Sex and hibernaculum temperature predict survivorship in white-nose syndrome affected little brown myotis (Myotis lucifugus)

Contact-independent exposure to Rhodococcus rhodochrous DAP96253 volatiles does not improve the survival rate of Myotis lucifugus (little brown bats) affected by White-nose Syndrome

Since the emergence of White-nose Syndrome, a fungal disease in bats, caused by Pseudogymnoascus destructans, hibernating populations of little brown bats (Myotis lucifugus) have declined by 70-90% within P. destructans positive hibernacula. To reduce the impact of White-nose Syndrome to North American little brown bat populations we evaluated if exposure to volatile organic compounds produced by induced cells from Rhodococcus rhodochrous strain DAP96253 could improve the overwinter survival of bats infected by P. destructans. Two simultaneous field treatment trials were conducted at natural hibernacula located in Rockcastle and Breckinridge counties, Kentucky, USA. A combined total of 120 little brown bats were randomly divided into control groups (n = 60) which were not exposed to volatile organic compounds and treatment groups (n = 60) which were exposed to volatile organic compounds produced by non-growth, fermented cell paste composed of R. rhodochrous strain DAP96253 cells. Cox proportional hazard models revealed a significant decreased survival at the Rockcastle field trial site but not the Breckinridge field site. At the Breckinridge hibernacula, overwinter survival for both treatment and control groups were 60%. At the Rockcastle hibernacula, Kaplan-Meier survival curves indicated significantly increased overwinter survival of bats in the control group (43% survived) compared to the treatment group (20% survived). Although complete inhibition of P. destructans by volatile organic compounds produced by induced R. rhodochrous strain DAP96253 cells was observed in vitro studies, our results suggest that these volatile organic compounds do not inhibit P. destructans in situ and may promote P. destructans growth.

COULD WHITE-NOSE SYNDROME MANIFEST DIFFERENTLY IN MYOTIS LUCIFUGUS IN WESTERN VERSUS EASTERN REGIONS OF NORTH AMERICA? A REVIEW OF FACTORS

White-nose syndrome (WNS) has notably affected the abundance of Myotis lucifugus (little brown myotis) in North America. Thus far, substantial mortality has been restricted to the eastern part of the continent where the cause of WNS, the invasive fungus Pseudogymnoascus destructans, has infected bats since 2006. To date, the state of Washington is the only area in the Western US or Canada (the Rocky Mountains and further west in North America) with confirmed cases of WNS in bats, and there the disease has spread more slowly than it did in Eastern North America. Here, we review differences between M. lucifugus in western and eastern parts of the continent that may affect transmission, spread, and severity of WNS in the West and highlight important gaps in knowledge. We explore the hypothesis that western M. lucifugus may respond differently to WNS on the basis of different hibernation strategies, habitat use, and greater genetic structure. To document the effect of WNS on M. lucifugus in the West most effectively, we recommend focusing on maternity roosts for strategic disease surveillance and monitoring abundance. We further recommend continuing the challenging work of identifying hibernation and swarming sites to better understand the microclimates, microbial communities, and role in disease transmission of these sites, as well as the ecology and hibernation physiology of bats in noncavernous hibernacula.

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

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.

Temperature shifts associated with bat arousals during hibernation inhibit the growth of Pseudogymnoascus destructans

Temperature is a critically important factor in many infectious disease systems, because it can regulate responses in both the host and the pathogen. White-nose syndrome (WNS) in bats is a severe infectious disease caused by the temperature-sensitive fungus, Pseudogymnoascus destructans (Pd). One feature of WNS is an increase in the frequency of arousal bouts (i.e. when bat body temperatures are elevated) in Pd-infected bats during hibernation. While several studies have proposed that increased frequency of arousals may play a role in the pathophysiology of WNS, it is unknown if the temperature fluctuations might mediate Pd growth. We hypothesized that exposure to a high frequency of elevated temperatures would reduce Pd growth due to thermal constraints on the pathogen. We simulated the thermal conditions for arousal bouts of uninfected and infected bats during hibernation (fluctuating from 8 to 25°C at two different rates) and quantified Pd growth in vitro. We found that increased exposure to high temperatures significantly reduced Pd growth. Because temperature is one of the most critical abiotic factors mediating host-pathogen interactions, resolving how Pd responds to fluctuating temperatures will provide insights for understanding WNS in bats and other fungal diseases.

