Molluscan circadian rhythms

Studying intertidal organisms means occasionally escaping from lab and going to the beach! Here I am collecting limpets for the next experiment.
Studying intertidal organisms means occasionally escaping from lab and going to the beach! Here I am collecting limpets for the next experiment.

Rhythms are a dominant aspect of life on Earth. We are subject to the changes between nighttime and daytime, as dictated by Earth’s orbit around the sun. Because this switch happens every single day, our bodies and internal processes have evolved to take full advantage of these changes in environmental conditions while also protecting ourselves from the harshest aspects of night and day. This is why having fully functional biological rhythms, such as the circadian clock, is so important in maintaining optimum health.

We think that, in intertidal organisms, another biological rhythm mechanism exists in addition to the circadian clock: the circatidal clock. The prefix “circa” means around, so these are rhythms with a period that corresponds to the changing of the tides; the commonly accepted definition of a circatidal rhythm is one having a period of 12.4 hours.

The intertidal zone is the interface between land and ocean. In areas that experience two high and two low tides per day, the intertidal zone switches between submergence by the ocean and exposure to the air with a period of approximately 12.4 hours. This translates to a different tide every 6.2 hours. The organisms that live there have this additional rhythm imposed on their lives, in addition to the change between night and day. The changing of the tide presents organisms living in the intertidal zone with highly contrasting environmental conditions, requiring intertidal organisms to adopt different survival strategies throughout the day. As such, we think that intertidal organisms have some sort of internal mechanism, similar to the circadian clock, that allows them to keep track of when they will be submerged or emerged.

Limpets attached to their home scars during low tide. They make their scars to specifically fit their own shells, so that they can create a perfect seal to protect against drying out. If you look closely at the rock, you can see the vacant circular home scars left behind by other limpets.
Limpets attached to their home scars during low tide. They make their scars to specifically fit their own shells, so that they can create a perfect seal to protect against drying out. If you look closely at the rock, you can see the vacant circular home scars left behind by other limpets.

My research focuses on circatidal biological rhythms in intertidal mollusks, specifically oysters, mussels, and limpets. We started out with oysters and mussels to look at rhythmic patterns of gene expression and identified several candidate genes that we think may play a role in the tidal time-keeping mechanism. My current focus is on limpets, because, as gastropod mollusks, they are able to move around, whereas oysters and mussels, which are sessile bivalves, cannot. Every high tide, limpets travel from a fixed location, their home scar, in search of food. This is their only opportunity to feed, so it is important that they time it correctly and do not miss their chance. Because of this, in addition to examining their gene expression rhythms, I can also look at their movement rhythms. By simultaneously looking at gene and movement patterns, I can relate what needs to happen at the molecular level to what needs to happen at the organismal level in order for the animal to successfully track the tide.

Oysters and mussels are both commercially important aquaculture species, as well as being ecologically important ecosystem engineers, providing ecosystem services such as substrate formation and water filtration. Limpets also play an important ecological role, maintaining rock surface algae levels through their grazing. The goal of my research is to enhance understanding of these important intertidal animals, which will ultimately better inform aquaculture and coastal management practices, particularly in the face of the changing global environment.

 

Jacqueline Lin is a PhD Candidate in Marine and Environmental Biology at USC.

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