CBC North – Caribou living in the Arctic have switched off the internal biological clock most mammals use to distinguish day from night, biologists have found. Researchers in the U.K. and Norway say the lack of an internal clock is the caribou’s adaptation to the “land of the midnight sun,” where the sun doesn’t set for months at a time during the summer and doesn’t rise during the winter. “Our findings imply that evolution has come up with a means of switching off the cellular clockwork,” Andrew Loudon of the University of Manchester said in a statement. “Such daily clocks may be positively a hindrance in environments where there is no reliable light-dark cycle for much of the year” … The researchers examined the expression of clock genes in the skin cells of caribou, also called reindeer, but suspect that similar results would be seen in other animals that live in the Arctic.

View abstract: “A Circadian Clock Is Not Required in an Arctic Mammal” (Current Biology, March 11, 2010).

Link to source

More information:

• Science Daily: “To Arctic Animals, Time of Day Really Doesn’t Matter” (March 11, 2010).
• BBC: “Reindeer body clock switched off” (March 15, 2010).