Nuptial coloration is unaffected by the immune response fibrosis in threespine stickleback

Abstract: To understand why immune traits affect the fitness of its host is an important part of understanding why and how immune responses evolve. In threespine stickleback (Gasterosteus aculeatus), fibrosis is an immune response evolved to combat infection of the tapeworm parasite Schistocephalus solidus. Already known is that fibrosis leads to a reduced mating success for males. Here I investigated whether the immune response, fibrosis, reduces the nuptial coloration of male threespine stickleback (Gasterosteus aculeatus), and whether this is the reason behind the reduction in mating success for fish expressing fibrosis. The software ImageJ was used to analyse the difference in coloration between males with and without a S. solidus infection and with and without fibrosis. Although strong sex and lake differences in coloration were recovered, no evidence that fibrosis causes a reduction in nuptial coloration was found.