SRA

The three-spined stickleback (Gasterosteus aculeatus) has repeatedly colonized and adapted to diverse freshwater habitats since the last glaciation. Among those freshwater habitats, adjacent lake and river populations harbour distinct parasite communities, a recurring ecological difference proposed to drive adaptive differentiation between lake and river stickleback ecotypes. To study the rapid adaptation of sticklebacks to lake and river habitats, we analysed gene expression profiles of 77 whole-transcriptome libraries of two immune-relevant tissues, the head kidney and the spleen, obtained from wild-caught sticklebacks of the two habitat types across multiple geographic locations. Differential expression analyses identified 189 genes showing statistically significant habitat-specific expression patterns among the three European locations. Among those genes, 15 genes are annotated with putative immune functions, and 50 have been experimentally associated with immune-responses in sticklebacks, reinforcing the hypothesis that parasites contribute to adaptive evolution of lake and river sticklebacks. Comparing expression profiles of European sticklebacks to populations in similar habitats in North America, five genes exhibited habitat-specific expression across continents.