Ask the Experts: Does ketosis occur during hibernation?

We received this interesting question from a reader regarding a previous post about the role of evaporative water loss in bats afflicted with white nose syndrome (WNS):

"Are bats during hibernation in ketosis? I suspect that normally they are not, that fatty acids are used to generate enough heat to keep warm, and the glycerine from the lipid is used for gluconeogenesis.

If they had insulin resistance, and needed more glucose or ketone bodies to supply tissue compartments that couldn't sustain themselves on fatty acids and had to incude ketosis, that could explain the starvation (ketosis is not as efficient of calories as is simple oxidation).

The appearance of fungus outside the nose is curious. It almost seems as if the fungus is obtaining nutrients from the exhaled air of the bat, like volatile ketones if the bat was in ketosis."

We sent this question to Dr. Craig Willis, an expert on bat hibernation and White Nose Syndrome. Here is his response:

"Interesting idea and neat comment. We don't know if bats are in ketosis during hibernation and the question highlights one of the big challenges for studying WNS: We know very little about hibernation energetics in bats. It seems likely that, like ground squirrels, bats in torpor may rely on ketones to fuel metabolism to some extent, especially in the brain. They may also rely more and more on this as fat reserves run out and they start to show signs of starvation. However our hunch is that it's unlikely infection with G. destructans (which causes WNS) affects this process beyond ketosis occurring as a sign of starvation.

In terms of the fungus benefiting from exhaled ketones around the nose, it's important to keep in mind that the fungus doesn't just grow on the nose. White-nose syndrome is a catchy but sort of unfortunate name. The most consistent clinical sign of WNS is infection of the wings with G. destructans. Yes, exposed skin of the nose (and ears) is also invaded by the fungus but it's the wings that really seem to be taking the hit. The fungus digests and erodes the epidermis, blood vessels, glands of the skin (etc), although it doesn't invade other organs. So the fungus grows very well on and in wings and ears and obtain its nutrients from skin. Also important, so far, the organs of bats with WNS don't appear to be badly affected (the fungus doesn't invade other organs). If the fungus was causing changes to metabolic pathways or insulin responses one might expect to see something going on in liver or pancreas, for example but, so far, there doesn't seem to be evidence of that.

So - in summary, the short answer is we don't know. But the available evidence doesn't suggest to us that ketosis is a major part of the disease.

It is a heartbreaking conservation challenge in any case so we appreciate your interest."

Stay tuned for more updates on this devastating disease.

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