Genetic patterns of farmed and domestic foxes around the world revealed through in-depth historical analysis

Pets play an important role in our society: Two-thirds of American families enjoy the companionship of pets, and many more rely on animal products for their nutritional needs. But the process of domestication remains 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 behaviorally and genetically does it take to make this happen?

Most of the animals we have domesticated have been docile for so long that it is difficult to go back and study the transition from wild to domestic. One notable exception is the domestication of red foxes, bred in captivity for their fur, which began in 1896 on Prince Edward Island in Canada. A team from the University of Illinois at Urbana-Champaign traced the process from its beginnings on the island to captive fox populations around the world, some of which are still active today.

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

Rando, Anna Kukekova, professor of animal sciences at Illinois, and their collaborators analyzed new and previously published mitochondrial DNA data from wild fox populations and 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, changes in fur demand and farm size, and husbandry practices. Together, the data allowed them to determine the geographic origins of farmed 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 in a forensic way,” Rando said. “By looking at the signatures present in current populations, we can make inferences about the past.”

Early fox breeders were motivated by demand for the silver variant of the red fox. Rare silver foxes were unreliable and difficult to capture from the wild, but breeding them in captivity presented its own challenges.

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

The industry then boomed, with Canadian foxes being exported around the world. Genetic analysis showed that all the captive populations the researchers studied, even those in Eurasia, were derived from wild foxes from North America. In fact, there was no evidence of genetic markers from wild fox populations in Eurasia, suggesting that all attempts to domesticate local populations were abandoned or overtaken by North American genetics.

“This study helps answer questions that researchers have had for years about the geographic origin and genetic makeup of these fox populations,” Kukekova said. “Additionally, some farm foxes may have mixed with native foxes during release events over the years in different locations. Sometimes, unexpected genetic signatures appear in native populations, so our study may help explain their origin.”

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

Overall, the genetic profile reflects the more stable breeding history in Eurasia. Although all farmed foxes studied were descended from wild foxes in North America, the Eurasian populations were genetically more diverse, with greater representation of Alaskan and western US genotypes in addition to common eastern Canadian genotypes.

“Some genetic signatures were very rare and were only present in some Eurasian farming populations,” Rando said. “The presence of these rare signatures, as well as the greater diversity in Europe, could be due to more stable population sizes after World War II, while these rare types may have disappeared 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 foxes raised on farms that exhibited the least avoidance behaviors toward humans. Over successive generations, the scientists selected foxes with docile behavior, eventually resulting in foxes as friendly as the family dog.

The current study sampled this population and analyzed it along with the others, without finding a unique genetic origin for Russian foxes. To Rando, this suggests that foxes raised on farms may have the same underlying ability to develop friendly behaviors.

“I would say we have demonstrated quite conclusively that the Novosibirsk foxes are not significantly different from other farm-raised foxes in terms of their genetic background. We also found that the Novosibirsk populations are among the most genetically diverse captive populations, likely due to their meticulous pedigree records and carefully planned breeding,” she said.

Kukekova added: “It is instructive to know that this successful initiative in Prince Edward Island had a significant impact on modern populations that continues today. The model can help us study domestication in general and find genetic networks that lead to docile behaviour, a topic that has interested humans for a very long time.”