Partridge sacrificed immunity for the sake of survival in the Arctic winter

Researchers from Sweden and Norway found that the tundra ptarmigan from the Arctic archipelago of Svalbard in the winter time spend to fight infections less energy than in the spring. This allows you to keep more resources to maintain body temperature. As noted by the authors in their article in the journal Journal of Experimental Biology, this strategy may seem risky, but it seems to work well in high latitudes, where pathogenic microorganisms and viruses inactive for most of the year.

In the cold period of the year the animals faced with food shortage, forcing many of them to migrate or drastically reduce the level of metabolism. However, some birds and mammals not only overwinter in high latitudes, but remain active. To survive difficult times, they must intelligently manage energy resources, primarily using them for keeping warm and cutting down expenditures on other functions of the body.

The immune system uses a lot of energy, so it is not surprising that animals have to compromise between its work and the maintenance of body temperature. As a result, the intensity of immune reactions in the cold season in many species of warm-blooded decreases. It is unclear what exactly is the reason for seasonal changes of immune system — temperature, length of daylight or the condition of the body.

Swedish and Norwegian scientists under the leadership of Andreas Nord (Andreas Nord) from the Lund University analyzed the balance between the immune system and thermal regulation on the example of the Spitsbergen subspecies of the tundra ptarmigan (Lagopus muta hyperborea), inhabiting the eponymous archipelago and Franz Joseph. It is the only bird, wintering so far North, making it an ideal object for such studies. Through the winter the partridges help insulating plumage, fat reserves and decrease in motor activity.

The researchers conducted experiments with 12 adult males, six of which were born in captivity and six were caught on the Svalbard at the age of one to three weeks. In cages, where they lived partridges are kept for the duration of daylight, similar to the Svalbard. In winter, the birds contained in the complete darkness at a temperature of zero degrees Celsius, introduced the lipopolysaccharide of Escherichia coli (Escherichia coli) — non-pathogenic antigen that triggers the innate immune response, which manifests itself in the form of fever.

After that partridges we measured body temperature, metabolic rate at rest and the level of biomarkers of the immune response. In addition, within three weeks after infection recorded the appetite of the birds and changes in the mass of their body. The experiment was then repeated under different conditions: in winter in the dark and after a drop in temperature to minus 20 degrees Celsius, and a spring under continuous light and temperatures of zero degrees Celsius and minus 20 degrees Celsius.

It turned out that the partridges which were subjected to the false security of winter, metabolic rate was on average four percent below the baseline level. At the same time, the spring injection of bacterial lipopolysaccharide increased the level of metabolism in the average of nine percent. This suggests that in winter, the birds prefer to spend less energy to fight infection.

Biomarkers of immune responses also behaved unusually. The level of most of them decreased in ten hours after infection and then either grew slowly or remained at a low level. Based on these data, the body of partridges consumed all existing immune cells and very slowly, we synthesized a new. A long period of refusal to eat and lose weight after “infection”, which averaged 9 days, also indicates the slow elimination of the toxins from the body.

Thus, when the shortage of food in the cold tundra ptarmigan reduced the cost of dealing with infections, not to spend the resources necessary for thermoregulation. This strategy may seem risky, since it increases their vulnerability to infections in the cold season. However, the authors suggest that such a compromise is justified in the far North, where diversity and speed of transmission of pathogens is small for most of the year. Unfortunately, rapid climate change and Arctic people can accelerate the spread of infections and to put the existence of amazing birds at risk.

With the harsh winter conditions faced not only birds but also small mammals — for example, the common shrew (Sorex araneus). These insectivorous active at low temperatures and thus do not carry stock. The winter body mass and brain volume in shrews decrease, which should lead to the acceleration of metabolism. However, for some strange reason this is not happening.

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