Changes in hibernating tricolored bat (Perimyotis subflavus) roosting behavior in response to white-nose syndrome

Understanding animals' behavioral and physiological responses to pathogenic diseases is critical for management and conservation. One such disease, white‐nose syndrome (WNS), has greatly affected bat populations throughout eastern North America leading to significant population declines in several species. Although tricolored bat (Perimyotis subflavus) populations have experienced significant declines, little research has been conducted on their responses to the disease, particularly in the southeastern United States. Our objective was to document changes in tricolored bat roost site use after the appearance of WNS in a hibernaculum in the southeastern U.S. and relate these to microsite temperatures, ambient conditions, and population trends. We censused a tricolored bat hibernaculum in northwestern South Carolina, USA, once each year between February 26 and March 2, 2014–2021, and recorded species, section of the tunnel, distance from the entrance, and wall temperature next to each bat. The number of tricolored bats in the hibernaculum dropped by 90.3% during the first 3 years after the arrival of WNS. However, numbers stabilized and slightly increased from 2018 to 2021. Prior to the arrival of WNS, 95.6% of tricolored bats roosted in the back portion of the tunnel that was the warmest. After the arrival of WNS, we observed a significant increase in the proportion of bats using the front, colder portions of the tunnel, particularly during the period of population stabilization and increase. Roost temperatures of bats were also positively associated with February external temperatures. Our results suggest that greater use of the colder sections of the tunnel by tricolored bats could have led to increased survival due to slower growth rates of the fungus that causes WNS in colder temperatures or decreased energetic costs associated with colder hibernation temperatures. Thus, management actions that provide cold hibernacula may be an option for long‐term management of hibernacula, particularly in southern regions.

Host traits and environment interact to determine persistence of bat populations impacted by white-nose syndrome

Emerging infectious diseases have resulted in severe population declines across diverse taxa. In some instances, despite attributes associated with high extinction risk, disease emergence and host declines are followed by host stabilisation for unknown reasons. While host, pathogen, and the environment are recognised as important factors that interact to determine host-pathogen coexistence, they are often considered independently. Here, we use a translocation experiment to disentangle the role of host traits and environmental conditions in driving the persistence of remnant bat populations a decade after they declined 70-99% due to white-nose syndrome and subsequently stabilised. While survival was significantly higher than during the initial epidemic within all sites, protection from severe disease only existed within a narrow environmental space, suggesting host traits conducive to surviving disease are highly environmentally dependent. Ultimately, population persistence following pathogen invasion is the product of host-pathogen interactions that vary across a patchwork of environments.

Experimental inoculation trial to determine the effects of temperature and humidity on White-nose Syndrome in hibernating bats

Disease results from interactions among the host, pathogen, and environment. Inoculation trials can quantify interactions among these players and explain aspects of disease ecology to inform management in variable and dynamic natural environments. White-nose Syndrome, a disease caused by the fungal pathogen, Pseudogymnoascus destructans (Pd), has caused severe population declines of several bat species in North America. We conducted the first experimental infection trial on the tri-colored bat, Perimyotis subflavus, to test the effect of temperature and humidity on disease severity. We also tested the effects of temperature and humidity on fungal growth and persistence on substrates. Unexpectedly, only 37% (35/95) of bats experimentally inoculated with Pd at the start of the experiment showed any infection response or disease symptoms after 83 days of captive hibernation. There was no evidence that temperature or humidity influenced infection response. Temperature had a strong effect on fungal growth on media plates, but the influence of humidity was more variable and uncertain. Designing laboratory studies to maximize research outcomes would be beneficial given the high costs of such efforts and potential for unexpected outcomes. Understanding the influence of microclimates on host-pathogen interactions remains an important consideration for managing wildlife diseases, particularly in variable environments.

