A recent discovery has shown that the common shore dwelling ragworms Nereis virens and Nereis diversicolor, normally associated more with angling than with high profile science, have a biological clock which is able to track not just the passage of the days and tides but can also probably tell the time of one without the presence of the other. Confused? Kim Last, a SAMS research scientist who is leading the investigation together with scientists from the Universities of Newcastle and Leicester explains why the humble ragworm is such an interesting animal when it comes to clock biology:
“The timing of virtually all behavioural and physiological functions in terrestrial organisms is orchestrated by the daily, or circadian, molecular clock which runs with a periodicity of ~24 hours. Marine organisms, however, such as the ragworms, live in an environment in which they are additionally exposed to tidal cycles with an average periodicity 12.4 hours.
Collecting ragworms from a muddy estuary in Northumberland.
Dr Last continues:
"Being a worm you are wise to avoid both daytime predators such as birds, and tidal predators such as fish, and hence you need an accurate clock to tell you both the time of day and tide. When we studied ragworms in the laboratory we found that the majority of animals preferred to come out of their burrows to search for food at night, just as the tide was beginning to flood, which is probably the safest time to be “out on the town”!
However when the lights and tides were removed, the worms continued to show daily/tidal predictive emergence behaviour which demonstrated that this complex clock was innate i.e. they were not just responding to the environmental cues.
The Worm monitor
The activity of worms is monitored using artificial worm burrows (c) in the bottom of aquaria (a) which are guarded by infra-red switches (b) which work much like automatically opening doors.
Perhaps most interestingly some animals (Nereis diversicolor in particular) have displayed a phenomenon we have coined “cross-modal entrainment” or CME. CME is where animals maintained under daily cycles display a tidal activity pattern even though there are no tides (this also works visa versa). Consequently the circadian component of Nereis’s biological clock must be able to “communicate” with the tidal component, a sort of inbuilt nautical tide table for worms, the function of which is still a mystery."
Through this research we are gradually gaining insights into the workings of our own circadian clock which probably evolved from a more complex solar/lunar chronometer at a time when we were little more than worms ourselves many millions of years ago”.
These findings have recently been published: Last, K. S., Bailhache, T., Kramer, C., Kyriacou, C. P., Rosato, E., Olive, P. J. W. (2009). Tidal, daily, and lunar-day activity cycles in the marine polychaete Nereis virens. Chronobiology International, 26: 2, 167-183.