What makes a super-spreader? The genetic architecture and evolutionary constraints on host heterogeneity in pathogen transmission

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Super-spreaders of infectious diseases are the most spectacular examples of host heterogeneity in pathogen transmission. What makes a superspreader? Despite their importance in driving the spread of infections in natural populations, we have a poor understanding of how host genetics contributes to variation in host traits that drive pathogen spread, and almost no understanding of the genetic basis of superspreading. We will address two key questions: 1. How much of host variation in pathogen transmission is explained by their genetics? 2. What are the evolutionary constraints on extreme pathogen shedding phenotypes? Using a naturally-derived population of fruit flies, we will quantify the phenotypic variation in locomotor activity, pathogen shedding, and host susceptibility following infection with the bacterial pathogen Pseudomonas aeruginosa. We will then quantify how much of the phenotypic variance in these traits is explained by among-line genetic variance. In a second experiment, we will experimentally evolve super-shedders. We will start from a genetically variable outbred population and artificially select for extreme pathogen shedding phenotypes and then measure the direct and correlated responses to selection to identify evolutionary constraints on super-shedding individuals.