Sex-biased infections and mortality in a multi-host fungal pathogen of bats

Macy Kailing, Biological Sciences, Virginia Tech, Blacksburg, VA, Joseph R. Hoyt and Kate E. Langwig, Department of Biological Sciences, Virginia Tech, Blacksburg, VA, A. Marm Kilpatrick, Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA

Background/Question/Methods
Emerging infectious diseases are a key threat to wildlife and understanding disease dynamics within populations is fundamental for the conservation of impacted species. Intersex differences in infection are widely observed across disease systems and may have consequences for host populations’ recovery. We explored sex-biased infections of bat species impacted by an emerging fungal disease, white-nose syndrome, and evaluated disease-associated differences in mortality between sexes and potential effects on population structure. We collected fungal swabs, morphometrics, and environmental data from five species of hibernating bats at 43 sites spanning the eastern and midwestern U.S. to characterize infections and host traits over the course of an annual outbreak. We used RFID systems installed at the entrances of hibernation sites and PIT tagged bats to estimate individual activity to determine the role of activity variation between sexes in contributing to differences in infections. We predicted males were more likely to be infected and suffer from more severe infections than females as males are most commonly observed as the sicker sex in other disease systems.
Results/Conclusions
Contrary to our prediction, we found that females had consistently higher infection prevalence and suffered from more severe infections than male conspecifics when there was a clear sex-bias. In addition, we found females were less likely than males to survive their infections and accounted for a smaller proportion of populations over time. Notably, the female-bias in prevalence and infection severity was already evident in early hibernation, suggesting that male and female dynamics prior to hibernation may play an important role in shaping annual epidemics of white-nose syndrome. We found that male bats were more active in the fall than female bats. Longer periods of euthermia in the fall may inhibit fungal growth, enabling males to reduce infections relative to female bats. Higher impacts on females may have cascading effects on populations that extend the consequences of disease beyond the periods when transmission is highest by limiting recruitment and increasing the risk of Allee effects.