COS 259-5 - Asynchronous sex-based reproduction in bats affected by a virulent fungal pathogen

Abstract: Life history strategies describe the collection of traits organisms express to optimize fitness, including how and when limited energy is allocated among fitness-related functions, such as survival, reproduction, and growth. Life history strategies have diverged between sexes through processes of sexual and natural selection in many taxa. Accordingly, tradeoffs between energy conservation and reproduction can be asynchronous between females and males and give rise to seasonally dependent sexually dimorphic behaviors and physiology. Life history-based traits importantly shape sex-specific vulnerabilities to environmental stressors, including susceptibility to novel pathogens. White-nose syndrome (WNS) is an emerging fungal disease of bats that has caused widespread collapse of North American populations. Importantly, bat hosts are initially exposed to the pathogen during autumn mating, however, energy for reproduction is asynchronously invested between sexes. Therefore, reproductive behaviors driven by asynchrony in energy allocation could contribute to observed differences in disease outcomes between female and male bats. Here, we explored sex-based behaviors of Myotis lucifugus during the mating period to understand the role of autumn activity in bat infections.

We used radio-frequency identification (RFID) systems consisting of a passive antenna and automated data-logger at the entrances of three large hibernacula in the upper Midwest to monitor activity of individuals tagged with a passive integrated transponder (PIT). We estimated the mating period (i.e., begin and end) for females and males and quantified the occurrence of newly arriving individuals throughout autumn by sex across multiple years. We found that females arrive to mate later than males but end their mating activity soon after arriving to sites. Most male bats were present by the earliest dates of autumn and remained active longer, whereas new females arrived more consistently throughout autumn. These differences in mating activity likely reflect males’ strategy to increase fitness by mating with newly arriving females, and females’ priority to conserve energy by starting hibernation over maximizing mates. Increased use of hibernation during autumn compared to males resulted in higher winter infections in females that lead to higher mortality. More broadly these findings highlight the potential for sex-specific tactics of fitness optimization to influence sex-biased impacts to novel environmental stressors, such as emerging infectious disease.