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American mink reverses domestication effect, regains brain size

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Farm animals exhibit a consistent difference from their wild ancestors: their brains are relatively smaller. This phenomenon, known as the domestication effect, is evident in various domesticated species such as sheep, pigs, and cows.

In a groundbreaking study conducted by the Max Planck Institute of Animal Behavior (MPI-AB), researchers have discovered a remarkable reversal of the domestication effect. Through captive breeding, the American mink experienced a reduction in relative brain size. However, when certain populations escaped from captivity and returned to the wild, they were able to regain nearly their full ancestral brain size within just 50 generations. This extraordinary finding has been published in the prestigious journal Royal Society Open Science.

Ann-Kathrin Pohle, a Master’s student at MPI-AB and the paper’s first author, emphasizes the significance of these results: “Our study demonstrates that the loss of brain size in domesticated animals is not a permanent change. This discovery deepens our understanding of how domestication has influenced the brains of animals and how these changes might impact them upon reintroduction to the wild.”

Understanding the feral brain

When animals undergo domestication, the reduction in brain size is typically considered irreversible. Even in feral populations that have been living in the wild for generations, animals rarely regain the relative brain sizes of their ancestral forms. Dina Dechmann, a group leader at MPI-AB and the senior author of the paper, explains, “Once animals lose certain parts of their body, such as specific brain regions, throughout evolution, they are lost and cannot be regained.”

Methodologically, studying whether feral animals can regain the relative brain sizes of their wild counterparts is challenging. Dechmann states that to conduct such research, “you would need to find an animal with distinct wild and feral populations to minimize the chance of intermixing between the groups. Additionally, you would need an animal that allows for sufficient brain and skull measurements.” The American mink, in this case, fulfills these requirements.

The American mink, native to North America, has been domesticated for fur farming for over a century. After being bred in Europe for this purpose, captive minks escaped and formed feral populations that have since spread throughout Europe. This natural history provided the perfect opportunity for Dechmann and her team to study separate populations: wild mink from North America, domesticated mink from European fur farms, and feral mink from Europe.

To examine changes in brain size, the researchers used a proxy measurement: skulls. Ann-Kathrin Pohle notes, “Braincase size serves as a reliable proxy for brain size in minks, allowing us to measure existing skulls from museum collections without the need for live animals.” The team utilized a collection of wild American mink skulls from Cornell University and obtained domesticated mink skulls from European fur farms.

For the feral population, Dechmann and Pohle collaborated with Andrzej Zalewski at the Polish Mammal Research Centre, who possessed a collection of skulls obtained during an eradication program targeting feral mink. Dechmann remarks, “Typically, the challenge with skull studies lies in finding sufficiently large collections to work with. We were extremely fortunate to collaborate with multiple organizations to obtain the necessary population samples.”

By measuring the skulls, the team calculated the relative brain size of the mink. They discovered that, in line with the well-documented process of domestication, the brains of captive-bred mink had reduced by 25% compared to their wild ancestors. However, contrary to expectations, the brains of feral mink had almost fully regained their wild size within just 50 generations.

Flexible brains

Dechmann has a compelling hypothesis as to why the American mink has achieved this unexpected reversal. These minks belong to a family of small mammals that possess a remarkable ability to undergo seasonal changes in brain size, known as Dehnel’s phenomenon. Dechmann, an expert in this phenomenon, has previously observed it in shrews, moles, and weasels.

While other domesticated animals appear to experience a permanent loss in brain size, the mink may be capable of regaining their ancestral brain sizes due to their inherent flexibility in brain size regulation. Dechmann explains, “It’s possible that mink can restore their brain sizes because they possess the ability to modulate their brain size as part of their natural biology.”

This flexibility in brain size could have provided advantages to mink reintroduced to the wild. Dechmann suggests, “When escaping from captivity and returning to their natural habitat, animals would benefit from having a fully functional brain to navigate the challenges of wild living. Animals like minks, with adaptable brain sizes, may be able to restore their brains even if they had previously experienced shrinkage.”

Although the study’s findings do not shed light on whether the brains of feral mink function similarly to those of their wild counterparts, further investigation would be required to explore this aspect in future studies. Examining the actual brains of the animals would be necessary to determine if the feral mink exhibit the same brain functionality as their wild counterparts.

Source: Max Planck Society

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