September 12, 2012

Globe-Trotting Foxes Crossed Arctic Land Bridge

John Neumann for — Your Universe Online

Sometime between 200 and 500 years ago, in the throes of a mini ice age, sea ice had become thick and stable enough for animal migration to occur between regions in far northern Europe. This sheet of ice gave arctic foxes a migration route to Iceland from previously unavailable landmasses, including present-day Russia, North America and Greenland.

Scientists at Durham University reported findings highlighting the importance of sea ice in creating and maintaining the genetic population of the arctic fox across the polar regions where the animal is found. This project could aid in tracking the migration of other animals found on remote islands, the researchers said.

Iceland maintains approximately 10,000 arctic foxes and they are not considered to be in danger. The researchers noted, however, that the animals increasing isolation from the rest of the Arctic, caused by warmer temperatures and a lack of sea ice, could further differentiate the island´s population from their mainland relatives.

There is evidence in the ancient past of arctic foxes also crossing sea ice during previous cold spells, reaching the island well before human settlement in the 9th Century. When warmer temperatures melted the sea ice, the ancient foxes became stranded on the island before the Little Ice Age reconnected Iceland to the mainland.

DNA samples from ancient remains of Icelandic arctic foxes were analyzed, dating from the late 9th to 12th Century archaeological sites, and the researchers compared the findings to DNA data from modern fox examples.

The DNA of the ancient foxes was found to share a single genetic signature, while the modern population possesses five unique signatures.

Senior author Dr. Greger Larson, in Durham University´s Department of Archaeology, said, “During the Little Ice Age there was a great deal more sea ice in the North Atlantic than there is today and during the late 18th and 19th centuries sea ice routinely grounded on Iceland.”

“Even today arctic foxes routinely travel hundreds of miles across sea ice and once the ice bridge was in place, they easily crossed the North Atlantic and were able to arrive on Iceland, increasing the genetic diversity of the population.”

Larson and his fellow researchers ruled out differences in the amount of variation of the ancient foxes for geographic reasons and breeding between farmed and wild arctic foxes. The team concluded that the most likely explanation for the boom in genetic diversity among arctic foxes was migration across sea ice that formed during the Little Ice Age.

Larson continued saying, “Without the sea ice, there will be no new fox migrants and thus the Icelandic population will continue to diverge from their mainland relatives.”

The model the researchers used to determine the genetic diversity of the arctic fox could also be used to track the historical migration of other animals such as reindeer that are also found on Iceland.

The research, partly funded by the Natural Environment Research Council (NERC), is published in Proceedings of the Royal Society B - Biological Sciences.