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1. Higher fat stores contribute to persistence of little brown bat populations with white‐nose syndrome

   https://doi.org/10.1111/1365-2656.12954  

   Cheng, Tina L. ; Gerson, Alexander ; Moore, Marianne S. ; Reichard, Jonathan D. ; DeSimone, Joely ; Willis, Craig K. R. ; Frick, Winifred F. ; Kilpatrick, Auston Marm ; Tate, ed., Ann ( February 2019 , Journal of Animal Ecology)

   The persistence of populations declining from novel stressors depends, in part, on their ability to respond by trait change via evolution or plasticity. White‐nose syndrome (WNS) has caused rapid declines in several North America bat species by disrupting hibernation behaviour, leading to body fat depletion and starvation. However, some populations ofMyotis lucifugusnow persist withWNSby unknown mechanisms.

   We examined whether persistence ofM. lucifiguswithWNScould be explained by increased body fat in early winter, which would allow bats to tolerate the increased energetic costs associated withWNS. We also investigated whether bats were escaping infection or resistant to infection as an alternative mechanism explaining persistence.

   We measured body fat in early and late winter during initialWNSinvasion and 8 years later at six sites where bats are now persisting. We also measured infection prevalence and intensity in persisting populations.

   Infection prevalence was not significantly lower than observed in declining populations. However, at two sites, infection loads were lower than observed in declining populations. Body fat in early winter was significantly higher in four of the six persisting populations than duringWNSinvasion.

   Physiological models of energy use indicated that these higher fat stores could reduceWNSmortality by 58%–70%. These results suggest that differences in fat storage and infection dynamics have reduced the impacts ofWNSin many populations. Increases in body fat provide a potential mechanism for management intervention to help conserve bat populations.

    

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2. Mobility and infectiousness in the spatial spread of an emerging fungal pathogen

   https://doi.org/10.1111/1365-2656.13439  

   Langwig, Kate E. ; White, J. Paul ; Parise, Katy L. ; Kaarakka, Heather M. ; Redell, Jennifer A. ; DePue, John E. ; Scullon, William H. ; Foster, Jeffrey T. ; Kilpatrick, A. Marm ; Hoyt, Joseph R. ( February 2021 , Journal of Animal Ecology)

   Emerging infectious diseases can have devastating effects on host communities, causing population collapse and species extinctions. The timing of novel pathogen arrival into naïve species communities can have consequential effects that shape the trajectory of epidemics through populations. Pathogen introductions are often presumed to occur when hosts are highly mobile. However, spread patterns can be influenced by a multitude of other factors including host body condition and infectiousness.

   White‐nose syndrome (WNS) is a seasonal emerging infectious disease of bats, which is caused by the fungal pathogenPseudogymnoascus destructans. Within‐site transmission ofP. destructansprimarily occurs over winter; however, the influence of bat mobility and infectiousness on the seasonal timing of pathogen spread to new populations is unknown. We combined data on host population dynamics and pathogen transmission from 22 bat communities to investigate the timing of pathogen arrival and the consequences of varying pathogen arrival times on disease impacts.

   We found that midwinter arrival of the fungus predominated spread patterns, suggesting that bats were most likely to spreadP.destructanswhen they are highly infectious, but have reduced mobility. In communities whereP. destructanswas detected in early winter, one species suffered higher fungal burdens and experienced more severe declines than at sites where the pathogen was detected later in the winter, suggesting that the timing of pathogen introduction had consequential effects for some bat communities. We also found evidence of source–sink population dynamics over winter, suggesting some movement among sites occurs during hibernation, even though bats at northern latitudes were thought to be fairly immobile during this period. Winter emergence behaviour symptomatic of white‐nose syndrome may further exacerbate these winter bat movements to uninfected areas.

   Our results suggest that low infectiousness during host migration may have reduced the rate of expansion of this deadly pathogen, and that elevated infectiousness during winter plays a key role in seasonal transmission. Furthermore, our results highlight the importance of both accurate estimation of the timing of pathogen spread and the consequences of varying arrival times to prevent and mitigate the effects of infectious diseases.

