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，这一群落尚未得到研究。因此，这些寄生虫通常被视为多面手，能够感染许多不相关的鱼类，而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。我们基于dna的实地研究表明，幼虫寄生群落实际上是高度多样化的，尽管有一些通用性，但大多数物种都是宿主特异性的。虽然实地研究对于揭示寄主群落内寄生虫物种的自然分布是必不可少的，但这些分布的机制只能通过实验来阐明。我们将采用基于dna的实地和实验室研究相结合的方法，确定圣劳伦斯河四个未研究的鱼类科中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（宿主系统发育）在确定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；(2)在自然界中许多远亲鱼类中发生的Diplostomum spp.的表现是否在不同的宿主物种中有所不同，以及这种变化是否可归因于接触或相容性因素。多面手双口虫局限于单一组织，即眼睛的晶状体，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，实验在鱼宿主中(1)暴露于两种物种同时感染和(2)相隔数周的连续感染。总之，这些研究将为圣劳伦斯河鱼类幼虫寄生虫的分布提供详尽的数据和无与伦比的分类学分辨率，并将阐明生态和系统发育因素在确定不同鱼类宿主中特定物种的存在、缺失和丰度方面的重要性。

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.