The Milieu Souterrain Superficiel as hibernation habitat for bats: implications for white-nose syndrome

Recent studies have revealed that western populations of little brown bats (Myotis lucifugus) in North America exhibit different hibernation behavior than their eastern counterparts. Understanding these differences is essential for assessing the risk white-nose syndrome (WNS) poses to western bat populations. We used acoustic monitoring and radiotelemetry to study the overwintering behavior of little brown bats near Juneau, Alaska during 2011-2014. Our objectives were to identify the structures they use for hibernation, measure the microclimates within those structures, and determine the timing of immergence and emergence and the length of the hibernation season. We radiotracked 10 little brown bats to underground hibernacula dispersed along two ridge systems. All hibernacula were ≤ 24.2 km from where the bats were captured. Eight bats hibernated in the "Milieu Souterrain Superficiel" (MSS), a network of air-filled underground voids between the rock fragments found in scree (talus) deposits. Two bats hibernated in holes in the soil beneath the root system of a tree or stump (rootball). At least two hibernacula in the MSS were reused in subsequent years. Average MSS and rootball temperatures were warmer and more stable than ambient temperature and were well below the optimal growth range of the fungus that causes WNS. Temperatures in the MSS dropped below freezing, but MSS temperatures increased with depth, indicating bats could avoid subfreezing temperatures by moving deeper into the MSS. Relative humidity (RH) approached 100% in the MSS and under rootballs and was more stable than ambient RH, which also was high, but dropped substantially during periods of extreme cold. Acoustic monitoring revealed that bats hibernated by late October and began emerging by the second week of April; estimates of minimum length of the hibernation season ranged from 156 to 190 days. The cold temperatures, dispersed nature of the hibernacula, and close proximity of hibernacula to summering areas may slow the spread and reduce the impacts of WNS on local populations of little brown bats.

Hepatic lipid signatures of little brown bats (Myotis lucifugus) and big brown bats (Eptesicus fuscus) at early stages of white-nose syndrome

White-nose syndrome (WNS) is an emergent wildlife fungal disease of cave-dwelling, hibernating bats that has led to unprecedented mortalities throughout North America. A primary factor in WNS-associated bat mortality includes increased arousals from torpor and premature fat depletion during winter months. Details of species and sex-specific changes in lipid metabolism during WNS are poorly understood and may play an important role in the pathophysiology of the disease. Given the likely role of fat metabolism in WNS and the fact that the liver plays a crucial role in fatty acid distribution and lipid storage, we assessed hepatic lipid signatures of little brown bats (Myotis lucifugus) and big brown bats (Eptesicus fuscus) at an early stage of infection with the etiological agent, Pseudogymnoascus destructans (Pd). Differences in lipid profiles were detected at the species and sex level in the sham-inoculated treatment, most strikingly in higher hepatic triacylglyceride (TG) levels in E. fuscus females compared to males. Interestingly, several dominant TGs (storage lipids) decreased dramatically after Pd infection in both female M. lucifugus and E. fuscus. Increases in hepatic glycerophospholipid (structural lipid) levels were only observed in M. lucifugus, including two phosphatidylcholines (PC [32:1], PC [42:6]) and one phosphatidylglycerol (PG [34:1]). These results suggest that even at early stages of WNS, changes in hepatic lipid mobilization may occur and be species and sex specific. As pre-hibernation lipid reserves may aid in bat persistence and survival during WNS, these early perturbations to lipid metabolism could have important implications for management responses that aid in pre-hibernation fat storage.

