The genetics and diversity of mussels

PL-Grid computing resources help biologists to understand how mussel species survived the last glaciation

Atlantic mussels are spread equally across European coasts and sea food restaurants. They are also unusual from a genetic point of view: they have mitochondrial DNA from both their fathers and their mothers. Every other organism, from birds to humans, inherits mitochondrial DNA only from the mother’s side.

We would still be running those comparisons if only a single computer could have been used. A. Burzyński

The genetic surprises of mussels don’t stop here: two major studies in the early 1990s have shown that their population is genetically very diverse. Artur Burzyński, a molecular biologist based at the Institute of Oceanology of the Polish Academy of Sciences, and his colleagues were interested in knowing why.

The team looked into what happened to mussels during the last glacial period. This is important because mussels live in coastal areas and their populations were affected by the environmental changes of the glaciations.

For this, they took 985 mitochondrial DNA samples from mussels collected around Europe and analysed the genetic content, looking for polymorphisms, which are distinct features occurring naturally in a species.

Polymorphisms are useful to understand genetic differences in populations: “the more shared polymorphisms between two populations, the more related they are,” explains Burzyński.

Burzyński and the team used parallel computing resources provided by PL-Grid (the Polish national e-Infrastructure) to run their analysis. “The best option was to run the same model several times and compare the results,” he says. “if they are convergent, it is likely the solution is at the global optimum.”

They ran hundreds of serial jobs, each taking a few days. “We would still be running those comparisons if only a single computer could have been used,” he adds.

The team found that all modern mussels coalesced into one single group around 10,000 years ago – at the end of the last glaciation period. And after that, this population underwent rapid expansion genetic diversification.

The results, published in the journal Heredity, suggest that mussel populations survived the last glaciation in a single refugium, most likely located in the north of the Bay of Biscay.

“This relatively quick coalescence of all populations into a single one, coupled with a strong differentiation of the contemporary populations shows how very responsive these mussels are to rapid climate changes,” Burzyński concludes.

Credit: Darkone (Wikimedia Commons)

Reference

Śmietanka et al. 2014. Glacial history of the European marine mussels Mytilus, inferred from distribution of mitochondrial DNA lineages. Heredity doi:10.1038/hdy.2014.23

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