

How snails point to the trails of ancient seafarers in Ireland

Cepaea nemoralis, a common land snail, may have been brought over to Ireland when European travelers came over to settle there.

When a group of French or Spanish travelers sailed the Atlantic to Ireland about 8,000 years ago, they carried along a species of snails that today bear genetic witness to their passage. The snails might have been stowaways — or maybe they were just snacks.

Irish land snails today possess certain genetic markers that are shared solely with snails living in the northern Spain and southern France. A single delivery by humans — whether as cargo or escargot — is the best explanation for the genetic relationship between the two geographically distant species, researchers at the University of Nottingham suggest.

"It's a packed lunch that they would have carried around with them," Angus Davison, an evolutionary biologist at the University of Nottingham, told NBC News. His work describing the genetic cousins appears in Wednesday's issue of the journal PLOS ONE.

(Davison doesn't just study snails, he serves them as well. His preferred method is to cook them briefly in boiling water, take out the body, add garlic butter, slip them back in the shell, then oven-cook the lot for about 5 minutes. Though, he adds, "barbecuing would also work.")

Steve Jones, an evolutionary biologist at University College London, says the study demonstrates that "history and genes go together."

"This work suggests quite strongly that they were taken to Ireland by Spanish people, which is still a bit weird, because why would they do it?" Jones said, "[If this was] anywhere else you'd think they were mad," but in parts of France and Spain, where cave dwellings with millions of snail shells have been discovered, there's strong evidence that snails were a dietary staple. As Jones explained: "What's easier, to chase down a woolly mammoth and eat it, or pick up a lot of snails?"

When those cave dwellers moved, they may have taken snails along. "While they weren't the first humans, this lot came from France ... without stopping along the way," Davison explained. If they stopped en route to go ashore for long, the snails would have died, or been found in other parts of Europe, too. "It tells you about a single event," he said.

Davison and Adele Grindon (then a graduate student at the University of Nottingham) spent two years collecting samples of the snail species Cepaea nemoralis from Ireland, Britain, Northern Spain and Southern France. Then they analyzed the mitochondrial DNA of the specimens — an easy section to sequence, Davison explained. They found seven snail lineages around Europe, one of which was unique to only two places: Ireland and the slopes of the Pyrenees.

It's somewhat puzzling that snails are found on some far-flung islands, including Ireland. "If they find themselves in the sea, they die, and they can't fly," Davison said. "So how on earth do you these remote islands with snails on them?" It's possible that birds could have carried the Irish land snails over, but it's unlikely. "It would have to be a very big bird and a very sticky snail," Davison said.

Ireland was swept near clear of animal and plant life during the last ice age. "Most of what we had went extinct," Allan McDevitt, who studies the genetics and invasion histories of the greater white-toothed shrew at University College Dublin, told NBC News. When the ice sheets pulled north, flora and fauna that made it back to the island either toughed out the cold, hopped a ride on air or ocean currents, or were carried over by birds. As for larger, land-living animals, "It has been people who've played a most important role in bringing the animals here," McDevitt said.

But the origins of Ireland's present-day wildlife pose a riddle for biologists. The island is a melting pot of migrants, some of which seem to have hopped over from nearby Britain, while others hint at ancestors in southwestern Europe. "To understand how that has come about has been quite a puzzle," Jeremy Searle, an evolutionary biologist at Cornell University, told NBC News. Which is why studies like Davison's are important: "To actually pinpoint a specific area where [an] Irish species has come from is very exciting."

Adele Grindon and Angus Davison are the authors of "Irish Cepaea nemoralis Land Snails Have a Cryptic Franco-Iberian Origin That Is Most Easily Explained by the Movements of Mesolithic Humans" published in the June 19 issue of PLoS One.
