Invaded Invaders: Infection of Invasive Brown Treesnakes on Guam by an Exotic Larval Cestode with a Life Cycle Comprised of Non-Native Hosts

BackgroundMultiple host introductions to the same non-native environment have the potential to complete life cycles of parasites incidentally transported with them. Our goal was to identify a recently detected parasitic flatworm in the invasive Brown Treesnake (Boiga irregularis) on the remote Pacific island of Guam. We considered possible factors influencing parasite transmission, and tested for correlations between infection status and potential indicators of host fitness. We used genetic data from the parasite and information about the native ranges of other possible non-native hosts to hypothesize how it arrived on Guam and how its life cycle may be currently supported.MethodsWe identified the parasite by comparing larval morphology and mtDNA sequences with other Pseudophyllid tapeworms. We assessed probability of infection in individual snakes using logistic regression and examined different factors influencing presence of parasites in hosts.ResultsWe identified the parasite as the pseudophyllid cestode Spirometra erinaceieuropaei, with all sampled worms from multiple snakes sharing a single mtDNA haplotype. Infection appears to be limited to the only freshwater watershed on the island, where infection prevalence was high (77.5%). Larger snakes had a higher probability of being infected, consistent with the chronic nature of such infections. While infection status was positively correlated with body condition, infected snakes tended to have lower intra-peritoneal fat body mass, potentially indicating a negative effect on energy stores.ConclusionsWe discovered that B. irregularis inhabiting a small area of forested habitat in a freshwater watershed on Guam are often infected by a novel parasite of Asian origin. While further work is needed, this species of Spirometra, itself a non-native species, likely depends on a suite of recently introduced hosts from different parts of the world to complete the life cycle. This baseline study provides little evidence of any effects on host fitness, but additional data are needed to more thoroughly explore the consequences of infection in this invasive snake population.研究背景：多次将宿主类群引入同一非原生环境中，有可能使随宿主偶然传入的寄生虫完成其生活周期。本研究旨在对太平洋偏远岛屿关岛的入侵物种棕树蛇（Boiga irregularis）体内近期发现的寄生扁形动物进行物种鉴定。我们分析了影响寄生虫传播的潜在因素，并检验了宿主感染状态与宿主健康潜在指标之间的相关性。我们利用寄生虫的遗传数据以及其他潜在非原生宿主的原生分布范围信息，对该寄生虫抵达关岛的途径以及当前维持其生活周期的机制提出假说。研究方法：通过比对幼虫形态与线粒体DNA（mtDNA）序列，并与其他假叶目绦虫（Pseudophyllid tapeworms）进行参照，完成了该寄生虫的物种鉴定。我们采用逻辑回归模型评估了单只棕树蛇的感染概率，并分析了影响宿主体内寄生虫定植的各类因素。研究结果：经鉴定，该寄生虫为假叶目绦虫（Pseudophyllid cestode）猬迭宫绦虫（Spirometra erinaceieuropaei），且所有采自多条棕树蛇的样本蠕虫共享单一线粒体DNA单倍型。该寄生虫的感染范围似乎局限于岛上唯一的淡水流域，该区域的感染率高达77.5%。体型更大的棕树蛇感染概率更高，这与这类感染的慢性病程特征相符。尽管感染状态与宿主身体状况呈正相关，但感染的棕树蛇往往具有更低的腹腔脂肪体质量，这可能暗示感染对宿主能量储备存在负面影响。研究结论：本研究发现，栖息于关岛某淡水流域内小片森林生境中的棕树蛇（Boiga irregularis，后文简称B. irregularis）常被一种源自亚洲的新型寄生虫感染。尽管仍需开展进一步研究，但该猬迭宫绦虫（Spirometra）本身属于非原生物种，其完成生活周期可能依赖于近期从全球不同区域引入的一系列宿主类群。本项基线研究未发现该寄生虫对宿主健康存在显著影响的证据，但仍需获取更多数据，以更全面地探究感染对该入侵蛇类种群的后续影响。