Hitching Pseudoxiphophorus bimaculatus

We studied flatworm parasites of the genus Gyrodactylus associated with twospot livebearer Pseudoxiphophorus bimaculatus both in this host’s native distribution in the Gulf of Mexico (Atlantic Ocean) versant, as well as in its invasive range across the continental divide, on the Pacific Ocean watershed. We surveyed 12 river basins, six on each slope of the continent, and recorded strongly overdispersed parasite distributions, both in terms of localities within basins and on fish hosts. Six gyrodactylid species were previously known to infect this poeciliid host, and we add five taxa to the list, three known and two undescribed species. From the 11 parasite species we characterized molecularly (cox 2 mDNA and ITS rDNA 43 sequences), 9–10 were recorded in river basins draining into the Atlantic, and only four in rivers flowing into the Pacific. Only one species, Gyrodactylus takoke, was recorded frequently on both sides of the country, and cox 2 haplotype networks suggest that parasites co-translocated with their fish hosts originated from the central Gulf of Mexico slope and successfully invaded two river basins draining into the Pacific. Our preliminary data do not allow proper testing, but we hypothesize that following the translocation of P. bimaculatus across the continental divide of Mexico, different types of host-parasite interactions (enemy release, spill-over and spill-back) may involve particular parasite species, some of which are known to be pathogenic

本研究针对与双斑活胎鳉（Pseudoxiphophorus bimaculatus）相关的三代虫属（Gyrodactylus）扁形动物寄生虫开展调查，覆盖该宿主的原生分布区——墨西哥湾（大西洋海域）沿岸，以及其跨越大陆分水岭的太平洋流域入侵范围。本研究共调查了12个河流流域，大陆两侧各6个，结果发现寄生虫种群呈现强烈的聚集分布特征，该特征同时体现在流域内的采样点位间与宿主鱼个体间。此前已知有6种三代虫科寄生虫可寄生该花鳉科宿主，本研究新增5个分类单元，其中3个为已知物种，2个为未描述新种。本研究对11种寄生虫进行了分子鉴定（基于线粒体cox2基因与核糖体ITS rDNA序列，共获得43条序列），其中9至10种记录于注入大西洋的流域，仅4种见于注入太平洋的河流。仅塔科克三代虫（Gyrodactylus takoke）在大陆两侧均有频繁检出，cox2单倍型网络分析显示，随宿主鱼一同转移的寄生虫起源于墨西哥湾中部沿岸，并成功入侵了两个注入太平洋的流域。本研究的初步数据无法支撑充分验证，但我们提出假说：当双斑活胎鳉跨越墨西哥大陆分水岭发生扩散后，不同类型的宿主-寄生虫互作（包括天敌释放、溢出感染与回流感染）可能涉及特定的寄生虫物种，其中部分物种已被证实具有致病性。