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Is the Little Brown Bat's Immune System Adapting to White-nose Syndrome?

A cluster of little brown bats in a cave in Vermont

Director's Choice
A Minute with the Scientist

Deahn Donner: While a lot of people were focusing on the front edge of the disease and the fungus, we were focusing more on the backside of the infection line, and also the front section of the line. Let's start looking at those that have been infected with the fungus for a while, and a population that hasn't been infected yet with the fungus and white nose syndrome. And so, the Midwest at the time, did not have white nose syndrome. And so, we replaced space for time, and we looked at our pre-white nose syndrome population against the post-white nose syndrome infection of the East, and saying, let's look at their adaptive resistance. And so, that's sort of what we put together, and we realized when we did this, that it was going to take more than just Paula and I, and we knew that Dan had a lot of experience with the fungus.

Dan Lindner: You know, most of our genome is set, and it's designed to be able to come up with a system that can respond to new threats. And, there are so many aspects of that, from where immunity first starts in terms of our skin barriers, or how the mucus in our air tract works, and to the particular immune cells that a pathogen might first be interacting with, then this immune cascade has so many different branches, so many different parts.

Deahn Donner: The difficult part is that it changes and it adapts, but that's exactly why we wanted to look at it. So, in and of itself, we were taking on a very complicated topic, and to do that, you can't do it one discipline, you can't do it in one place. It really does take so many experts from a wide variety of disciplines to bring the whole picture back. And that includes our field biologists, our managers, researchers, wildlife, geneticists, big data, immune systems. It really took a lot.

Dan Lindner: What we really want is we want information for management. How can you better manage this disease? How can you better help these populations? And, if you can understand how the bats are adapting, and is it through the microbes on their skin or is it truly genetic, then that can really feed into these different management approaches.

Deahn Donner: Yeah, if we can understand what's going on at the individual level, then we can scale that up to populations, and then individual hibernaculums, and then multiple hibernaculums, and more at the landscape, and let the principles of conservation biology in small isolated populations to then naturally repopulate an area. So, that really depends on understanding all those scales and all that management from the individual response to the fungi on the wing, to all the way where they are on the landscape, to much broader on that and how it's going to spread—and how that recovery can spread as well.

Deahn Donner: I'm a Deahn Donner, I'm a research landscape ecologist with Northern Research Station located in Rhinelander, Wisconsin.

Dan Lindner: And, I'm Daniel Lindner, a research plant pathologist located in Madison, Wisconsin.

A small number of little brown bat populations have persisted in the eastern United States after a decade of exposure to the fungal pathogen responsible for the white-nose syndrome. Could these surviving populations be developing an effective adaptive immune response to the disease?

American hibernating bats have declined rapidly over the last decade due to an invasive fungal pathogen that causes white-nose syndrome (WNS). The fungus erodes the skin of hibernating bats, causing individuals to wake from torpor more frequently, resulting in increased dehydration and lower fat reserves, leading to mortality. Widespread extirpation of the once common little brown bat was predicted, but after a decade of multi-year fungus exposure, small populations in the eastern United States have persisted, leading to the question of whether the bats’ immune response is adapting and helping to counteract the infection. Northern Research Station scientists and their partners compared allelic diversity of an immune gene (specifically, MHC class II DRB) between these persisting populations and naïve populations (pre-WNS) located in Wisconsin and Michigan to test whether WNS produced selection on this immune gene. High allelic admixture between the populations indicated no signal of WNS selection. However, lower allelic richness in the persisting populations indicated effects from genetic bottleneck and drift following rapid population declines, suggesting stochastic forces are stronger than directional selection for this fungal pathogen. Management activities can help ensure connectivity of these small, persisting populations to help recover allelic diversity and reduce their vulnerability to other stressors and future environmental change.