无公开研究借助遗传数据确定其来源种群。本研究采用多遗传标记的DNA序列数据与基于溯祖理论的系统发育分析方法，将关岛种群置于棕树蛇原生分布区的系统地理学大框架中开展分析，并检验该岛的遗传变异模式是否符合来自不同来源种群的单次或多次引入事件。本研究同时构建了一系列种群动态情景模型，各模型在关岛入侵后即刻出现的种群瓶颈的有效规模与持续时长上存在差异，并通过近似贝叶斯计算（approximate Bayesian computation）方法评估了各模拟结果与观测数据的契合度。研究结果排除了来自不同来源种群的连续引入的可能性，证实关岛棕树蛇种群的单一来源为巴布亚新几内亚北海岸外的阿德米勒尔蒂群岛（Admiralty Archipelago）。该发现与“二战末期军事转运过程中，棕树蛇被意外带入关岛”的假说相符。种群动态模型对比结果显示，从来源地被转运至关岛的棕树蛇个体不止一只，但最终建立种群的奠基个体数量不足10只。本研究同时证实，奠基事件导致的遗传多样性匮乏并未阻碍棕树蛇在关岛的生态扩张；同时，该结果为利用经典生物防治手段管控蛇类种群密度提供了独特的“遗传学切入点”。