European hibernating bats cope with white-nose syndrome which kills
North American bats

Date:
February 3, 2021
Source:
Leibniz Institute for Zoo and Wildlife Research (IZW)
Summary:
Fungal diseases are a major threat to wildlife, sometimes resulting
in significant population declines or even causing the extirpation
of populations or species. White-nose syndrome, caused by the
cold-loving fungus Pseudogymnoascus destructans, has become a
major cause of death for millions of hibernating bats in North
America. European bats survive when infected by the same fungus
during hibernation.



FULL STORY ==========================================================================
What are the reasons for such a contrast in outcomes? A scientist team
led by the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW)
has now analysed the humoral innate immune defence of European greater mouse-eared bats to the fungus. In contrast to North American bats,
European bats have sufficient baseline levels of key immune parameters and
thus tolerate a certain level of infection throughout hibernation. The
results are published in the journal Developmental and Comparative
Immunology.


========================================================================== During infections caused by Pseudogymnoascus destructans (Pd), North
American bats arouse frequently from hibernation to trigger a more
elaborate immune response, whereas European bats remain dormant, owing,
as the new results reveal, to their competent baseline immunity. Not
being able to deal with the fungus by baseline immunity causes North
American bats to deplete fat stores before the end of winter bnecause
of the need for additional and energetically expensive arousals, which ultimately leads to their starvation. European bats may also arouse once
in a while when infected but their strong baseline immunity allows them
to balance the tight energy budget better during winter hibernation.

For this investigation, the scientists went to hibernation sites in
Germany and studied 61 mouse-eared bats (Myotis myotis) with varying
levels of natural infections by Pseudogymnoascus destructans. The animals
were divided into three groups according to the severity of fungal
infections (asymptomatic, mild symptoms, severe infection). Body mass
and skeletal body size of bats was measured and blood samples taken from
torpid animals. In addition, the team monitored in other conspecifics
how often infected animals arose from hibernation. "We could show that
there is no link between infection and the frequency of waking up from hibernation in the European greater mouse-eared bat," say Marcus Fritze
and Christian C. Voigt, bat experts from the Department Evolutionary
Ecology at Leibniz-IZW. "This is consistent with the idea that the fungus
does not trigger an immune response in European hibernating bats but is
rather kept under control by the bats' baseline immunity." In contrast,
North American bats such as little brown bats (Myotis lucifugus) arouse frequently when infected by the fungus to elicit an immune response.

Frequent arousal and the immune response require energy and prematurely
deplete the body's fat stores before the winter has ended. The protein haptoglobin seems key in the bats' fight against the fungus. Haptoglobin
is an acute phase protein, which can be produced by bats without large metabolic costs. "Our results demonstrated the central role of haptoglobin
in the defence against the fungus. Interestingly, baseline levels of
this protein are sufficient to protect the European host against the
fungus and there is no need to actively synthesise the protein during
the torpid phase," adds Ga'bor A'. Czirja'k, wildlife immunologist at
the Department of Wildlife Diseases of the Leibniz- IZW.

A second key finding of the team's investigation is that heavier European greater mouse-eared bats arouse from hibernation more frequently than
lean conspecifics. This seems counterintuitive because each arousal event causes a depletion of fat stores. Well-nourished bats seem to assist
their immune system by actively clearing off the external fungal hyphens
from their body while being awake for short periods. Thus, heavy bats
are in a healthier condition towards the end of hibernation than lean
animals. Lean animals cannot afford to arouse as often and thus depend on
the efficacy of the baseline immunity to control the fungus. The safety
net of a competent immunity keeps European (and Asian) bats alive during infections with P. destructans but proves to be insufficient for North
American bats.

These results add further evidence that there are differences in the
defence strategies against the causative agent of white-nose syndrome in European and North American bat species. Tolerance strategies aim to limit
the impact of the fungal infection on the health of animals. Resistance strategies, on the other hand, try to actively reduce the load of
pathogens. "Tolerance strategies are effective, as the immune defences of hibernating European mouse-eared bats show," Voigt summarises. "In North American bats, however, this ability is not present to a sufficient
degree, possibly because the Pd fungus originated in Europe, giving
European species a head start in developing efficient defence mechanisms."

========================================================================== Story Source: Materials provided by Leibniz_Institute_for_Zoo_and_Wildlife_Research_(IZW).

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Marcus Fritze, Sebastien J. Puechmaille, David Costantini,
Jo"rns Fickel,
Christian C. Voigt, Ga'bor A'. Czirja'k. Determinants of defence
strategies of a hibernating European bat species towards the fungal
pathogen Pseudogymnoascus destructans. Developmental & Comparative
Immunology, 2021; 119: 104017 DOI: 10.1016/j.dci.2021.104017 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/02/210203123404.htm

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