Hibernacula microclimate and declines in overwintering bats during an outbreak of white-nose syndrome near the northern range limit of infection in North America

We document white-nose syndrome (WNS), a lethal disease of bats caused by the fungus Pseudogymnoascus destructans (Pd), and hibernacula microclimate in New Brunswick, Canada. Our study area represents a more northern region than is common for hibernacula microclimate investigations, providing insight as to how WNS may impact bats at higher latitudes. To determine the impact of the March 2011 arrival of Pd in New Brunswick and the role of hibernacula microclimate on overwintering bat mortality, we surveyed bat numbers at hibernacula twice a year from 2009 to 2015. We also collected data from iButton temperature loggers deployed at all sites and data from HOBO temperature and humidity loggers at three sites. Bat species found in New Brunswick hibernacula include Myotis lucifugus (Little Brown Bat) and M. septentrionalis (Northern Long-eared Bat), with small numbers of Perimyotis subflavus (Tricolored Bat). All known hibernacula in the province were Pd-positive with WNS-positive bats by winter 2013. A 99% decrease in the overwintering bat population in New Brunswick was observed between 2011 and 2015. We did not observe P. subflavus during surveys 2013-2015 and the species appears to be extirpated from these sites. Bats did not appear to choose hibernacula based on winter temperatures, but dark zone (zone where no light penetrates) winter temperatures did not differ among our study sites. Winter dark zone temperatures were warmer and less variable than entrance or above ground temperatures. We observed visible Pd growth on hibernating bats in New Brunswick during early winter surveys (November), even though hibernacula temperatures were colder than optimum for in vitro Pd growth. This suggests that cold hibernacula temperatures encountered near the apparent northern range limit for Pd do not sufficiently slow fungal growth to prevent the onset of WNS and associated bat mortality over the winter.

Ecology and impacts of white-nose syndrome on bats

The recent introduction of Pseudogymnoascus destructans (the fungal pathogen that causes white-nose syndrome in bats) from Eurasia to North America has resulted in the collapse of North American bat populations and restructured species communities. The long evolutionary history between P. destructans and bats in Eurasia makes understanding host life history essential to uncovering the ecology of P. destructans. In this Review, we combine information on pathogen and host biology to understand the patterns of P. destructans spread, seasonal transmission ecology, the pathogenesis of white-nose syndrome and the cross-scale impact from individual hosts to ecosystems. Collectively, this research highlights how early pathogen detection and quantification of host impacts has accelerated the understanding of this newly emerging infectious disease.

Continued preference for suboptimal habitat reduces bat survival with white-nose syndrome

Habitat alteration can influence suitability, creating ecological traps where habitat preference and fitness are mismatched. Despite their importance, ecological traps are notoriously difficult to identify and their impact on host–pathogen dynamics remains largely unexplored. Here we assess individual bat survival and habitat preferences in the midwestern United States before, during, and after the invasion of the fungal pathogen that causes white-nose syndrome. Despite strong selection pressures, most hosts continued to select habitats where disease severity was highest and survival was lowest, causing continued population declines. However, some individuals used refugia where survival was higher. Over time, a higher proportion of the total population used refugia than before pathogen arrival. Our results demonstrate that host preferences for habitats with high disease-induced mortality can create ecological traps that threaten populations, even in the presence of accessible refugia.

Temperature-dependent host–pathogen interactions may lead species to shift their thermal preferences under pathogen pressure. However, here the authors show that bats have not altered their microclimate preferences due to temperature-mediated mortality from white-nose syndrome, finding instead a sustained preference for warmer sites with high mortality.

Body mass and hibernation microclimate may predict bat susceptibility to white-nose syndrome

In multihost disease systems, differences in mortality between species may reflect variation in host physiology, morphology, and behavior. In systems where the pathogen can persist in the environment, microclimate conditions, and the adaptation of the host to these conditions, may also impact mortality. White-nose syndrome (WNS) is an emerging disease of hibernating bats caused by an environmentally persistent fungus, Pseudogymnoascus destructans. We assessed the effects of body mass, torpid metabolic rate, evaporative water loss, and hibernaculum temperature and water vapor deficit on predicted overwinter survival of bats infected by P. destructans. We used a hibernation energetics model in an individual-based model framework to predict the probability of survival of nine bat species at eight sampling sites across North America. The model predicts time until fat exhaustion as a function of species-specific host characteristics, hibernaculum microclimate, and fungal growth. We fit a linear model to determine relationships with each variable and predicted survival and semipartial correlation coefficients to determine the major drivers in variation in bat survival. We found host body mass and hibernaculum water vapor deficit explained over half of the variation in survival with WNS across species. As previous work on the interplay between host and pathogen physiology and the environment has focused on species with narrow microclimate preferences, our view on this relationship is limited. Our results highlight some key predictors of interspecific survival among western bat species and provide a framework to assess impacts of WNS as the fungus continues to spread into western North America.

