2023-07-10 08:47:52
A study by the Max Planck Institute for Animal Behavior (MPI-AB) has discovered a rare reversal of the domestication effect.
Over the course of captive breeding, the American mink experienced a reduction in relative brain size, but populations that escaped captivity were able to regain almost full ancestral brain size within 50 generations. The study is published in the Royal Society Open Science.
“Our results show that the loss of brain size is not permanent in domestic animals,” says Ann-Kathrin Pohle, a master’s student at MPI-AB and first author of the paper. “This finding deepens our understanding of how domestication has changed the brains of animals and how these changes might affect animals when they return to the wild.”
When animals lose brain size during the course of domestication, it is mostly considered to be a one-way street. Animals almost never seem to regain the relative brain size of their ancestral forms, even in wild populations that have been living in the wild for generations. “Once animals lose parts of their body, such as certain brain regions, over the course of evolution, they are gone and cannot simply be recovered,” says Dina Dechmann, lead author of the paper and group leader at MPI-AB. .
Studying whether or not wild animals can recover the relative brain size of their wild counterparts is also methodologically difficult. To do it correctly, Dechmann says, “you would need to find an animal with separate wild and feral populations to reduce the chance that the groups may have mixed. And you would need to find an animal that might be studied through enough brain and skull measurements. You would need an animal, in other words, like the American mink”.
Native to North America, the American mink has been domesticated for the fur trade for more than a century. After they were bred in Europe for fur farming, the captive animals escaped to form feral populations that have spread throughout Europe. This natural history provided the separate populations Dechmann and his team needed: wild mink from North America, domesticated mink from European fur farms, and wild mink from Europe.
To explore changes in brain size, the team turned to a proxy: skulls. “Brain size is a good indicator of brain size in mink, and this allows us to take measurements from existing skull collections without the need for live animals,” says Pohle. A museum collection from Cornell University was used to study skulls of wild American mink, while European fur farms provided skulls of domesticated animals.
For the wild population, Dechmann and Pohl collaborated with Andrzej Zalewski at the Polish Center for Mammal Research, who had a collection of skulls obtained from a wild mink eradication program. “Usually the difficulty with skull studies is finding large enough collections to work with,” says Dechmann. “We were incredibly fortunate to work with several organizations to get the population samples we needed.”
The team took measurements of the skulls to calculate the relative size of the animals’ brains. They found that, consistent with the well-documented domestication process, the brains of captive-bred mink had shrunk by 25% compared to their wild ancestors. But, in contrast to expectations, the brains of wild mink grew back to almost wild size within 50 generations.
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