WNS Research

Kunz Lab WNS Research Projects

Death by Starvation: An Hypothesis-Based Approach for Addressing White-Nose Syndrome in Hibernating Bats

deadbats

Dead bats in the snow at the base of a tree outside Aeolus Cave, VT. Bats at affected sites are often seen flying outside in mid-winter when it is unlikely they will find any insects to eat. Photo: Jon Reichard.

Summary: We propose that a reduction in the quantity and quality of insects during the pre-hibernation period in autumn may limit the deposition of adequate stores of white adipose tissue (WAT) and thus compromise successful hibernation, and ultimately reproductive success. WAT is the primary source of energy that sustains bats (and other hibernators) throughout the winter when they have no access to food. Moreover, because insectivorous bats cannot synthesize polyunsaturated fatty acids (PUFAs), deficiencies in dietary PUFAs during the pre-hibernation period in autumn may reduce the duration and depth of torpor during hibernation. Frequent arousals may result in premature depletion of WAT before the end of the hibernation period. Depleted WAT at this time also may contribute to a decrease in leptin production (necessary for ovulation and successful reproduction by females), or, in the worst cases, the inability to arouse from torpor or inability to mount an immune response to possible pathogens.
We are analyzing body composition and dietary composition (including PUFAs) of bats little brown myotis (Myotis lucifugus) during the pre-hibernation period at sites both affected by and unaffected by WNS to test five hypotheses that may help reveal or rule out causes of premature deaths or compromised reproductive success in these hibernating bats. Destructive body composition analysis provides the most accurate and reliable estimates of total body water, WAT, and lean dry mass, and analyses of PUFAs in WAT collected from bats, stomach contents, and insects during the pre-hibernation fattening period.

Are Hibernating Bats Affected with ‘White Nose Syndrome’ Immunocompromised?

Summary: To help identify the potential causes and correlates of White Nose Syndrome (WNS) in North American hibernating bat species, we are assessing various aspects of relative immune function in free-ranging populations. Multiple methods are being used to measure different arms of the immune system in bats from affected and unaffected sites. Additionally, a time course of blood samples has been collected from torpid bats and bats that have incrementally higher body temperatures, or stages of arousal. These approaches test several hypotheses associated with WNS. First, measuring relative immune function in bats from affected and unaffected sites will help elucidate whether or not bats with WNS are experiencing immunosuppression. If they are, this study will identify if reduced immune defenses are solely due to physiological constraints associated with deep torpor or due to some other cause, such as an immunosuppressive infectious agent, a contaminant, or a lack of sufficient energy reserves. Second, measuring immune function in bats at different stages of arousal will specifically test the ability of hibernating bats, in general, to mount an immune response. Based on research in other hibernating mammals, it is possible that bats must arouse from torpor to mount an effective immune response, and in support of this hypothesis, preliminary analysis of a timed blood collection series that we performed in February 2008 suggests that as bats arouse from torpor, their ability to kill Escherichia coli increases. Results from our preliminary study, in the winter of 2008, also suggests that there may be a statistically significant difference in immune function between bats with visible signs of fungal infections and those without. Moreover, it is possible that WNS-affected bats are both immunocompromised due to an extrinsic factor or factors as well as constraints associated with the physiology of torpor.

Wing Damage Caused by White-Nose Syndrome Extends Threats to Bats Beyond Hibernation into Active Summer Months

damaged-wings

Severe scarring and necrosis on the wing of a little brown myotis. Photo: Laura Le.

Summary: In this study, we are assessing scarring and necrosis on wings of WNS-affected bats. Damaged wings may have lasting consequences for reproductive success and survival throughout the active season. We developed a 4-point wing damage index (WDI = 0 to 3) to assess the incidence and severity of wing damage in the months following emergence from hibernation. Overall, reproductive rate was 85.1% in 2008; slightly lower than in previous studies. Severe wing damage was observed until 4 June and moderate damage was observed through 9 July. Body mass index was lowest for bats with severe wing damage. Thus, wing damage appears to affect foraging success and may hinder predator avoidance of little brown myotis. The timing, incidence, and geographic range of wing damage to little brown myotis observed in 2008 correspond to those of WNS at hibernacula. Monitoring wing conditions of affected and healthy bats will be important for monitoring the spread of the syndrome and establishing baseline data for unaffected wings. The simple scale we propose should be useful for monitoring wing conditions in any bat population. The objective of continuing studies is to determine the effect of wing damage on flight performance.

Geographic Distribution of the Psychrophilic Fungus (Geomyces sp.) Associated with White-Nose Syndrome

Summary: This study is designed to document the geographic distribution of the fungus that has been directly associated with WNS, by collecting samples of organic matter—the substrate on which the psychrophylic fungus (Geomyces sp.) is known to colonize—and using geographic information systems (GIS) to evaluate its distribution with respect to available landscape and environmental variables in the eastern US over a three-year period. This study is designed to test the hypothesis that the fungus associated with WNS is restricted to the northeastern states, as currently known. This is one of the key research needs identified by scientists who participated in a conference on WNS was convened in Albany, New York (June 9-11, 2008), and attended by over 100 research scientists and natural resource managers (Science Strategy Meeting, 2008). Several questions, hypotheses, and research needs were proposed and discussed by this body of participating scientists, including those advanced in this study. The consensus among those in attendance is that knowledge of the geographic distribution of the fungus associated with WNS is critical to understanding its epidemiology.

A Novel BatCam for Censusing Maternity Colonies of Bats in Regions Affected by White-Nose Syndrome

Summary: This project is designed to test impact of winter mortality on the size of selected maternity colonies of little brown myotis (Myotis lucifugus) within the known summer range of hibernating bats affected by WNS. This is one of the key research needs identified by scientists who participated in a conference on WNS that was convened in Albany, New York (June 9-11, 2008), and attended by over 100 research scientists and natural resource managers. Among the questions, hypotheses, and research needs proposed and discussed by this body of participating scientists, knowledge of the size and overall health of summer colonies is important for assessing the impact of WNS on bats in the northeastern U.S. We developed a BatCam that will be installed at selected maternity roosts with access to reliable electricity and Internet services. In the event that Internet services are not accessible, we will collect data on a laptop and download census data weekly for analysis. The BatCam is a digital video camera modified to capture infrared light. With this device we will record nightly emergence and returning activity of bats to assess colony sizes and foraging times. BatCam data may be used to estimate seasonal fluctuations in maternity colony size.

Are Bats Affected by White-Nose Syndrome Unable to Arouse when they are Disturbed during Hibernation?

Summary: During visits to hibernacula for body condition and immunological studies (above) we recorded time-lapse infrared thermal images of clusters of hibernating bats. Bats are expected to arouse from torpor when they are disturbed by researchers entering the cave or mine, but it has been hypothesized that WNS-affected bats lack the energy stores (fat) to do so. We measured two clusters for 2.5 to 4 hours during each visit to affected sites. Clusters are being analyzed for warming rates of individual bats and the proportion of bats in the cluster that arouse after ‘disturbance.’ If WNS-affected bats are unable to arouse, we expect to see little change in bat temperatures in response to our presence in the hibernaculum. Bats may also exhibit brief euthermic periods and re-enter torpor without relocating in the cave or mine. This study may also reveal the relative number of bats in these clusters that are euthermic regardless of disturbance.