Rudolph, Donner, and Blitzen apparently don't have to worry about jetlag. Unlike most animals and plants, reindeer in the high arctic lose their 24-hour biological clock in summer and winter, according to new research.
Animals, plants, and even fungi have an internal timepiece known as a circadian clock that helps them regulate patterns of activity, growth, and metabolism even in the absence of external cues (ScienceNOW, 31 March:). We'd still get hungry for lunch around noon, for example, even if there were no sun to be seen. But might this clock work differently in the arctic, where day and night can stretch on for months?
To investigate, Karl-Arne Stokkan at the Department of Arctic Biology in Tromso, Norway, and his colleagues attached wristwatch-sized monitors that recorded all movement to six reindeer living in the mountains of northern Norway and six animals of a different subspecies living in the Arctic archipelago of Svalbard, Europe's northernmost territory. Svalbard has day and night for only a few weeks of the year. It is dark from early November through late January, and between April and August the sun never sets.
After a year of collecting data, the researchers found that the Norwegian animals' periods of activity followed a 24-hour pattern during autumn, winter and spring. But during the summer, when the sun doesn't set between late May and mid-July, the animals' activities showed no daily pattern--just an alternation between eating and resting for a few hours at a time, no matter what the clock said. For the animals in the high arctic, the pattern was even more striking: Their movements were independent of any 24-hour clock for most of the year. Only in fall and spring did they show a slight tendency to be more active during the day.
The observations suggest that the reindeer have somehow been able to suppress their circadian clocks, says Stokkan. In the constant light or dark, reindeer are likely better off if they can take advantage of any opportunity to feed rather than remaining on a 24-hour schedule, he says. "Our data suggest the clock is a weak one, and it goes away when it is not needed." But circadian clock researcher Fred Turek at the Northwestern University Institute for Neuroscience in Chicago, Illinois, says that although the lack of rhythm in activity patterns is intriguing, the animals' hormones and body temperature might still be on a 24-hour cycle.
In any case, Stokkan says, the pattern for humans is different. Even in constant dark or constant light, most people seem to run on a roughly 24-hour clock. Early on Christmas morning, he says, "Rudolph can be running like anything, but Santa will get tired."
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