Analysis of trematode parasite communities in fish eye lenses by pyrosequencing of naturally pooled DNA.

Infections by multiple parasite species are common in nature and have important consequences for between-species interactions and coevolutionary dynamics with the host populations. For example, ecological and evolutionary factors underlying the structure of parasite communities determine the range of hosts a parasite can infect and set the basis for both evolution of host defences and parasite virulence, as well as management of diseases. Studies investigating these factors have been facilitated in the recent past by genetic methods, which surmount difficulties of traditional morphological taxonomy in identifying individual parasite species. Here we take a step further and present a novel methodological approach to analyze parasite communities as a whole. We determined the relative frequencies of interspecific SNP alleles by pyrosequencing naturally pooled samples of closely related Diplostomum spp. trematodes infecting eye lenses of freshwater fish. Pyrosequencing allowed us to use naturally pooled community samples (lenses) to increase the sample size and statistical power, without sequencing single parasite specimens. In a case study, we applied this method to analyze the community structure of the eye flukes across fish host species of a freshwater system in Finland. We found that the fish species harboured significantly different parasite communities and that multiple species infections were common. Our study provides an example of how quantitative pyrosequencing can be used to answer evolutionary and ecological questions in natural communities of parasites.