White nose syndrome, continued

Image Source: Smithsonian Institution

As mentioned in previous posts, white nose syndrome is responsible for the decimation of hibernating North American bats. The cause of death is starvation attributed to increased arousal when the bats should be hibernating.

Dr. Craig K.R. Willis and colleagues have published new findings supporting the plausibility of " the dehydration hypothesis", that infections on the wing membranes of bats leads to dehydration thereby increasing the frequency of arousals. They found that the rate of evaporative water loss (EWL) was higher for a species that is most susceptible to WNS, little brown bats (Myotis lucifugus), compared to a species for which WNS has a much lower mortality rate, Natterer's bats (Myotis nattereri). Under both dry air (panel A) and humid air (panel B) conditions, the Natterer's bats had lower levels of EWL compared to the little brown bats. The findings are depicted in figure 3 from the paper:


Some of the data are predicted from the literature. But the author's findings suggest that another trigger for early arousal may be to help maintain water balance. Clearly more research into the nature of WNS should be conducted to help eradicate this deadly fungus.

CKR Willis, AK Menzies, JG Boyles, MS Wojciechowski. Evaporative water loss is a plausible explanation for mortality of bats from White-nose syndrome. Integrative and Comparative Biology 51(3): 364-373, 2011.

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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.

Could the fungus be dependent upon the increased CO2 level at the bat's nose? Would scrubbing the CO2 out of the air of a bat cave in any way help the unfortunate creatures by slightly lowering the CO2 levels in their exhalations and thus around their noses? The level of carbon dioxide in their exhaled breath when they are active is undoubtedly much higher than ambient atmospheric levels, but maybe the fungus could be disrupted enough to help the bats when they are hybernating, when the level of CO2 from their breath is probably much lower.

It would be interesting to know exactly what pH and what bicarbonate level is optimal for the fungus to thrive.