The Tidal Clock Keeping Marine Life Safe

Researchers at the Universities of Aberystwyth and Cambridge have discovered a marine animal that has a tidal clock as well as a body clock
01 October 2013

Interview with 

David Wilcockson, University of Aberystwyth


Scientists have known for a while that probably all living things, us included, have a 24 hour body clock ticking inside them that keeps track of the time so they know when to wake up and when to go to sleep.

But this week, researchers at the Universities of Aberystwyth and Cambridge have discovered a marine animal that also has a tidal clock. As well as the time of day, it can also tell when high tide is due!

David Wilcockson is the senior author on the paper in Current Biology...

David -   Hello, Chris.

Chris -   So, what is this creature?

David -   It's a small crustacean, lives on sandy shores around the UK, and it's called Eurydice pulchra. It's a speckled sea louse. It's only about 5 mm long and it's a marine relative of the wood louse.

Chris -   Why does it need to know when the high tide is coming?

David -   This animal lives buried in the sand when the tide is out.  When the tide comes in, it comes out of the sand to swim.  And so, it needs to know so that it can gear itself up to swim for two or three hours and burry back into the sand before the tide goes out.  And so, it doesn't get stranded in the inappropriate points on the shore.  It stays in its preferred position.

Chris -   So, how did you discover that this organism has this tidal clock?

David -   We've known this for quite some time.  In fact, one of the authors on the paper, Mike Hastings did his PhD on Eurydice way back in the '80s and we know that it has rhythmic behaviour, swimming rhythm with a 12.4-hour or a tidal period.  But what we didn't know is how this 12.4-hour activity was governed, whether it is simply a daily or 24-hour clock that was running a different speed or whether it's a unique tidal clock.  And this is what we've been working on to really uncover how these 12.4-hour rhythms are driven.

Chris -   How have you done that?

David -   So, we've used modern molecular biology as well as some - I think a quite elaborate behaviour of experiments where we manipulate the light regime the animals are exposed to. What we've done is we've sequenced lots of the genes that we know were involved in daily rhythms in other organisms.  We've sequenced those from Eurydice.  One of the things we've done is, we've actually knock down the expression of one of these genes.  That has disrupted daily colour changes in the animal and actually left the 12.4-hour swimming rhythm intact.  So, we've removed the daily clock, but left intact the tidal clock.

Chris -   I see.  So, what you're doing is, you're saying, there are some things that this animal does everyday according to the time of day and that's driven by its normal body clock.  If you dismantle the body clock using various tricks which you've done, then those daily things go away, but it still has this swimming activity every 12 hours, showing it's keeping track of tides in a separate way to the way it keeps track of normal time of day.

David -   That's exactly right.  So, what I just said is, when it's having its 12.4-hour swimming activity, the animals that changes from dark to light on a daily basis with the light dark changes of night and day.  And also, when it's having a high tide at night time, it swims more than it does during a high tide day time.  So, it's a daily modulation of the tidal swimming.  We can actually reduce those by knocking out the daily clock, but we cannot influence, we cannot change the 12.4-hour rhythm of swimming.  So, we've disentangled or disassociated these two clocks.

Chris -   The fact that it's got two different clocks running in its brain, do you think that's unique to this creature or are there many other creatures perhaps even humans included that have other clocks other than our daily body clock?

David -   That's a really important question.  The answer is that, it's definitely not unique to Eurydice.  This is our model organism for non-circadian for tidal rhythms.  But we know that there's many other marine organisms that also have 12.4-hour rhythms of activity and also, lunar rhythms and semi-lunar rhythms of reproduction for example.  There's a paper published at the same time as ours on a small marine worm that has lunar rhythms of reproductive cycles.  They've shown also that they can disentangle a circadian or daily clock and their lunar clocks.  So, they've come up with similar results but in different organism.

Chris -   But you don't yet know what this clock is or how it runs?

David -   Well, that's the next big question really is, what's the nature of this clock and how is it orchestrated, how this 12.4-hour rhythm orchestrated at the molecular and cellular level.  And that's something that we're getting close to having an answer on and we're working on it very hard at the moment.


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