Domestication effect of reduced brain size is reverted when mink become feral

A typical consequence of breeding animal species for domestication is a reduction in relative brain size. When domesticated animals escape from captivity and establish feral populations, the larger brain of the wild phenotype is usually not regained. In the American mink (Neovison vison), we found an exception to this rule. We confirmed the previously described reduction in relative braincase size and volume compared to their wild North American ancestors in mink bred for their fur in Poland, in a dataset of 292 skulls. We then also found a significant regrowth of these measures in well-established feral populations in Poland. Closely related, small mustelids are known for seasonal reversible changes in skull and brain size. It seems that these small mustelids are able to regain the brain size, which is adaptive for living in the wild, and flexibly respond to selection accordingly.

Automated summary

A common outcome of breeding animals for domestication is a decrease in relative brain size. However, the American mink bred for fur in Poland showed an exception to this pattern. While their domesticated counterparts had reduced brain size compared to their wild ancestors, well-established feral populations of mink in Poland exhibited a significant regrowth in brain size. This suggests that closely related small mustelids are capable of adapting and responding to selection by regaining their brain size for survival in the wild.