Genome-Wide Changes in Genetic Diversity in a Population of Myotis lucifugus Affected by White-Nose Syndrome

Novel pathogens can cause massive declines in populations, and even extirpation of hosts. But disease can also act as a selective pressure on survivors, driving the evolution of resistance or tolerance. Bat white-nose syndrome (WNS) is a rapidly spreading wildlife disease in North America. The fungus causing the disease invades skin tissues of hibernating bats, resulting in disruption of hibernation behavior, premature energy depletion, and subsequent death. We used whole-genome sequencing to investigate changes in allele frequencies within a population of Myotis lucifugus in eastern North America to search for genetic resistance to WNS. Our results show low F_ST values within the population across time, i.e., prior to WNS (Pre-WNS) compared to the population that has survived WNS (Post-WNS). However, when dividing the population with a geographical cut-off between the states of Pennsylvania and New York, a sharp increase in values on scaffold GL429776 is evident in the Post-WNS samples. Genes present in the diverged area are associated with thermoregulation and promotion of brown fat production. Thus, although WNS may not have subjected the entire M. lucifugus population to selective pressure, it may have selected for specific alleles in Pennsylvania through decreased gene flow within the population. However, the persistence of remnant sub-populations in the aftermath of WNS is likely due to multiple factors in bat life history.

Numerous cold arousals and rare arousal cascades as a hibernation strategy in European Myotis bats

Hibernating bats optimise the duration of torpor bouts and arousals in relation to hibernaculum microclimatic conditions and fat reserves. Clustering has significant physiological and ecological benefits, promoting successful hibernation of individuals. Such aggregations may help maintain optimal temperatures, allowing better energy utilisation than in solitarily bats. However, aroused bats in a cluster could conceivably disturb those still hibernating, starting an energy-demanding arousal process. Our study was conducted over two winters in two different hibernacula (cave and mine) in the Czech Republic, where Greater mouse-eared bats (Myotis myotis) have previously been diagnosed with white-nose syndrome. In 118 arousal episodes we recorded 193 individual arousals in which a warming phase was observed, 135 (69.9%) being cold arousals, where bats ceased increasing their body temperatures at ≤ 10 °C. The remaining arousals were standard normothermic arousals, where body (fur) surface temperatures reached > 20 °C. Cold arousals occurred during the mid- and late hibernation periods, suggesting they were a response to disturbance by a neighbour in the same cluster. Arousal cascades, where bats aroused in series, were rare (12.7%) and reached a maximum in mid-January. Our data suggest that Myotis bats prolong their torpor bouts using numerous cold arousals but few arousal cascades. Upon arrival of a bat, the clustered bats show tolerance to disturbing by conspecifics.

Hibernation temperature-dependent Pseudogymnoascus destructans infection intensity in Palearctic bats

White-nose syndrome (WNS) is a fungal disease caused by Pseudogymnoascus destructans that is devastating to Nearctic bat populations but tolerated by Palearctic bats. Temperature is a factor known to be important for fungal growth and bat choice of hibernation. Here we investigated the effect of temperature on the pathogenic fungal growth in the wild across the Palearctic. We modelled body surface temperature of bats with respect to fungal infection intensity and disease severity and were able to relate this to the mean annual surface temperature at the site. Bats that hibernated at lower temperatures had less fungal growth and fewer skin lesions on their wings. Contrary to expectation derived from laboratory P. destructans culture experiments, natural infection intensity peaked between 5 and 6°C and decreased at warmer hibernating temperature. We made predictive maps based on bat species distributions, temperature and infection intensity and disease severity data to determine not only where P. destructans will be found but also where the infection will be invasive to bats across the Palearctic. Together these data highlight the mechanistic model of the interplay between environmental and biological factors, which determine progression in a wildlife disease.

