Bats save energy by reducing energetically costly immune functions
during annual migration

Date:
October 15, 2020
Source:
Forschungsverbund Berlin
Summary:
A team of scientists led by the Leibniz Institute for Zoo and
Wildlife Research (Leibniz-IZW) investigated whether and how the
immune response changes between pre-migration and migration seasons
in the Nathusius pipistrelle bat. They confirmed that migratory
bats favour the energetically ''cheaper'' non-cellular (humoral)
immunity during an immune challenge and selectively suppress
cellular immune responses.

Thereby, bats save energy much needed for their annual migration.



FULL STORY ==========================================================================
Both seasonal migration and the maintenance and use of an effective
immune system come with substantial metabolic costs and are responsible
for high levels of oxidative stress. How do animals cope in a situation
when energy is limited and both costly body functions are needed? A team
of scientists led by the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) investigated whether and how the immune response changes
between pre-migration and migration seasons in the Nathusius pipistrelle
bat. They confirmed that migratory bats favour the energetically "cheaper" non-cellular (humoral) immunity during an immune challenge and selectively suppress cellular immune responses. Thereby, bats save energy much needed
for their annual migration. The results are published in the scientific
journal Scientific Reports.


==========================================================================
The team of scientists around Christian C. Voigt, head of the Department
of Evolutionary Ecology of the Leibniz-IZW, and Ga'bor A'. Czirja'k,
senior scientist at the Department of Wildlife Diseases of the
Leibniz-IZW, assessed the activity of several branches of the immune
system of the Nathusius pipistrelle bat before and during migration. The seasonal journey of a 7 g Nathusius pipistrelle is energy-intensive since
they fly more than 2,000 km during their annual journeys between the
Baltic countries and southern France, and the metabolic turnover during
flying is an order of magnitude higher than the basal metabolic rate
. "It seems likely that bats will have to trade some body functions such
as the immune response against the high cost of flight during migration,"
Voigt says. In order to verify this conjecture and to elucidate how the
immune system is configured during this pivotal time of the year, the
team measured the cellular and humoral response of the innate immune
system (relative neutrophil numbers and haptoglobin concentration, respectively) and the cellular response of adaptive immunity (relative lymphocyte numbers) before and during migration. They compared baseline
levels of these immune parameters and studied them in response to an
antigen challenge.

"Our results confirm significant differences between the two periods. We conclude that this species of bat pays attention to the energy
requirements of the different branches of immunity when switching from pre-migratory to the migratory season," Voigt explains. Before migration
the cellular response of the innate immune response was significantly
higher than during migration, whereas the humoral response of the same
immune branch was dominant during the migration period. "The Nathusius pipistrelle responds with a strong humoral immune response to a challenge mimicking a bacterial infection. This response is more pronounced during migration, while there is no activation of the cellular response in
such a situation," adds Czirja'k. When the animals embark on their
strenuous journeys they reduce the cellular immune response, which is
more energy-demanding than the humoral response. With this strategy the Nathusius pipistrelle might save energy during migration.

"The open question is whether or not the focus on humoral immunity during
the migration period puts bats at some risk," Voigt says. "It is possible
that they are more susceptible to certain pathogens while migrating if
bats cannot mount an adequate cellular immune response." These and other related questions are now the topic of further immunological research
by the bat research group at the Leibniz-IZW.


========================================================================== Story Source: Materials provided by Forschungsverbund_Berlin. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Christian C. Voigt, Marcus Fritze, Oliver Lindecke, David
Costantini,
Gunārs Pētersons, Ga'bor A'. Czirja'k. The
immune response of bats differs between pre-migration and
migration seasons. Scientific Reports, 2020; 10 (1) DOI:
10.1038/s41598-020-74473-3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201015111719.htm

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