Svalbard ptarmigan’s internal clock ticks all year round
The Svalbard ptarmigan (Lagopus muta hyperborea) is the only terrestrial bird species to live year-round in the High Arctic, made possible by its perfect adaptation to environmental conditions that vary extremely throughout the year. Even during periods of constant light conditions, i.e. polar day or polar night, the ptarmigan’s internal clock continues to run and “reminds” it, for example, of breeding business as Norwegian researchers have found in a new study.
The daily routine of many plants and animals follows a circadian rhythm according to the length of the day, which causes the organisms to perform certain activities at certain times of the day. In addition, it also influences certain body functions in animals and humans (sleep-wake rhythm, heart rate, body temperature, etc.). This rhythm is regulated by an external timer such as light.
But what effects do constant light conditions over a longer period of time have on the animals living there, as they naturally prevail in the Arctic midsummer?
Scientists at the Arctic University of Norway in Tromsø investigated this question and studied the behaviour of Svalbard ptarmigan and the activation of various genes under different light conditions over a period of 12 weeks. They observed that as the length of daylight increased to 24 hours of brightness, the ptarmigan’s activities became more and more distributed throughout the day and could no longer be assigned to a consistent pattern, in contrast to ptarmigans that were exposed to six hours of daylight within 24 hours and essentially restricted their activities to this time. Animals that received a longer light pulse (4 h) at the same time every day as well as a shorter light pulse (2 h) which was shifted backwards week by week, also showed activity only in the light phases.
Based on these observations, Daniel Appenroth and his colleagues investigated the key genes that are active for the establishment of 24-hour rhythms in the ptarmigan brain. They found that the ptarmigan’s circadian clock even temporally controls seasonal activities such as breeding. In birds exposed to daylight around the clock, the researchers demonstrated that genes related to reproduction were activated. In addition, the animals increased their activity in preparation for mating.
The experiments lead scientists to assume that the birds’ internal clock “checks” 14 hours after sunrise to see if the sun is still up.
Julia Hager, PolarJournal
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