White-nose syndrome detected in bats over an extensive area of Russia

Background

Spatiotemporal distribution patterns are important infectious disease epidemiological characteristics that improve our understanding of wild animal population health. The skin infection caused by the fungus Pseudogymnoascus destructans emerged as a panzootic disease in bats of the northern hemisphere. However, the infection status of bats over an extensive geographic area of the Russian Federation has remained understudied.

Results

We examined bats at the geographic limits of bat hibernation in the Palearctic temperate zone and found bats with white-nose syndrome (WNS) on the European slopes of the Ural Mountains through the Western Siberian Plain, Central Siberia and on to the Far East. We identified the diagnostic symptoms of WNS based on histopathology in the Northern Ural region at 11° (about 1200 km) higher latitude than the current northern limit in the Nearctic. While body surface temperature differed between regions, bats at all study sites hibernated in very cold conditions averaging 3.6 °C. Each region also differed in P. destructans fungal load and the number of UV fluorescent skin lesions indicating skin damage intensity. Myotis bombinus, M. gracilis and Murina hilgendorfi were newly confirmed with histopathological symptoms of WNS. Prevalence of UV-documented WNS ranged between 16 and 76% in species of relevant sample size.

Conclusions

To conclude, the bat pathogen P. destructans is widely present in Russian hibernacula but infection remains at low intensity, despite the high exposure rate.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1521-1) contains supplementary material, which is available to authorized users.

Growth medium and incubation temperature alter the Pseudogymnoascus destructans transcriptome: implications in identifying virulence factors

Pseudogymnoascus destructans is the causal agent of bat white-nose syndrome (WNS), which is devastating some North American bat populations. Previous transcriptome studies provided insight regarding the molecular mechanisms involved in WNS; however, it is unclear how different environmental parameters could influence pathogenicity. This information could be useful in developing management strategies to mitigate the negative impacts of P. destructans on bats. We cultured three P. destructans isolates from Atlantic Canada on two growth media (potato dextrose agar and Sabouraud dextrose agar) that differ in their nitrogen source, and at two separate incubation temperatures (4 C and 15 C) that approximate the temperature range of bat hibernacula during the winter and a temperature within its optimal mycelial growth range. We conducted RNA sequencing to determine transcript levels in each sample and performed differential gene expression (DGE) analyses to test the influence of growth medium and incubation temperature on gene expression. We also compared our in vitro results with previous RNA-sequencing data sets generated from P. destructans growing on the wings of a susceptible host, Myotis lucifugus. Our findings point to a critical role for substrate and incubation temperature in influencing the P. destructans transcriptome. DGE analyses suggested that growth medium plays a larger role than temperature in determining P. destructans gene expression and that although the psychrophilic fungus responds to different nitrogen sources, it may have evolved for continued growth at a broad range of low temperatures. Further, our data suggest that down-regulation of the RNA-interference pathway and increased fatty acid metabolism are involved in the P. destructans-bat interaction. Finally, we speculate that to reduce the activation of host defense responses, P. destructans minimizes changes in the expression of genes encoding secreted proteins during bat colonization.

BATS RECOVERING FROM WHITE-NOSE SYNDROME ELEVATE METABOLIC RATE DURING WING HEALING IN SPRING

Host responses to infection with novel pathogens are costly and require trade-offs among physiologic systems. One such pathogen is the fungus Pseudogymnoascus destructans (Pd) that causes white-nose syndrome (WNS) and has led to mass mortality of hibernating bats in eastern North America. Although infection with Pd does not always result in death, we hypothesized that bats that survive infection suffer significant consequences that negatively impact the ability of females to reproduce. To understand the physiologic consequences of surviving infection with Pd, we assessed differences in wing damage, mass-specific resting metabolic rate, and reproductive rate between little brown myotis ( Myotis lucifugus) that survived a winter in captivity after inoculation with Pd (WNS survivors) and comparable, uninfected bats. Survivors of WNS had significantly more damaged wing tissue and displayed elevated mass-specific metabolic rates compared with Pd-uninfected bats after emergence from hibernation. The WNS survivors and Pd-uninfected bats did not significantly differ in their reproductive capacity, at least in captivity. However, our metabolic data demonstrated greater energetic costs during spring in WNS survivors compared with uninfected bats, which may have led to other consequences for postpartum fitness. We suggest that, after surviving the energetic constraints of winter, temperate hibernating bats infected with Pd faced a second energetic bottleneck after emerging from hibernation.

