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

Abstract

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.

Capture Rate Declines of Northern Myotis in the Canadian Maritimes

“…First, the capture data used only consisted of one year of post‐WNS monitoring, which introduces uncertainties into our analyses regarding long‐term trends. However, because capture trends in all 3 provinces were comparable to one another and hibernacula surveys (Vanderwolf and McAlpine 2021), the drastic post‐WNS changes in capture rates and ratios we found are almost certainly attributable to Pd rather than a short‐term event unique to 2019. Second, capture data was collated from independent studies with different research objectives, meaning the trap and net placement was not identical across pre‐ and post‐WNS sampling.…”

Biomarker Metabolites Discriminate between Physiological States of Field, Cave and White-nose Syndrome Diseased Bats

“…2 KRI-v = Kovats Retention Index for specific volatile metabolite represented by the individual peak and retention time for a 10 m DB-5 column using 11-alkane (C7-C17) analytical reference-standard calibration. 3 CAS number = Chemical Abstracts Service (CAS) Registry Number, unique numerical identifier. 4 KRI-t = Kovats Retention Index for tentative identify for compounds; indicated as most probable identity based on closest KRI-values.…”

“…2 Biomarker number (in numerical order by retention times). 3 Retention times (to 0.01 s) for biomarker VOCs present in minor-peak, whole-body emissions detected with a 10 m DB-5 column using GC-analysis parameters specified previously. 4 Peak areas are represented as ranges of areas (under each chromatogram peak curve) for the given number of bats (indicated in parentheses).…”

“…White-nose syndrome (WNS), a necrotrophic fungal disease found primarily in cave-dwelling Nearctic bats, has reduced bat populations in some eastern regions of North America by as much as 99% [ 1 , 2 , 3 ]. WNS is caused by a keratinophilic fungal pathogen, Pseudogymnoascus destructans (Pd), that develops epidermal and deep, subcutaneous skin infections in at least twelve insectivorous bat species [ 4 , 5 ].…”

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

“…Most experimental infection trials on WNS have been conducted with little brown bats ( Myotis lucifugus ) 8 , 9 , 15 , 30 – 33 and there is a recognized need to study the interactions among host, pathogen, and environmental conditions in other bat species whose populations are declining from WNS 12 . In natural habitats, P. subflavus hibernate across a range of environmental conditions, including at temperatures associated with high Pd growth rates and high disease mortality 22 , 24 , 26 , 29 , 34 .…”