Domestication is the process of adapting animals to human needs and preferences, such as for food, companionship, or work. It often involves changes in the animals' appearance, behavior, and physiology, including their brain size.
Many domesticated animals have smaller relative brain sizes than their wild ancestors, a phenomenon known as the domestication effect.
However, a recent study by the Max Planck Institute of Animal Behavior (MPI-AB) and their collaborators has discovered a rare exception to this rule: the American mink.
The study, published in the Royal Society Open Science, shows that feral mink that escaped from fur farms in Europe were able to regrow their brains almost to the size of their wild relatives in North America.
How domestication affects brain size
(Photo : JENS SCHLUETER/DDP/AFP via Getty Images)
The domestication effect on brain size is thought to be a result of relaxed natural selection and artificial selection by humans, as per Phys.org.
In the wild, animals face various challenges and pressures that require cognitive abilities, such as finding food, avoiding predators, and navigating complex environments.
These abilities depend on the size and function of certain brain regions, such as the cerebrum and the cerebellum. Therefore, natural selection favors larger brains in wild animals.
In contrast, domesticated animals live in more predictable and controlled environments, where they depend on humans for food, shelter, and protection.
They also face less competition and aggression from conspecifics, as humans select for docile and cooperative traits.
These factors reduce the need for cognitive abilities and brain regions that are associated with them. Therefore, domesticated animals experience a reduction in brain size over generations of breeding.
The domestication effect on brain size has been observed in many species of farm animals, such as sheep, pigs, cows, horses, and dogs. It has also been observed in some captive-bred animals, such as foxes and mink.
However, it is not clear whether this effect is reversible or permanent. If domesticated animals escape or are released into the wild, can they regain their ancestral brain size?
How feral mink regrow their brains
The American mink is a small carnivorous mammal that belongs to the weasel family. It is native to North America, where it lives in wetlands and forests near water sources, as per Eurekalert.
It feeds on fish, birds, rodents, and other small prey. It has a thick fur coat that varies in color from brown to black.
The American mink has been domesticated for over a century for its fur. It was introduced to Europe for fur farming in the early 20th century.
However, some mink escaped from captivity or were released by animal rights activists into the wild.
These feral minks have established populations throughout Europe, where they compete with native species and cause ecological damage.
The MPI-AB researchers and their collaborators took advantage of this natural history to study the effects of domestication and feralization on brain size in mink.
They compared three groups of mink: wild mink from North America (the ancestral form), domesticated mink from European fur farms (the derived form), and feral mink from Europe (the reverted form). They measured the braincase size of each group as a proxy for brain size.
They found that domesticated mink had significantly smaller relative brain sizes than wild mink, confirming the domestication effect.
However, they also found that feral mink had significantly larger relative brain sizes than domesticated mink, almost reaching the level of wild mink.
This suggests that feral mink were able to regrow their brains within 50 generations of living in the wild.
Also Read: European Mink Found Refuge After Being Pushed to the Brink of Extinction
Why feral mink regrow their brains
The researchers proposed several possible explanations for why feral mink regrow their brains.
One possibility is that natural selection favors larger brains in feral mink because they face more challenges and pressures than domesticated mink.
For example, feral mink have to find food, avoid predators, and adapt to new habitats and climates.
Another possibility is that genetic drift or gene flow contributes to the increase in brain size in feral mink.
Genetic drift is a random change in allele frequencies due to chance events such as mutations or bottlenecks. It is the exchange of alleles between populations due to migration or interbreeding. Both processes can introduce genetic variation that affects brain size.
A third possibility is that epigenetic mechanisms play a role in regulating brain size in feral mink.
Epigenetics refers to changes in gene expression that do not involve changes in DNA sequence but are influenced by environmental factors such as stress or nutrition. It can be inherited across generations and can affect brain development and function.
The researchers suggested that a combination of these factors may be involved in the reversal of the domestication effect on brain size in feral mink.
They also noted that American mink belong to a family of small mammals with a remarkable ability to seasonally change their brain size in a process known as Dehnel's phenomenon.
Dina Dechmann, the senior author of the paper and an expert on this process, has documented Dehnel's in shrews, moles, and weasels. She speculated that this phenomenon may facilitate the rapid adaptation of brain size in feral mink.
Related article: Mink Workers Infected With Coronavirus First Known Cases of Animal-Human Transmission
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