BackgroundThe sea lamprey (Petromyzon marinus) is a jawless vertebrate that parasitizes fish as an adult and, with overfishing, was responsible for the decline in lake trout (Salvelinus namaycush) populations in the Great Lakes. While laboratory studies have looked at the rates of wounding on various fish hosts, there have been few investigations on the physiological effects of lamprey wounding on the host. In the current study, two morphotypes of lake trout, leans and siscowets, were parasitized in the laboratory by sea lampreys and the liver transcriptomes of parasitized and nonparasitized fish were analyzed by RNA-seq (DESeq2 and edgeR) to determine which genes and gene pathways (Ingenuity Pathway Analysis) were altered by lamprey parasitism.ResultsOverall, genes encoding molecules involved in catalytic (e.g., enzymatic) and binding activities (factors and regulators) predominated the regulated gene lists. In siscowets, the top upregulated gene was growth arrest and DNA-damage-inducible protein and for leans it was interleukin-18-binding protein. In leans, the most significantly downregulated gene was UDP-glucuronosyltransferase 2A2 - DESeq2 or phosphotriesterase related - edgeR. For siscowets, the top downregulated gene was C-C motif chemokine 19 - DESeq2 or GTP-binding protein Rhes - edgeR. Gene pathways associated with inflammatory-related responses or factors (cytokines, chemokines, oxidative stress, apoptosis) were regulated following parasitism in both morphotypes. However, pathways related to energy metabolism (glycolysis, gluconeogenesis, lipolysis, lipogenesis) were also regulated. These pathways or the intensity or direction (up/downregulation) of regulation were different between leans and siscowets. Finally, one of the most significantly downregulated pathways in both leans and siscowets was the kynurenine (tryptophan degradation) pathway.ConclusionsThe results indicate a strong transcriptional response in the lake trout to lamprey parasitism that entails genes involved in the regulation of inflammation and cellular damage. Responses to energy utilization as well as hydromineral balance also occurred indicating an adjustment in the host to energy demands and osmotic imbalances during parasitism. Given the role of the kynurenine pathway in promoting immunotolerance in mammals, the downregulation observed in this pathway during parasitism may signify an attempt by the host to inhibit any feedback suppression of the immune response to the lamprey.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2959-9) contains supplementary material, which is available to authorized users.

24Assessment of stress from varied sources are usually evaluated on individuals derived from a 25 single population, and are assumed to represent all populations of that species. However, recent 26 research has identified intraspecies variations in the stress response, which may be mediated by 27 life history. We examined how life history can influence the physiological responses to an acute 28 stress event by evaluating sea lamprey (Petromyzon marinus) parasitism response in two lake 29 trout (Salvelinus namaycush) morphotypes-the lean and siscowet. The morphotypes differ such 30 that the lean grows faster, is more fecund, and has a shorter life span. In contrast the siscowet 31 grows slower, is older at maturity, and lives longer. Our study compared long-term parasitism 32 responses between wild leans and siscowets in Lake Superior and immediate responses in 33 laboratory parasitism trials using lake trout reared under common environmental conditions. 34Leans, but not siscowets, showed changes in steroid binding protein function, and weak evidence 35 of parasitism gigantism in response to parasitism. Both morphotypes showed indications of 36 reproductive endocrine alterations in response to parasitism. Our results demonstrate intraspecies 37 variation in physiological stressor response, which is mediated by life history differences that 38 could potentially have differential population implications. 39 40 41 42 43 44 45 46