Genetic patterns of world’s farmed, domesticated foxes revealed through historically in-depth research

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

The animals we have domesticated have generally been domesticated for so long that there is no easy way to go back and study the transition from wild to domestic. One notable exception is the domestication of red foxes, which were raised in captivity for their fur. This began in 1896 on Prince Edward Island in Canada. A team from the University of Illinois Urbana-Champaign has followed the process from the island beginnings to captive fox populations around the world, including some that are still active today.

The work has been published in the Journal of Heredity.

“We have the historical records, we have genetic information on wild fox populations around the world, and we have samples from foxes that have bred 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 lead study author Halie Rando, an assistant professor at Smith College who completed her doctoral research at the Illinois Informatics Institute, now in the School of Information Sciences, in Illinois.

Rando, along with Anna Kukekova, a professor of animal science at the University of Illinois, 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 data relating to the intercontinental fox trade, changing fur demands and farm sizes, and breeding practices. Together, the data allowed them to determine the geographic origins of captive foxes worldwide and understand the role of genetic diversity in the domestication process.

“When we do population genetics studies, we can forensically uncover history,” Rando said. “By looking at signatures that exist in current populations, we can make inferences about the past.”

Early fox farmers were motivated by the demand for the silvery variety of red foxes. Capturing rare silver foxes in the wild was unreliable and difficult, but breeding them in captivity had its own challenges.

“The foxes were very difficult to breed on the farms because they would get very stressed and die or kill their offspring. It took them a long time to figure out how to set up the breeding enclosures to reduce stress. Along the way, they selected individuals that were better suited to the farm environment,” Rando said. “They also managed to select for the silver coat color. Even without any knowledge of genetics, they figured out how to crack the code.”

The industry then boomed, with Canadian foxes exported around the world. Genetic analysis showed that every captive population the researchers examined, even those in Eurasia, was derived from wild North American foxes. There were not even traces of genetic markers from Eurasian wild fox populations, suggesting that any attempts to domesticate local populations were abandoned or overtaken by North American genetics.

“This study helps answer questions that researchers have been asking for years about the geographic origins and genetic background of these fox populations,” Kukekova said. “In addition, some farm foxes may have mixed with native foxes through releases in different locations over the years. Sometimes unexpected gene signatures emerge in native populations, so our study may help explain where they come from.”

World War II interrupted demand and the industry never recovered in North America. In the USSR, however, fox farms quickly recovered, aided by the government-supported fur industry.

Overall, the genetic pattern reflects the more stable history of breeding in Eurasia. Although all of the captive-bred foxes in the study appeared to be descended from North American wild foxes, the populations in Eurasia were more genetically diverse, with a greater representation of Alaskan and western U.S. genotypes in addition to common genotypes from eastern Canada.

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

The study also sheds light on the famous Russian Farm Fox experiment, which began in 1959 at the Institute of Cytology and Genetics (ICG) in Novosibirsk. The study began by selecting farm-raised foxes that showed the least avoidance behavior around people. Over successive generations, scientists selectively bred foxes with tame behavior, eventually resulting in foxes that were as friendly as the family dog.

The current study sampled that population and analyzed it along with the others, finding no unique genetic origins for the Russian foxes. According to Rando, this suggests that farm-raised foxes may have the same underlying capacity to develop friendly behavior.

“I would say we have shown quite convincingly that the Novosibirsk foxes are not fundamentally different from other farm-bred foxes in terms of their genetic origins. We also found that the Novosibirsk populations were among the most genetically diverse populations in captivity, probably due to their accurate pedigree records and carefully planned breeding,” she said.

Kukekova added: “It’s informative to know that this one successful venture in Prince Edward Island really had a huge effect on modern populations that continues to this day. The model can help us study domestication broadly and find gene networks that lead to tame behavior, something that people have been interested in for a long time.”