The softshell clam (Mya arenaria), which occurs along the Atlantic coast of North America, is a commercially important bivalve with a wide distribution. Particular species of dinoflagellates (such as Alexandrium), sometimes referred to as red tide, bloom off the Maine and Canadian coast starting in early spring and throughout the summer. These dinflagellates produce paralytic shellfish toxins (PSTs), which in high concentrations, are capable of blocking nerve function, leading to paralysis. While these toxins typically aren’t present in threatening concentrations, Mya arenaria can collect them in their body tissue at higher concentrations via filter feeding the toxic algae.
Paralytic shellfish poisoning (PSP) in humans results from the ingestion of shellfish which have been recently feeding on the toxic algae. This resulting PSP constitutes a large public health hazard and is the cause for severe economic losses in the shellfish industry on both coasts of North America.
The Connell Lab has discovered a mutation in the gene responsible for the voltage gated sodium channel in certain populations of softshell clams. This mutation allows for a greatly increased resistance to PSTs and is found most often in clam populations residing in an area with a history of red tide blooms. While this resistance protects the clams against paralysis, it also allows them to continue feeding during a bloom of toxic algae which leads to a much higher biomagnification of the toxin. This directly affects the shellfish industry as it can increase the severity of possible poisoning and force us to close clam beds for a longer period of time. We are currently undergoing further investigation on the scale of this mutation in the wild and the dynamics of resistance development. Currently we are tracking survival and growth of both sensitive and resistant bred clams as a means of understanding how quickly a clam population would shift towards resistance following the onset of regular blooms of toxic algae.
Check out our Clam Mutations Photo Gallery:
Clam mutations considered one of the "15 Evolutionary Gems" in 2009 editorial by the journal Nature.
- Bricelj, V M, S MacQuarrie, J A E Doane and L B Connell (2010)."Evidence
of selection for resistance to paralytic shellfish toxins duringthe
early life history of softshell clam, Myaarenaria, populations."
Limnology and Oceanography 55:
2463-2475. doi:10.4319/lo.2010.55.6.2463 [VIEW PDF]
- Connell, L B (2009). "Selective pressure of paralytic shellfish toxins on populations of softshell clam, Mya arenaria." MDIBL Bulletin 48: 121-122.
- Connell, L B and S A Hamilton (2008). "Determination of a naturally occurring sodium channel gene mutation in eastern Maine populations of softshell clam, Mya arenaria." The Bulletin Mount Desert Island Marine Biological Laboratory 47:136-137.
- Scott Hamilton and Laurie Connell (2009) Improved methodology for tracking and genetically identifying the softshell clam, Mya arenaria. Journal of Shellfish Research, Vol. 28, No. 4, 747–750.
- Phillips, J, L B Connell and V M Bricelj (2011).Sodium channel variant
in the softshell clam Mya arenaria offers natural resistance to toxic
algal blooms. Proceedingsof the 14th International Meeting on Harmful
Algae. Hersonissos, Greece: In
Connell and Scott Hamilton (2007) Determination of a naturally
occurring sodium channel gene mutation in eastern Maine populations of
softshell clam, Mya arenaria. MDIBL Bulletin. 2007
LB, MacQuarrie SP, Twarog BM, Iszard M, Bricelj VM (2006) Population
differences in nerve resistance to paralytic shellfish toxins in
softshell clam, Mya arenaria, associated with sodium channel mutations. Marine Biology .
V. M., L. B. Connell, et al. (2005). Sodium channel mutation leading to
saxitoxin resistance in clams increases risk of PSP. Nature. 434:
763-767. [VIEW PDF]
- Connell, L. B., B. M. Twarog, et al. (2004). Development of resistance to paralytic shellfish toxins in the softshell clam, Mya arenaria,
via a single mutation in the sodium channel pore region: II. Molecular
identification of a mutation associated with the resistant phenotype in
multiple populations, Cape Town South Africa.
- Trainer, V. L., K. Konoki, et al. (2004). Development of resistance to paralytic shellfish toxins in the softshell clam, Mya arenaria, via a single mutation in the sodium channel pore region: III. Electrophysiological studies, Cape Town South Africa.
L. B., V. L. Trainer, et al. (2002). A molecular basis for variation in
resistance to paralytic shellfish toxins in bivalve molluscs. Tenth
International Conference on Harmful Algal Blooms, St Pete Beach FL.
- Connell, L. B., V. M. Bricelj, et al. (2000). Cloning and identification of a sodium channel gene from the clam Mya arenaria. Symposium on Harmful Marine Algae in the US, Woods Hole MA, USA, Woods Hole MBL.
Project funded by:
NOAAs ECOHAB Research Program