Reduced immune responsiveness contributes to winter energy conservation in an Arctic bird

Animals in seasonal environments must prudently manage energy
expenditure to survive the winter. This may be achieved through
reductions in the allocation of energy for various purposes (e.g.
thermoregulation, locomotion, etc.). We studied whether such tradeoffs
also include suppression of the innate immune response, by
subjecting captive male Svalbard ptarmigan (Lagopus muta
hyperborea) to bacterial lipopolysaccharide (LPS) during exposure
to either mild temperature (0°C) or cold snaps (acute exposure to
−20°C), in constant winter darkness when birds were in energyconserving
mode, and in constant daylight in spring. The innate
immune response was mostly unaffected by temperature. However,
energy expenditure was below baseline when birds were immune
challenged in winter, but significantly above baseline in spring. This
suggests that the energetic component of the innate immune
response was reduced in winter, possibly contributing to energy
conservation. Immunological parameters decreased (agglutination,
lysis, bacteriostatic capacity) or did not change (haptoglobin/PIT54)
after the challenge, and behavioural modifications (anorexia, mass
loss) were lengthy (9 days). While we did not study the mechanisms
explaining these weak, or slow, responses, it is tempting to speculate
they may reflect the consequences of having evolved in an
environment where pathogen transmission rate is presumably low
for most of the year. This is an important consideration if climate
change and increased exploitation of the Arctic would alter pathogen
communities at a pace outwith counter-adaption in wildlife.