Determinants of Pseudogymnoascus destructans within bat hibernacula: implications for surveillance and management of white-nose syndrome

1. Fungal diseases are an emerging global problem affecting human health, food security and biodiversity. Ability of many fungal pathogens to persist within environmental reservoirs can increase extinction risks for host species and presents challenges for disease control. Understanding factors that regulate pathogen spread and persistence in these reservoirs is critical for effective disease management. 2. White-nose syndrome (WNS) is a disease of hibernating bats caused by Pseudogymnoascus destructans (Pd), a fungus that establishes persistent environmental reservoirs within bat hibernacula, which contribute to seasonal disease transmission dynamics in bats. However, host and environmental factors influencing distribution of Pd within these reservoirs are unknown. 3. We used model selection on longitudinally collected field data to test multiple hypotheses describing presence-absence and abundance of Pd in environmental substrates and on bats within hibernacula at different stages of WNS. 4. First detection of Pd in the environment lagged up to one year after first detection on bats within that hibernaculum. Once detected, the probability of detecting Pd within environmental samples from a hibernaculum increased over time and was higher in sediment compared to wall surfaces. Temperature had marginal effects on the distribution of Pd. For bats, prevalence and abundance of Pd were highest on Myotis lucifugus and on bats with visible signs of WNS. 5. Synthesis and applications. Our results indicate that distribution of Pseudogymnoascus destructans (Pd) within a hibernaculum is driven primarily by bats with delayed establishment of environmental reservoirs. Thus, collection of samples from Myotis lucifugus, or from sediment if bats cannot be sampled, should be prioritized to improve detection probabilities for Pd surveillance. Long-term persistence of Pd in sediment suggests that disease management for white-nose syndrome should address risks of sustained transmission from environmental reservoirs.

Body temperatures of hibernating little brown bats reveal pronounced behavioural activity during deep torpor and suggest a fever response during white-nose syndrome

Hibernating animals use torpor [reduced body temperature (T _b) and metabolic rate] to reduce energy expenditure during winter. Periodic arousals to normal T _b are energetically expensive, so hibernators trade off arousal benefits against energetic costs. This is especially important for bats with white-nose syndrome (WNS), a fungal disease causing increased arousal frequency. Little brown bats (Myotis lucifugus) with WNS show upregulation of endogenous pyrogens and sickness behaviour. Therefore, we hypothesized that WNS should cause a fever response characterized by elevated T _b. Hibernators could also accrue some benefits of arousals with minimal T _b increase, thus avoiding full arousal costs. We compared skin temperature (T _sk) of captive Myotis lucifugus inoculated with the WNS-causing fungus to T _sk of sham-inoculated controls. Infected bats re-warmed to higher T _sk during arousals which is consistent with a fever response. Torpid T _sk did not differ. During what we term "cold arousals", bats exhibited movement following T _sk increases of only 2.2 ± 0.3 °C, compared to >20 °C increases during normal arousals. Cold arousals occurred in both infected and control bats, suggesting they are not a pathophysiological consequence of WNS. Fever responses are energetically costly and could exacerbate energy limitation and premature fat depletion for bats with WNS. Cold arousals could represent an energy-saving mechanism for both healthy and WNS-affected bats when complete arousals are unnecessary or too costly. A few cold arousals were observed mid-hibernation, typically in response to disturbances. Cold arousals may, therefore, represent a voluntary restriction of arousal temperature instead of loss of thermoregulatory control.

