The effects of sexual selection on epidemic outcomes

Sexual selection has two intuitive but overlooked implications for epidemics. First, infectious diseases spread when individuals contact each other. Reproduction is a major driver of contact: mate preferences should affect who contacts whom, and thus parasite transmission opportunity. Sexual selection research shows that choosers prefer mates with high quality ornaments, which generally indicate parasite resistance, but the predicted epidemiological consequence of such contact with more resistant individuals – that transmission slows – is untested. Second, choosers selecting mates that resist parasite infection may benefit indirectly as this increases the parasite resistance of their offspring. If choosers consistently produce offspring with the most genetically resistant mates, population-level parasite resistance should increase through generations: again, untested.I will leverage essential existing knowledge and artificial selection lines of the Trinidadian guppy, its gyrodactylid parasites, and a successful workflow I have developed, to test how variation in female preference affects epidemics in three ways. First, I will run replicate experimental epidemics in groups of individually identified guppies, tracked using machine learning, in which females do, or do not prefer males with larger orange ornaments. These ornaments indicate parasite resistance in this system. Second, I will assay the offspring produced post-epidemic for parasite resistance and paternity. I predict that epidemics in which females prefer ornamented males will be slower, and the offspring produced will be more resistant to parasites. Finally, I will use the results from both experiments to refine a mathematical model. We will validate model predictions with surveys of natural populations known to vary in female preference for males with larger orange ornaments. The resulting framework of how sexual selection affects parasite transmission will improve our predictions of epidemic dynamics.