Biological clocks defy circadian rhythms

Abstract

Some marine invertebrates have at least two internal clocks, which follow different times and have different mechanisms, according to two new studies. Multiple timepieces might prove common among animals. The two marine organisms investigated show biological rhythms that are influenced by the Moon, as well as possessing the more familiar circadian clock that follows the daily cycle of sunlight and dark. The circadian and non-circadian rhythms work in parallel and use different molecular mechanisms, and in one of the cases, a monthly 'lunar' clock could modulate the daily clock. All this suggests that there is much left to discover about how time is kept inside more complex organisms, including humans. "This is the first molecular evidence that the clocks aren't the same," says Chris Chabot, a biologist at Plymouth State University in New Hampshire who was not involved in either of the new studies. Life rhythms Circadian rhythms are synchronized to the 24-hour day and are found in every kingdom of life. They are well understood, thanks to work in model organisms such as the fruitfly Drosophila and the mouse. But the mechanisms underlying non-circadian rhythms are not so well understood, largely because of a lack of accessible organisms that have distinct rhythms and can also be experimentally manipulated. A non-circadian rhythm well known to biologists is the 'circatidal' rhythm (in time with the tides), which repeats every 12.4 hours. This is found in coastal species such as the speckled sea louse (Eurydice pulchra, see image below), which is the subject of a study published today in Current Biology 1. The bristle worm Platynereis dumerilii has a biological clock that follows lunar phases, which is ruled by a separate mechanism than the circadian clock that is synchronised with the Sun.