    

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3. Environmental transmission of Pseudogymnoascus destructans to hibernating little brown bats

   https://doi.org/10.1038/s41598-023-31515-w  

   Hicks, Alan C. ; Darling, Scott R. ; Flewelling, Joel E. ; von Linden, Ryan ; Meteyer, Carol U. ; Redell, David N. ; White, J. Paul ; Redell, Jennifer ; Smith, Ryan ; Blehert, David S. ; et al ( March 2023 , Scientific Reports)

   Pathogens with persistent environmental stages can have devastating effects on wildlife communities. White-nose syndrome (WNS), caused by the fungusPseudogymnoascus destructans,has caused widespread declines in bat populations of North America. In 2009, during the early stages of the WNS investigation and before molecular techniques had been developed to readily detectP. destructansin environmental samples, we initiated this study to assess whetherP. destructanscan persist in the hibernaculum environment in the absence of its conclusive bat host and cause infections in naive bats. We transferred little brown bats (Myotis lucifugus) from an unaffected winter colony in northwest Wisconsin to twoP. destructanscontaminated hibernacula in Vermont where native bats had been excluded.Infection withP. destructanswas apparent on some bats within 8 weeks following the introduction of unexposed bats to these environments, and mortality from WNS was confirmed by histopathology at both sites 14 weeks following introduction. These results indicate that environmental exposure toP. destructansis sufficient to cause the infection and mortality associated with WNS in naive bats, which increases the probability of winter colony extirpation and complicates conservation efforts.

    

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4. Sex-biased infections scale to population impacts for an emerging wildlife disease

   https://doi.org/10.1098/rspb.2023.0040  

   Kailing, Macy J. ; Hoyt, Joseph R. ; White, J. Paul ; Kaarakka, Heather M. ; Redell, Jennifer A. ; Leon, Ariel E. ; Rocke, Tonie E. ; DePue, John E. ; Scullon, William H. ; Parise, Katy L. ; et al ( March 2023 , Proceedings of the Royal Society B: Biological Sciences)

   Demographic factors are fundamental in shaping infectious disease dynamics. Aspects of populations that create structure, like age and sex, can affect patterns of transmission, infection intensity and population outcomes. However, studies rarely link these processes from individual to population-scale effects. Moreover, the mechanisms underlying demographic differences in disease are frequently unclear. Here, we explore sex-biased infections for a multi-host fungal disease of bats, white-nose syndrome, and link disease-associated mortality between sexes, the distortion of sex ratios and the potential mechanisms underlying sex differences in infection. We collected data on host traits, infection intensity and survival of five bat species at 42 sites across seven years. We found females were more infected than males for all five species. Females also had lower apparent survival over winter and accounted for a smaller proportion of populations over time. Notably, female-biased infections were evident by early hibernation and likely driven by sex-based differences in autumn mating behaviour. Male bats were more active during autumn which likely reduced replication of the cool-growing fungus. Higher disease impacts in female bats may have cascading effects on bat populations beyond the hibernation season by limiting recruitment and increasing the risk of Allee effects. 

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5. Environmental transmission of Pseudogymnoascus destructans to hibernating little brown bats

   https://doi.org/10.1101/2021.07.01.450774  

   Hicks, A. c. ( July 2021 , bioRxiv)

   Pathogens with persistent environmental stages can have devastating effects on wildlife communities. White-nose syndrome (WNS), caused by the fungus Pseudogymnoascus destructans, has caused widespread declines in bat populations of North America. In 2009, during the early stages of the WNS investigation and before molecular techniques had been developed to readily detect P. destructans in environmental samples, we initiated this study to assess whether P. destructans can persist in the hibernaculum environment in the absence of its conclusive bat host and cause infections in naive bats. We transferred little brown bats (Myotis lucifugus) from an unaffected winter colony in northwest Wisconsin to two P. destructans contaminated hibernacula in Vermont where native bats had been excluded. Infection with P. destructans was apparent on some bats within 8 weeks following the introduction of unexposed bats to these environments, and mortality from WNS was confirmed by histopathology at both sites 14 weeks following introduction. These results indicate that environmental exposure to P. destructans is sufficient to cause the infection and mortality associated with WNS in naive bats, which increases the probability of winter colony extirpation and complicates conservation efforts. 

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