Data from: Invasion of the Hawaiian Islands by a parasite infecting imperiled stream fishes

Points of origin and pathways of spread are often poorly understood for introduced parasites that drive disease emergence in imperiled native species. Co-introduction of parasites with non-native hosts is of particular concern in remote areas like the Hawaiian Islands, where the introduced nematode Camallanus cotti has become the most prevalent parasite of at-risk native stream fishes. In this study, we evaluated the prevailing hypothesis that C. cotti entered the Hawaiian Islands with poeciliid fishes from the Americas, and spread by translocation of poeciliid hosts across the archipelago for mosquito control. We also considered the alternative hypothesis of multiple independent co-introductions with host fishes originating from Asia. We inferred conduits of introduction and spread of C. cotti across the archipelago from geographic patterns of mtDNA sequence variation and allelic variation across 11 newly developed microsatellite markers. The distribution of haplotypes suggests that C. cotti spread across the archipelago following an initial introduction on O'ahu. Approximate Bayesian Computation modeling and allelic variation also indicate that O'ahu is the most likely location of introduction, from which C. cotti dispersed to Maui followed by spread to the other islands in the archipelago. Evidence of significant genetic structure across islands indicates that contemporary dispersal is limited. Our findings parallel historical records of non-native poeciliid introductions and suggest that remediating invasion hotspots could reduce the risk of infection in native stream fishes, which illustrates how inferences on parasite co-introductions can improve conservation efforts by guiding responses to emerging infectious disease in species of concern.

对于那些导致濒危本土物种出现传染病的外来寄生虫，其起源与传播路径往往尚未被充分阐明。寄生虫与非本土宿主的共引入事件在夏威夷群岛这类偏远区域尤为值得关注：目前，外来线虫Camallanus cotti已成为当地受胁本土溪流鱼类最普遍的寄生虫。本研究针对两项核心假说展开验证：其一为主流假说，即Camallanus cotti随源自美洲的花鳉科鱼类传入夏威夷群岛，并因人类为防控蚊虫而跨群岛转运花鳉宿主实现扩散；其二为替代假说，即该线虫曾多次独立与源自亚洲的宿主鱼类完成共引入。我们依托11个新开发的微卫星标记（microsatellite markers）的等位基因变异数据，结合线粒体DNA（mtDNA）序列变异的地理分布模式，推断了Camallanus cotti在该群岛内的引入与传播路径。单倍型分布结果显示，Camallanus cotti经初始定殖瓦胡岛后，在群岛范围内实现扩散。近似贝叶斯计算（Approximate Bayesian Computation）建模与等位基因变异分析同样表明，瓦胡岛是最有可能的初始引入位点，该线虫从这里扩散至毛伊岛，随后进一步传播至群岛内其余各岛屿。群岛内各岛屿间存在显著遗传结构的证据显示，当代扩散过程受到明显限制。本研究结果与外来花鳉科鱼类引入的历史记录相互印证，同时提示，针对入侵热点开展修复工作可降低本土溪流鱼类的感染风险——这一发现阐明了针对寄生虫共引入的推断，可通过指导受关注物种新发传染病的应对策略，助力相关保护工作的推进。