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December 05, 2005— Ottawa, Ontario

Alexandrium, a dinoflagellate algae that produces toxins.

When we hear the term evolution, it's easy to believe that it refers to something in the past, forgetting that nothing stays the same forever. NRC marine bioscience researchers in Halifax, along with partners in the U.S., have pinpointed an important and unexpected molecular change in soft shell clams that greatly increases their resistance to toxins produced by harmful algae blooms in coastal waters known as "Red Tides". The findings of this study were published in Nature.

The discovery is important not only because Canada's shellfish industry is big business, but also because it affects human health. Eating clams or other shellfish that contain large amounts of these toxins impairs the ability of your body to process electrical signals essential to nerve and muscle function, a potentially fatal condition known as Paralytic Shellfish Poisoning. Nerves can't do their job, causing muscle paralysis, because their site of communication, known as the sodium channel, has been blocked by the toxins.

Shellfish stricken by paralytic shellfish poisoning (PSP)

Researchers found that an extremely small change in the DNA, a natural mutation that causes a single amino acid change, greatly decreases the ability of toxins to bind in these channels. Most clams from areas with a history of algal blooms had the mutation and were more resistant than those in regions which have never suffered blooms. The former were able to accumulate toxins much faster, at a rate approximately seven times higher, than the ones which had never previously experienced red tides.

Science at Work for Canada, NRC's 2004-2005 Annual ReportScience at Work for Canada
NRC's 2004-2005 Annual Report

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The discovery is important and unexpected because sodium channel proteins found in the membranes of nerve and muscle fibers have remained virtually unchanged between humans and other more primitive organisms for millennia.

From the point of view of evolution and biology, such a fact is rare and a sign of the extreme importance of sodium channels for nerve response among organisms. In this case, rapid and extreme environmental change (which has caused increased red tides) has now forced rapid evolutionary change.


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National Research Council of Canada
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