The domesticated silver fox (marketed as the Siberian fox) is a domesticated form of the silver morph of the red fox. As a result of selective breeding, the new foxes became not only tamer, but more dog-like as well.
The result of over 50 years of experiments in the Soviet Union and Russia, the breeding project was set up in 1959[1] by Soviet scientist Dmitri Belyaev. It continues today at The Institute of Cytology and Genetics at Novosibirsk, under the supervision of Lyudmila Trut.
The Russian researchers have partnered with the American company SibFox to distribute these foxes as pets internationally.[2]
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The experiment was initiated by scientists who were interested in the topic of domestication and the process by which wolves became tame domesticated dogs. They saw some retention of juvenile traits by adult dogs, both morphological ones, such as skulls that were unusually broad for their length, and behavioral ones, such as whining, barking, and submission.
In a time when Lysenkoism was an official state doctrine, Belyaev's commitment to classical genetics had cost him his job as head of the Department of Fur Animal Breeding at the Central Research Laboratory of Fur Breeding in Moscow in 1948.[3] During the 1950s, he continued to conduct genetic research under the guise of studying animal physiology.
Belyaev believed that the key factor selected for in the domestication of dogs was not size or reproduction, but behavior; specifically, amenability to domestication, or tameability. He selected for low flight distance, that is, the distance one can approach the animal before it runs away. Selecting this behavior mimics the natural selection that must have occurred in the ancestral past of dogs. More than any other quality, Belyaev believed, tameability must have determined how well an animal would adapt to life among humans. Because behavior is rooted in biology, selecting for tameness and against aggression means selecting for physiological changes in the systems that govern the body's hormones and neurochemicals. Belyaev decided to test his theory by domesticating foxes; in particular, the silver fox, a dark color form of the red fox. He placed a population of them in the same process of domestication, and he decided to submit this population to strong selection pressure for inherent tameness.[4]
The result is that Russian scientists now have a number of domesticated foxes that are fundamentally different in temperament and behavior from their wild forebears. Some important changes in physiology and morphology are now visible, such as mottled or spotted colored fur. Many scientists believe that these changes related to selection for tameness are caused by lower adrenaline production in the new breed, causing physiological changes in very few generations and thus yielding genetic combinations not present in the original species. This indicates that selection for tameness (i.e. low flight distance) produces changes that are also influential on the emergence of other "dog-like" traits, such as raised tail and coming into heat every six months rather than annually.
The project also investigated breeding vicious foxes to study aggressive behavior. These foxes snap at humans and otherwise show no fear.
Following the demise of the Soviet Union, the project has run into serious financial problems. In 1996, there were 700 domesticated foxes, but in 1998, without enough funds for food and salaries, the number had to be reduced to 100. Most of the project expenses are covered by selling the foxes as pets, but the project remains in a difficult situation and is looking for new sources of revenue from outside sources.
In an article published in Current Biology about the genetic differences between the two fox populations,[5] an experiment was reported in which DNA microarrays were used to detect differential gene expression between domesticated foxes, non-domesticated foxes raised at the same farm as the tame foxes, and wild foxes. Forty genes were found to differ between the domesticated and non-domesticated farm-raised foxes, although about 2,700 genes differed between the wild foxes and either set of farm-raised foxes. The authors did not analyze the functional implications of the gene expression differences they observed.
In another study published in Behavior Genetics,[6] a system of measuring fox behavior was described that is expected to be useful in QTL mapping to explore the genetic basis of tame and aggressive behavior in foxes.