Identification of virulence genes in Schistocephalus solidus

Whilst the three-spined stickleback (Gasterosteus aculeatus) and its various macroparasites have become increasingly used to investigate the genetic basis of parasitic evolutionary pressure and its effects on immunocompetence the majority of studies focus on the stickleback. In this study the focus was on Schistocephalus solidus, a tapeworm using the three-spined stickleback as an obligate intermediate host. The aim was to determine particular genes that could be responsible for host manipulation and virulence levels within the fish. Using a fully crossed infection experiment with German and Norwegian populations we confirmed possible virulence optima for sympatric combinations and noticed virulence mismatch between allopatric ones. German worms in Norwegian fish failed to reach this optimum whilst Norwegian worms in German fish seemed to overshoot it and thus overexploit their fish hosts. To identify the genes involved we initially developed the first annotated draft transcriptome library for S. solidus. Then using differential gene expression counts for a select few worms from each combination we identified candidate genes that could be responsible for such mismatches. Finally, we developed primer pairs for 32 selected genes and ran multiplexed RTqPCR on all 92 S. solidus in our experiment using the Fluidigm platform. The combined results including the developing transcriptome library and working primers give us not only an indication of virulence genes that S. solidus uses but also provides a solid platform for future studies on the S. solidus/three-spined stickleback interactome.