Mating strategies explain sex-biased infections in an emerging fungal disease

Abstract

Mating dynamics can govern species impacts from novel pressures by influencing demographic processes that affect mortality risk. Understanding how mating systems shape interactions among individuals can improve predictions of the effects of environmental change on populations. Here, we examined sex differences in mating phenology in populations where mating activity coincides with exposure to P. destructans, a lethal fungal pathogen, to understand how reproductive strategies contribute to disease impacts. As P. destructans can replicate only at the cool temperatures at which bats hibernate, we expected differences in activity among sexes to modify disease dynamics. We used passive antenna systems installed at the entrances of hibernacula to characterize activity patterns of bats impacted by white-nose syndrome. We also measured pathogen loads on bats during autumn mating and early hibernation to assess how infection severity changed according to host phenology. We found that females spent fewer days active during autumn, arrived after males, and were primarily active on the warmest nights. Males remained highly active throughout the mating period and later in autumn than females. Importantly, these differences in mating phenology likely led to more severe infections in females during early hibernation as male activity and thus warm body temperatures inhibited pathogen growth. Differences in activity between sexes and in the transition from swarm to hibernation likely reflects males maximizing their mating opportunities while females conserve energy to meet the cost of spring migration and reproduction. More broadly, our results show how mating phenology can contribute to sex-biased impacts of a novel disease and highlight the value of understanding species mating systems to anticipate the impacts of environmental change.