To Arctic animals, time of day really doesn't matter

Mar 11, 2010
Arctic reindeer

In the far northern reaches of the Arctic, day versus night often doesn't mean a whole lot. During parts of the year, the sun does not set; at other times, it's just the opposite. A new study reported online on March 11th in Current Biology shows that Arctic reindeer have come up with a solution to living under those extreme conditions: They've abandoned use of the internal clock that drives the daily biological rhythms in other organisms.

"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."

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 , this wiring circuit also involves an 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 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 Tromsø 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.

The researchers say that the findings initially came as a surprise, but they now suspect that similar patterns will be uncovered in other Arctic animals.

"Synchronization of seasonal cycles in mammals is a prominent feature of physiological adaptation in northern temperate and Arctic species," Loudon and Stokkan write. "Studies of seasonal sheep reveal that melatonin signals need only be present for a few weeks of the year to entrain an annual reproductive cycle. It is attractive to speculate that in reindeer, informative signals associated with equinoxes directly entrain a 'circannual clock' that, at least in reindeer, may not involve circadian mechanisms."

Explore further: Breakthrough in coccidiosis research

More information: Lu et al.: “Report: A Circadian Clock Is Not Required in an Arctic Mammal.” Publishing in Current Biology 20, 1-5, March 23, 2010. DOI:10.1016/j.cub.2010.01.042

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verkle
1 / 5 (3) Mar 11, 2010
It makes me sick to see so many scientists continously ascribe God's design to evolution. There is no scientific proof that "evolution has come up with these means..." so please leave out such ludicrous statements.
Sekhat
5 / 5 (1) Mar 12, 2010
Actually, there is scientific evidence that would suggest that processes within a biological organism would be the result of evolution. However there is -no- scientific proof that there was a god that designed anything. So please leave out such ludicrous statements.
SRDUB2
Mar 12, 2010
This comment has been removed by a moderator.
boldone894
5 / 5 (1) Mar 15, 2010
If science makes you ill, then why are you reading a science news website?
There is virtually no evidence of most things in the bible ever existing outside someone's imagination. There is plenty of evidence that evolution has existed and still occurs.
If you try the argument of "Evolution is only a theory" then please look up "Theory" and "scientific method" before you do so.
There is even evidence of the stories in the bible evolving out of previous stories. Evolution even exists in religion... how about that!