Arctic reindeer abandon use of internal clock to survive in extreme cold

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Washington, March 12 (ANI): A new study has shown that Arctic reindeer have abandoned use of the internal clock that drives the daily biological rhythms in other organisms, in order to live under extreme conditions in the Arctic.

"Our findings imply that evolution has come up with a means of switching off the cellular clockwork," said Andrew Loudon of the University of Manchester.

"Such daily clocks may be positively a hindrance in environments where there is no reliable light-dark cycle for much of the year," he added.

Light-dark cycles drive hormone rhythms via a circuit that involves the eye and nervous system projections to structures involved in regulating hormone rhythms, in particular melatonin, Loudon explained.

In most mammals, this wiring circuit also involves an internal clock that drives hormone levels in a rhythmic 24-hour fashion, even when there is no light-dark cycle.

"In reindeer, it is this clock element that seems to be missing," Loudon said.

The reindeer show no natural internal rhythm of melatonin secretion at all. Instead, hormone levels rise and fall in direct response to light and dark.

The researchers show that melatonin levels remain at or below detectable levels during daylight hours.

Those hormone concentrations spike almost as soon as the light goes out, only to dive again when it switches back on.

Further studies by Loudon and his colleague Karl-Arne Stokkan of the University of Tromsx in Norway using reindeer skin cells showed that two well-known clock genes don't oscillate the way they do in other organisms as a way of keeping time.

"We suspect that they have the full range of normal clock genes, but these are regulated in a different way in reindeer," Loudon said.

According to the researchers, the findings initially came as a surprise, but they now suspect that similar patterns will be uncovered in other Arctic animals. (ANI)

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