Genetic patterns of worldwide bred, domesticated foxes revealed through historical deep diving

Domesticated animals play an important role in our society, with two-thirds of American families enjoying the company of pets and many others relying on animal products for their nutritional needs. But the process of domestication remains a bit of a mystery. Convincing wild animals that they are safe enough to coexist and mate in enclosures and in close proximity to humans and other animals is no small feat. What does it take behaviorally and genetically for this to happen?

The animals we have domesticated have been largely docile for so long that there is no easy way to go back and study the transition from wild to tame. A notable exception is the domestication of red foxes—bred in captivity for their fur—since 1896 in Prince Edward Island, Canada. The University of Illinois Urbana-Champaign team traced the process from its origins on the island to captive fox populations around the world, including some that are still in operation today.

The work is published in Journal of Heredity.

“We have historical documents, we have genetic information on wild fox populations around the world, and we’ve obtained samples from domesticated foxes in North America and Eurasia. So we can really dig into the question of how foxes were domesticated and how their genetics were shaped by geography and time, ” said the study’s lead author Halie Rando, an assistant professor at Smith College who completed her doctoral research at the Illinois Information Institute, now in the School of Information Sciences at Illinois.

Rando, along with Illinois professor of animal sciences Anna Kukek and their collaborators, analyzed new and previously published mitochondrial DNA data from wild fox populations and from 10 captive populations in North America and Eurasia, including the site of the famous Russian fox domestication experiment. They then cross-referenced historical records related to the intercontinental fox trade, changing demand for furs, and farm sizes and husbandry practices. Together, the data allowed them to determine the geographic origins of domesticated foxes around the world and understand the role of genetic diversity in the domestication process.

“When we do population genetics research, we’re able to uncover history forensically,” Rando said. “By looking at the signatures that are in the current population, we can make inferences about the past.”

The first fox breeders were motivated by the demand for a silver variant of red foxes. Attempting to capture rare silver foxes from the wild was unreliable and difficult, but breeding them in captivity had its own problems.

“Foxes were very difficult to farm because they were really stressed and they died or killed their offspring. It took them a long time to figure out how to set up breeding enclosures to reduce stress. They selected individuals that were better suited to the farm environment, ” Rando said. “They also managed to pick out a silver coat. Even without knowing genetics, they figured out how to crack the code.”

Then the industry boomed and Canadian foxes were exported all over the world. Genetic analysis showed that every captive population the researchers examined—even those in Eurasia—descended from wild North American foxes. In fact, there were no traces of genetic markers from Eurasian wild fox populations, suggesting that any attempts to domesticate local populations were abandoned or overcome by North American genetics.

“This study helps answer questions researchers have had for years about the geographic origin and genetic background of these fox populations,” said Kukeková. “Additionally, some farmed foxes may have interbred with native foxes in different places over the years. Sometimes unexpected gene signatures appear in native populations, so our study can help explain where they came from.”

World War II interrupted demand and the industry never recovered in North America. However, in the USSR, fox farms quickly recovered, with the help of a government-sponsored fur industry.

Overall, the genetic pattern reflects a more stable breeding history in Eurasia. Although all domesticated foxes in the study were found to be descended from North American wild foxes, populations in Eurasia were more genetically diverse, with greater representation of genotypes from Alaska and the western US in addition to common genotypes from eastern Canada.

“Some gene signatures were very rare and only found in certain Eurasian farm populations,” Rando said. “The presence of these rare signatures, along with greater diversity overall in Europe, could be due to more stable population sizes there after World War II, while these rare types may have been lost when North American farms collapsed.”

The study also sheds light on the famous Russian Farm Fox experiment, started in 1959 at the Institute of Cytology and Genetics (ICG) in Novosibirsk. The study was based on a selection of farm-raised foxes that showed the least avoidant behavior around humans. Over the following generations, scientists selectively bred foxes with tame behavior, eventually resulting in foxes as friendly as the family dog.

The current study sampled this population and analyzed it along with others, finding no unique genetic ancestry for Russian foxes. To Rand, this suggests that farmed foxes may have the same basic ability to develop friendly behavior.

“I would say that we have shown quite convincingly that the Novosibirsk foxes are not significantly different from other farmed foxes in terms of their genetic background. We also found that the Novosibirsk populations were among the most genetically diverse in captivity, probably due to their careful record of origin and carefully planned breeding,” she said.

Kukek added: “It’s informative to know that this one successful effort in Prince Edward Island really had a huge impact on modern populations that continues to this day. This model can help us study domestication more broadly and find the gene networks leading to domesticated behavior, which is something which people have been wondering about for a very long time.”