Reindeer have no internal body
clock, according to scientists.
Researchers found that the animals
are missing a “circadian clock” that influences processes including
the sleep-wake cycle and metabolism.
This enables them to better cope
with the extreme Arctic seasons of polar day, when the sun stays up all day,
and polar night, when it does not rise.
The team from the universities of
Manchester and Tromso report their study in Current Biology journal.
The body clock, or circadian clock,
is the internal mechanism that drives hormone release on a rhythmic 24-hour
Light also influences these
hormonal rhythms, but in most mammals, this “circuit” also involves
the circadian clock, which can influence the release of hormones without the influence
Anyone who has experienced jet lag
is familiar with the effect of the body clock.
But the research team from research
institutes in the UK and Norway found that, in Arctic reindeer, this circadian
clock was absent.
Professor Andrew Loudon from The
University of Manchester took part in the study.
He said that the reindeer may have
“abandoned use of the daily clock that drives biological rhythms” in
order to survive the extreme conditions in the Arctic.
He and his colleagues studied
reindeer living in Northern Norway, 500 km north of the Arctic Circle. Here
there are 15 weeks of continuous daylight in summer and eight weeks during the
winter where the Sun does not appear over the horizon.
They investigated levels of the
hormone called melatonin – which is important in the sleep-wake cycle – in the
They found that there was no
natural internal rhythm of melatonin release into the blood – the hormone
simply responded to the cycle of light and dark.