Outfoxing the Red Fox

About 300,000 years ago, during the last big Ice Age, a small red creature traversed the deep snow of what is now the Rocky Mountains. Furry paws, a thick coat and a knack for survival helped the red fox thrive in the glacial environment.

The adaptable descendants of these first native foxes still live in the mountains of western North America. In fact, red foxes are among the most widely distributed land carnivores in the world, spanning most of the Northern Hemisphere, as well as parts of Australia and northern Africa.

But a group of red foxes in Nevada’s Great Basin National Park is particularly special. Preston Alden, a graduate student at the University of California, Davis, is discovering just how important these red foxes are: They belong to a distinct lineage native to western North America, but they may be disappearing faster than you can say “quick brown fox.” Before Alden conducted this Western National Parks Association-funded study, not much was known about these foxes.

Red foxes are divided into distinctive subspecies. Today, most of the foxes that live at low elevations in western North America are invasive subspecies that were released or escaped from fur farms and spread across the country like wildfire. Some of the few remaining native subspecies in North America live in the Sierra Nevada, Rocky Mountains, and Great Basin mountain ranges.

Because of their abundance, Alden said, “The non-native red foxes aren’t really that special, but those found at high elevation have a lot of adaptations that make them unique.” They sport a dark red or even silver/black coat, which helps them blend into their surroundings. Snowshoe-like paws prevent them from sinking into deep snow, and extra fur keeps them warm in cold, snowy habitats. These adaptations make Great Basin National Park, with its high peaks and long winters, prime territory for cold-loving native red foxes.

Alden had a strong hunch that the park’s red foxes weren’t your average fur farm escapees, so he set out to figure out where the foxes came from.

He wasn’t disappointed.

Alden spent three summers scouring the high reaches of the park for DNA samples of hair and scat. He collected 11 usable samples. “Sometimes that would be on old dirt roads, sometimes trails, and then when I would get up into habitat that I knew was good montane red fox habitat from previous work that I did with the Sierra Nevada red fox, I would spread out and search places like alpine meadows and around lakes above 9,000 feet,” he said.

Alden then analyzed two types of DNA in each sample. The mitochondria, which are the powerhouse of the cell, contain their own tiny piece of DNA. Mitochondrial DNA gives a good snapshot of a fox’s family tree because it is inherited only from the mother’s side and mutates at a much slower rate than the DNA in the nucleus of the cell, or nuclear DNA. Because the mitochondrial DNA conserves its form from generation to generation, scientists can identify the ancestry of a fox for many generations.

Nuclear DNA, on the other hand, provides a much more recent picture, such as what other group of foxes is most closely related to those in Great Basin National Park. Both types of DNA were used to figure out whether natives or hybrids are living in the park.

After comparing the samples collected in the park to those from across western North America, Alden concluded that the Great Basin residents were closely related to those first native foxes hundreds of thousands of years ago, not relatives of the invasive fur-farmed foxes. A follow-up study discovered at least 11 native red foxes living in Great Basin National Park.

That number might not seem like a lot, but any evidence of native red foxes is important. Like many organisms facing habitat loss because of climate change and human expansion, their numbers are plummeting. Add the threat of non-native red foxes, and you end up with one big mess. Alden’s research is vital for the management and conservation of a charismatic but rare animal.

By Nina Kolodij