Host specificity and diversity of larval digeneans in freshwater fish

点击翻译按钮获取中文摘要

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.