Host specificity and diversity of larval digeneans in freshwater fish

摘要：幼虫寄生虫是鱼类寄生虫群落的主要组成部分， 由于无法区分物种而未被研究。因此，这些寄生虫通常被视为能够感染许多不相关的鱼类的通才，幼虫物种在构建寄生虫群落中的作用在很大程度上仍然未知。我们的DNA为基础的实地研究表明，幼虫寄生虫社区实际上是高度多样化的，大多数物种是主机特定的，虽然有一些通才。虽然实地研究是必不可少的揭示寄生虫物种的自然分布在宿主社区，这些分布的机制只能通过实验来阐明。我们将使用基于DNA的现场和实验室研究相结合，以确定在四个未研究的家庭从圣劳伦斯河鱼类幼虫寄生虫的自然分布。然后，我们将通过实验感染来测试（1）接触（宿主生态学）和相容性因素（宿主发育）在确定自然界中具有宿主特异性分布的幼虫物种的宿主范围方面的相对重要性，以及（2）Diplostomum spp.，在自然界中许多远亲鱼类中发生的这种变异，在不同的宿主物种中会有所不同，以及这种变异是否可归因于接触或相容性因素。泛生双口吸虫属仅限于单一组织，即眼睛的透镜，混合感染很常见。因此，物种之间可能存在相互作用。我们将研究两种Diplostomum的性能，实验在鱼类宿主（1）暴露于两个物种的同时感染和（2）在连续感染几个星期分开。总之，这些研究将提供详尽的数据与无与伦比的分类分辨率在圣劳伦斯河鱼类幼虫寄生虫的分布，并将阐明生态和系统发育因素的重要性，在确定特定物种的存在，不存在和丰富的不同鱼类宿主。

SUMMARY: Larval parasites form a major component of the parasite community of fish that remains unstudied due to the inability to distinguish between species. Hence, these parasites are typically treated as generalists capable of infecting many unrelated fish species and the role of larvae species in structuring parasite communities remains largely unknown. Our DNA-based field studies demonstrated that the larval parasite community is actually highly diverse and that most species are host specific although there are some generalists. Although field studies are essential for revealing the natural distribution of parasite species within host communities, the mechanisms underlying these distributions can only be elucidated experimentally. We will use a combination of DNA-based field and laboratory studies to determine the natural distribution of larval parasites in four unstudied families of fish from the St. Lawrence River. We will then test, through experimental infections, (1) the relative importance of contact (host ecology) and compatibility factors (host phylogeny) in determining the host range of larval species that have host-specific distributions in nature and (2) whether the performance of Diplostomum spp., which occur in many distantly related fish species in nature, varies in different host species and whether this variation can be attributed to contact or compatibility factors. Generalist Diplostomum spp. are restricted to a single tissue, the lens of the eye, and mixed infections are common Hence, interactions between species are possible. We will investigate the performance of two species of Diplostomum, experimentally in fish hosts (1) exposed to simultaneous infections of two species and (2) in sequential infections sevearl weeks apart. Together, these studies will provide exhaustive data with unequalled taxonomic resolution on the distribution larval parasites in fish in the St. Lawrence River, and will elucidate the importance of ecological and phylogenetic factors in determining the presence, absence and abundance of particular species in different fish hosts.