Red deer (<i>Cervus elaphus</i>, shown) that once lived on remote Scottish islands may have been introduced from distant sites by Stone Age seafarers thousands of years ago.

Red deer (Cervus elaphus, shown) that once lived on remote Scottish islands may have been introduced from distant sites by Stone Age seafarers thousands of years ago.

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Red deer came to Scottish islands from unexpected places

Stone Age seafarers may have transported red deer to far-flung Scottish islands from remote sites in Europe rather than from the Scottish mainland nearby, a new study suggests. Although researchers have long suspected the creatures had been brought to the remote isles by humans to provide a steady supply of food, antlers, or skins, the notion they originated in distant lands and were carried there in a sort of Neolithic ark is a surprising twist.

Red deer (Cervus elaphus) are one of the most widespread large mammals in Europe today, missing only from Iceland and northern Scandinavia. Each deer can grow up to twice the weight of North America’s white-tailed deer, and the animals now number between 360,000 and 400,000 in Scotland alone, says David Stanton, an evolutionary biologist at Cardiff University in the United Kingdom. Remains unearthed at many archaeological sites throughout Scottish mainland and its islands suggest the deer have been an important source of meat, pelts, and bones for thousands of years. Their bones have even turned up in middens, or archaeological trash piles, dating back to at least 4500 years ago on Orkney, an island that lies about 16 kilometers off the northeastern coast of Scotland, and on the Outer Hebrides, a small archipelago located about 25 kilometers off the northwestern coast.

At first glance that’s a surprise, because red deer probably can’t swim more than 7 kilometers across open water, Stanton says. Even when sea levels were at their lowest, about 22,000 years ago at the height of the last ice age, the islands were likely out of the deer’s swimming range. Before that time, Orkney and the Hebrides were covered with ice. So, researchers suggest, any red deer on those islands—and many other landlubber creatures now there, too, like the Orkney vole, a tiny rodent found only on the islands of its namesake archipelago—must have been brought there by humans.

To find out where the deer might have come from, Stanton and his colleagues analyzed genetic material from 74 red deer bones—some up to 7500 years old—that had been found at archaeological sites on the Scottish mainland, Orkney, and the Inner and Outer Hebrides. Then they compared the results with previous analyses of ancient DNA from red deer in Norway, Ireland, and Italy, as well as those from modern specimens throughout Europe. Today’s red deer, which recolonized Europe after the ice sheet melted about 12,000 years ago, fall into three or four distinct lineages that likely correspond to separate southern regions to which the deer had retreated during the height of the ice age, Stanton says.

The team looked at a certain section of mitochondrial DNA extracted from 0.5-gram bone samples about half the size of a sugar cube. (Mitochondria, the tiny energy factories found in every cell, have genetic material separate from that found in the cell’s nucleus.) Because the segment of DNA that they studied isn’t associated with a gene that conveys an obvious benefit to the deer, any mutations that arise over time neither help nor hurt the creature’s survival. They do, however, provide researchers with insights about how various populations may be related to each other.

In the 46 bone samples that yielded results in the new study, the team’s tests uncovered 14 different haplotypes, or particular sets of genetic variation, 10 of which had never been seen in previous studies. All 10 of the novel haplotypes were found on the outer Scottish islands. Possibly more telling, the deer found on the Outer Hebrides don’t sport the haplotypes found on the Scottish mainland or on the isles of the Inner Hebrides (which are within swimming distance of the mainland, Stanton notes). That disparity strongly suggests that the ancient Outer Hebridean deer, as well as their genetically distinct kin on the island of Orkney, originated in distant locales that haven’t yet been identified, the team reports online today in the Proceedings of the Royal Society B.

Although possible sources of the deer are far from clear, they likely originated somewhere in western continental Europe, Stanton says. That’s because their overall genetic profile matches deer now living in that region.

Why would people go to the bother of transporting the deer from a remote locale rather than nearby Scotland? Moving deer from what seems to be an obvious choice may not have been feasible, Stanton explains. Maybe the deer elsewhere were easier to catch, he notes, or maybe there were social or cultural reasons that Scottish deer were off limits. Or, he adds, if the seafarers themselves were from a distant land, they might have simply brought them along.

The team’s analysis “is a great piece of work,” says Ceiridwen Edwards, an archeogeneticist at the University of Huddersfield in the United Kingdom. Whereas previous consensus among researchers has been that red deer and several domestic species spread to the islands from England, she notes, “it is exciting to think that introductions from places further north in Europe could also have had an input into the red deer island gene pool.” The previously unknown genetic diversity could stem from repeated introductions of the deer to the islands over time from several locations by waves of seafaring hunters or settlers. Or, she notes, populations may have grown from a large group of genetically diverse deer brought to the remote islands at one time.

However, Edwards cautions, there may be an alternate explanation for the genetic diversity seen in the new study. It’s possible, she suggests, that previous studies of ancient DNA didn’t analyze enough samples to unearth the true amount of genetic diversity in the region’s red deer.

But that’s not likely, Stanton counters. Indeed, he notes, it’s improbable that all of the previous genetic studies of red deer, including those living throughout Europe today, wouldn’t have picked up any of the haplotypes he and his team identified in their new research.

When it comes to identifying the migrations and movements of ancient seafarers and the creatures they may have carried with them, “our results really just scratch the surface,” he says. “Our study raises as many questions as it does answers.”

Future studies should include samples from more sites in England as well as continental Europe, the researchers propose. Those results could provide better understanding of how those deer are related to those in the Inner Hebrides, as well as deliver more information about how deer populations on the islands have fluctuated in the past few millennia.