Energy conserving thermoregulatory patterns and lower disease severity in a bat resistant to the impacts of white-nose syndrome

The devastating bat fungal disease, white-nose syndrome (WNS), does not appear to affect all species equally. To experimentally determine susceptibility differences between species, we exposed hibernating naïve little brown myotis (Myotis lucifugus) and big brown bats (Eptesicus fuscus) to the fungus that causes WNS, Pseudogymnoascus destructans (Pd). After hibernating under identical conditions, Pd lesions were significantly more prevalent and more severe in little brown myotis. This species difference in pathology correlates with susceptibility to WNS in the wild and suggests that survival is related to different host physiological responses. We observed another fungal infection, associated with neutrophilic inflammation, that was equally present in all bats. This suggests that both species are capable of generating a response to cold tolerant fungi and that Pd may have evolved mechanisms for evading host responses that are effective in at least some bat species. These host-pathogen interactions are likely mediated not just by host physiological responses, but also by host behavior. Pd-exposed big brown bats, the less affected species, spent more time in torpor than did control animals, while little brown myotis did not exhibit this change. This differential thermoregulatory response to Pd infection by big brown bat hosts may allow for a more effective (or less pathological) immune response to tissue invasion.

Balancing the Costs of Wildlife Research with the Benefits of Understanding a Panzootic Disease, White-Nose Syndrome

Additional ethical issues surrounding wildlife research compared with biomedical research include consideration of the harm of research to the ecosystem as a whole and the benefits of conservation to the same species of animals under study. Research on white-nose syndrome in bats provides a case study to apply these considerations to determine whether research that harms ecosystems under crisis is justified. By expanding well-established guidelines for animal and human subjects research, we demonstrate that this research can be considered highly justified. Studies must minimize the amount of harm to the ecosystem while maximizing the knowledge gained. However, the likelihood of direct application of the results of the research for conservation should not necessarily take priority over other considerations, particularly when the entire context of the ecologic disaster is poorly understood. Since the emergence of white-nose syndrome, researchers have made great strides in understanding this panzootic disease and are now in a position to utilize this knowledge to mitigate this wildlife crisis.

White-nose syndrome survivors do not exhibit frequent arousals associated with Pseudogymnoascus destructans infection

BACKGROUND

White-nose syndrome (WNS) has devastated bat populations in North America, with millions of bats dead. WNS is associated with physiological changes in hibernating bats, leading to increased arousals from hibernation and premature consumption of fat reserves. However, there is evidence of surviving populations of little brown myotis (Myotis lucifugus) close to where the fungus was first detected nearly ten years ago.

RESULTS

We examined the hibernation patterns of a surviving population of little brown myotis and compared them to patterns in populations before the arrival of WNS and populations at the peak of WNS mortality. Despite infection with Pseudogymnoascus destructans, the causative fungal agent, the remnant population displayed less frequent arousals from torpor and lower torpid body temperatures than bats that died from WNS during the peak of mortality. The hibernation patterns of the remnant population resembled pre-WNS patterns with some modifications.

CONCLUSIONS

These data show that remnant populations of little brown myotis do not experience the increase in periodic arousals from hibernation typified by bats dying from WNS, despite the presence of the fungal pathogen on their skin. These patterns may reflect the use of colder hibernacula microclimates by WNS survivors, and/or may reflect differences in how these bats respond to the disease.

Sex and hibernaculum temperature predict survivorship in white-nose syndrome affected little brown myotis (Myotis lucifugus)

White-nose syndrome (WNS), an emerging infectious disease caused by the novel fungus Pseudogymnoascus destructans, has devastated North American bat populations since its discovery in 2006. The little brown myotis, Myotis lucifugus, has been especially affected. The goal of this 2-year captive study was to determine the impact of hibernacula temperature and sex on WNS survivorship in little brown myotis that displayed visible fungal infection when collected from affected hibernacula. In study 1, we found that WNS-affected male bats had increased survival over females and that bats housed at a colder temperature survived longer than those housed at warmer temperatures. In study 2, we found that WNS-affected bats housed at a colder temperature fared worse than unaffected bats. Our results demonstrate that WNS mortality varies among individuals, and that colder hibernacula are more favourable for survival. They also suggest that female bats may be more negatively affected by WNS than male bats, which has important implications for the long-term survival of the little brown myotis in eastern North America.