Sublethal immune, endocrine, and bioenergetics responses to sea lamprey parasitism in two lake trout morphotypes from Lake Superior

Sea lamprey (Petromyzon marinus) are an invasive species in the Great Lakes and have caused extensive mortality to native lake trout (Salvelinus namaycush). Past research has focused primarily on the lethal effects of parasitism and very little is known about the sublethal effects. This study examined lake trout response to sublethal sea lamprey parasitism by measuring parameters related to immune modulation, endocrine disruption, and bioenergetics changes (growth and reproduction). I also compared two Lake Superior lake trout morphotypes (lean and siscowet) to determine how life history influences parasitism responses. Leans and siscowets are partially bathymetrically isolated in Lake Superior and have genetically-based morphological differences, including higher muscle lipid concentrations in siscowets. On both morphotypes, I measured immediate responses to sea lamprey attacks through a laboratory experiment and long-term, cumulative effects through Lake Superior field studies. Sublethal sea lamprey parasitism was associated with endocrine disruption (suppressed plasma testosterone and pituitary follicle-stimulating hormone [FSH]) in the lean and siscowet morphotypes. Parasitized siscowets showed indications of immune-related modulation (hepatosomatic index increase with parasitism duration and differential regulation of immune-related genes) as an immediate response to parasitism and a trend towards decreased muscle lipid concentrations in wild populations. These results support the hypothesis that sea lamprey parasitism affects immune, endocrine, and bioenergetics related parameters, and that parasitism response is influenced by life history.