222 — A longitudinal study of phenotypic changes in early domestication of house mice

Domestication syndrome is a bizarre change to a population that occurs when the individuals are exposed to humans for prolonged periods of time. This syndrome includes phenotypic changes like changes to pigmentation (brown house-mice develop white patches of fur) and even morphological changes (the snouts and brains of house-mice and even domesticated dogs shrink in length).

In 2002, a study population of a dozen wild mice were caught and allowed to live in an uninhabited barn in Switzerland. Over the course of a decade and more than 20 generations, the mouse populations grew to around 300 individuals, with around ~5 mice per square meter. The mice were handled a few times throughout their life according to standard laboratory-mouse handling procedures.

Over the course of the study, the mouse head lengths decreased significantly, and the occurrence of white patches of fur more than doubled between 2010 and 2016. Periodic analyses suggested that inbreeding and genetic drift were not enough to account for these phenotypic changes.

When we use lab mice or other model animals to validate our biomedical claims, we rely on the assumption that these animals are close analogs to our expected “wild-type” lineages. These observations are interesting because they suggest that domestic mice are in some way different from their wild cousins, and this difference manifests in some seemingly unimportant (e.g. fur color) and some very important (e.g. brain size) ways.