Comparative transcriptomics gives insights into the evolution of parasitism in Strongyloides nematodes at the genus, subclade and species level.

Strongyloides spp., gastrointestinal nematode parasites of humans and other animals, have genetically identical parasitic and free-living adult life cycle stages. This is an almost unique feature amongst nematodes and comparison of these two stages can provide insights into the genetic basis and evolution of Strongyloides nematode parasitism. Here, we present RNAseq data for S. venezuelensis, a parasite of rodents, and identify genes that are differentially expressed in parasitic and free-living life cycle stages. Comparison of these data with analogous RNAseq data for three other Strongyloides spp., has identified key protein-coding gene families with a putative role in parasitism including WAGO-like Argonautes (at the genus level) and speckle-type POZ-like coding genes (S. venezuelensis-S. papillosus phylogenetic subclade level). Diverse gene families are uniquely upregulated in the parasitic stage of all four Strongyloides species, including a distinct upregulation of genes encoding cytochrome P450 in S. venezuelensis, suggesting some diversification of the molecular tools used in the parasitic life cycle stage among individual species. Together, our results identify key gene families with a putative role in Strongyloides parasitism or features of the parasitic life cycle stage, and deepen our understanding of parasitism evolution among Strongyloides species.