Observed Resiliency of Little Brown Myotis to Long-Term White-Nose Syndrome Exposure

Abstract

White-nose syndrome (WNS) is a disease that has killed millions of bats in eastern North America and has steadily been spreading across the continent. Little brown myotis Myotis lucifugus populations have experienced extensive declines; however, some localized populations have remained resilient, with bats surviving multiple years past initial WNS exposure. These persistent populations may be critical to species recovery, and understanding mechanisms leading to this long-term survival and persistence may provide insight into overall bat and disease management. We monitored a maternity colony of little brown myotis on Fort Drum Military Installation in northern New York between 2006 and 2017 to determine basic demographic parameters and find evidence of what may be leading to resiliency and persistence at this site. Total colony size declined by approximately 88% from 2008 to 2010 due primarily to impacts of WNS. Counts of all adults returning to the colony stabilized during 2010–2014 (mean = 94, range 84–101) and increased after 2014 (mean = 132, range = 108–166). We captured 727 little brown myotis (575 females, 152 males) and banded 534 individuals (389 females, 145 males) at the colony. The majority of sampled bats showed evidence of recent past WNS infection and exposure to Pseudogymnoascus destructans, and we documented pervasive presence and limited viability of the fungus within the colony's main roosting structure. We recaptured 98 individually marked females in years after initial banding, and some individuals survived at least 6 y. Ninety-one percent of all adult females, 93% of recaptured bats, and 90% of 1-y-old females (i.e., bats recaptured the first year after initial capture as juveniles) showed evidence of reproduction during the monitoring period. Using mark–recapture models, we estimated annual survival rates of juvenile and adult little brown myotis during 2009–2016 and examined whether reproductive condition or evidence of recent infection of WNS had any effect on survival. Annual survival rates were similar between juveniles and adults, but highly variable, ranging from 41.0 to 86.5%. Models indicated that neither evidence of recent past exposure to WNS nor reproductive status were related to survival. No one parameter stood out as being responsible for this colony's continued existence, and it is likely that many interwoven factors were responsible for the observed resilience. Although relatively high reproductive effort from all females (i.e., both1-y-old and >1-y-old ) and intermittently suitable survival rates have led to the continued persistence of, and population increases in, this summer colony, mortality from WNS and inherently low reproductive potential still seemed to be limiting population growth. Until there is a better understanding of this overall potential resiliency in little brown myotis, we recommend considering minimizing disturbance and direct human involvement within these persisting populations to allow whatever natural recovery that may be occurring to evolve uninterrupted.

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

“…The microclimate, habitat type, and physical features of White Cave are similar to other known hibernacula in the region and do not appear uniquely favorable for successful hibernation. Other studies have documented multiyear survival of bats post‐WNS, together with evidence of reproduction in the USA (Dobony & Johnson, 2018; Frick et al., 2017; Reichard et al., 2014). Additional monitoring will be necessary to ascertain if long‐term survival and reproduction is occurring among bat species that overwinter in New Brunswick post‐WNS.…”

Resistance is futile: RNA-sequencing reveals differing responses to bat fungal pathogen in Nearctic Myotis lucifugus and Palearctic Myotis myotis

“…The inflammatory responses, occurring only during arousals Field et al (2018), maybe maladaptive, and the immunopathology related to infection could be a major driver of mortality associated with WNS, at least in M. lucifugus (Lilley et al 2017). Recent reports have described populations of M. lucifugus in northeastern North America that are beginning to stabilize at substantially reduced population sizes, or even showing signs of population increase since the initial mass mortality following the arrival of WNS (Langwig et al 2017; Dobony and Johnson 2018). This has led to speculation that this could be due to strong selection for those individual bats that responded to P. destructans with tolerance rather than a detrimental overresponse to fungal infection (Frick et al 2017).…”

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

“…The initial impacts of WNS on six species of hibernating bats in the northeastern and midwestern USA have varied from almost complete extirpation to arrested population growth at the colony scale (Turner et al 2011), leading to extensive declines at larger geographic scales (Thogmartin et al 2012;Ingersoll et al 2013). After the initial decline caused by WNS in M. lucifugus, reports have surfaced describing stabilization of colonies at smaller sizes or even increases in numbers of individuals in some areas (Langwig et al 2015;Frick et al 2017;Dobony and Johnson 2018). Models parameterized with long-term data on fungal loads, infection intensity and counts of M. lucifugus at hibernacula have suggested development of either tolerance or resistance in these persisting populations (Frick et al 2017).…”