Upper Midwest Environmental Sciences Center
Principal Investigator: Wayne Thogmartin
White-nose syndrome (WNS), a novel fungal pathogen of cave-hibernating bat species in east and central North America, is causing the most precipitous decline in bat populations ever reported. This disease causes mortality in at least 6 species of bats, including the endangered Indiana Bat (Myotis sodalis), with mortality rates in some hibernacula averaging 95%. Since the onset of this disease in winter 2006, approximately 6 million bats are estimated to have been killed. The disease was also recently found in another endangered bat, the Gray Bat (Myotis griscescens), though mortality of this species due to white nose syndrome has not been documented as of spring 2012.
Fungal invasions, many of which are pathogenic, are an emerging global threat. Thirty-eight (38) fungal species are currently spreading in the United States, causing diseases ranging from Dutch elm blight to skin infections and severe mortality in amphibians. Fungal pathogens are also increasingly recognized as a serious threat to food security.
The fungal pathogen associated with white-nose syndrome (Geomyces destructans) is a previously undescribed psychrophilic (cold-loving) and keratinophilic (hair- and skin-associated) fungus. Species of Geomyces are ubiquitous, found in soils of temperate and high-latitude ecosystems and capable of withstanding and thriving in cold, low-nutrient polar environments, as well as in various marine ecosystems. Species in this genus are dispersed by wind, groundwater, other animals, and humans on their clothing and equipment. The white-nose syndrome-causing species, G. destructans, is believed to have originated in Europe, but no unusual mortality is known in hibernating bat species occurring there (sensitive species there may have been extirpated millennia ago). G. destructans is known to persist in caves in North America and Europe even in the absence of bats.
The immune response of bats is depressed when in hibernation, making them especially susceptible to disease during winter. White-nose syndrome is characterized by a cutaneous (skin) infection appearing as a white, filamentous or powdery growth on the nose, ears and wing membranes; emaciation; atypical behavior causing bats to emerge prematurely from hibernacula in mid-winter; and ulcerated, necrotic and scarred wing membranes in bats recently emerged from hibernation.
Because novel pathogens are capable of causing extinction of naïve species, we initiated a model-based study of risk faced by the endangered Indiana bat to white-nose syndrome. The Indiana bat is of concern due to its status as endangered under the U.S. Endangered Species Act of 1973, as amended (16 U.S.C. 1531 et seq.); it is also a red-listed species according to the International Union for the Conservation of Nature. In our study, we developed a computer simulated population model to forecast future population dynamics of the endangered Indiana bat subject to white-nose syndrome. Our population model incorporated environmental and population factors and their associated variability to predict the probability of extinction.
Using observed rates of disease spread (9-19%), we estimated >90% of current wintering populations are predicted to experience white-nose syndrome within the next 20 years. This could cause the proportion of populations existing at the extinction threshold (250 female bats) to increase by 34% over 50 years. When bat populations are projected to be lowest (year 2022), we predicted 14% of the initial total population to remain, totaling ~29,000 females. By 2022, only 12 of the initial 52 wintering populations were predicted to possess the breeding females necessary to sustain their populations.
If the species can develop immunity to the disease, we predict ~4% of wintering populations to be above the 250-female threshold after 50 years (year 2057), following a 69% decline in total abundance (from 211,000 to 65,000 females). At the bottom of these projections (year 2022), we predict regional near-extirpation of wintering populations in 2 of 4 bat regions (Ozark-Central and Appalachians), while in a third region (Midwest), where the species is currently most abundant, >95% of wintering populations are predicted to fall below 250 females. If robust growth in the Northeastern population prior to onset of white-nose syndrome was not aided by immigration from the other 3 regions, then the Northeastern population may regain pre-white-nose syndrome population sizes after several decades. If, on the other hand, growth is fueled by immigration from other regions, our projections of population response might be unduly optimistic.
Emerging information on the spread of white-nose syndrome among wintering populations suggests that our predictions relating to the timing of extirpation may be somewhat conservative. Research by others suggests increasing abundance in this endangered species prior to the disease was likely aided by a warming climate; projections of future climate, however, suggest increasing constraints to summer breeding habitat due to warming. We are continuing and expanding our study of risk posed by Indiana bats. As part of a national assessment of impacts of wind energy development on wildlife, we are investigating potential consequences of wind energy on mortality of migrating and breeding Indiana and Little Brown bats (Myotis lucifugus, the species most affected by white-nose syndrome). Our goal is to refine our estimates of species risk resulting from synergistic effects of multiple stressors (wind energy development, white-nose syndrome, and land use change). This information will help U.S. Fish and Wildlife Service in endangered species listing considerations.
White-nose syndrome affects bats at their most sensitive life history stage, during winter hibernation. Model results suggest white-nose syndrome is capable of causing severe reductions in total population size as well as local and regional extinction of the Indiana bat. Impacts of other stressors not yet studied could further complicate long-term viability of the species.
For details, see:
Thogmartin, W. E., C. Sanders-Reed, J. A. Szymanski, R. A. King, L. Pruitt, P. C. McKann, M. C. Runge, and R. E. Russell. 2013. White-nose syndrome is likely to extirpate the endangered Indiana bat over large parts of its range. Biological Conservation 160:162–172.
Szymanski, J. A., L. Pruitt, M. C. Runge, M. Armstrong , R. A. King, C. McGowan, R. Niver, D. Sparks, and D. C. Brewer. 2010. Developing performance criteria for a population model for Indiana Bat conservation. A case study from the structured decision making workshop, December 8–12, 2008, National Conservation Training Center, Shepherdstown, West Virginia, USA.
Thogmartin, W. E., R. A. King, J. A Szymanski, and L. Pruitt. 2012. Space-time models for a panzootic in bats, with a focus on the endangered Indiana bat. Journal of Wildlife Diseases 48:876–887.
Thogmartin, W. E., P. C. McKann, R. A. King, J. A. Szymanski, and L. Pruitt. 2012. Population-level impact of white-nose syndrome on the endangered Indiana bat. Journal of Mammalogy 93:1086–1098.