Context- and sex-dependent links between sire sexual success and offspring pathogen resistance

Sexual selection has been proposed to promote genetic variants that improve resistance to pathogens (a variant of the "good genes" hypothesis). Two key mechanisms linking sexual success and pathogen resistance have been proposed: the "condition-dependent" scenario, where general health improves both sexual traits and pathogen resistance, and the "context-dependent" scenario, where resistance to specific pathogens benefits sexual success only in certain environments. Few studies distinguish between these two mechanisms. Here, we used Drosophila melanogaster in an experiment designed to test for additive genetic relationship between males' sexual success and the resistance of its offspring to the fungal pathogen Metarhizium brunneum, and to investigate if this relationship depends on pathogen exposure during sexual selection as well as on offspring sex. In the absence of the pathogen, more sexually successful males sired less pathogen-resistant offspring, whereas no relationship was detected when sires competed for paternity after pathogen exposure. For daughters, the relationship tended to be negative irrespective of sire's pathogen exposure. Thus, while we confirmed that sexual selection may act on genes affecting resistance in a context- and sex-dependent manner, we found no circumstances under which it promoted resistance, in contradiction to the "good genes" hypothesis.