Jun 25 2013
Last Friday the solstice set our annual biological clocks. Every day the sun triggers our circadian rhythm. But what if we lived where the sun never sets? How would we synchronize our daily internal clocks?
In the arctic where day and night last for months a circadian rhythm would be annoying if not a handicap. Since “day” has no meaning, arctic reindeer solved the problem by turning off their internal 24-hour clocks.
In mammals the circadian rhythm causes melatonin levels to rise at night and fall during the day. This happens whether or not the sun gives us a cue.
Scientists studying reindeer in Norway (Rangifer tarandus, the same species as caribou) found that they have no rhythmic melatonin cycle. Instead their melatonin rises or falls abruptly in response to light. On or off. No daily clock.
Reindeer need to know the time of year so they can synchronize migration and breeding, but this is easy to do at the equinox when the sun rises and sets.
On Svalbard where this reindeer lives, the sun rose on April 16 and won’t set until August 27.
No wonder he doesn’t care what time it is. Some days I wish I didn’t care either.
Read more about this study in Science Daily, March 2010.
(photo of a Svalbard reindeer, a subspecies of Rangifer tarandus, from Wikimedia Commons. Click on the image to see the original)