Foxes bred to be friendly have fewer neurons in a brain region linked to aggression

Foxes bred over decades to be friendly toward people have fewer of a type of brain cell linked to aggression, according to a study in Current Biology, the Cornell Chronicle reported on 2 November. The difference shows up in the ventromedial hypothalamus, a region at the base of the brain.

A breeding experiment that began in the 1950s

In the late 1950s, Russian geneticists in Siberia noticed that some silver foxes on fur farms were friendlier toward their keepers than others. They bred the friendliest foxes together, and after six generations some litters included pups that sought out contact with people. The tamer foxes also developed traits seen in domesticated animals, such as floppy ears and shorter snouts. The breeding has continued for decades.

Fewer neurons in the aggression circuit

The Cornell team compared nine fox brains: three from tame foxes, three from foxes bred for aggression and three from wild foxes. They sliced the preserved brains very thinly and used a fluorescent technique called RNAscope to identify different cell types. Tame foxes had fewer neurons carrying estrogen receptor alpha in the ventromedial hypothalamus, a cell type earlier shown to be part of the aggression circuit in mice.

“If you activate them, the mouse will immediately attack another mouse.” — Eirene Markenscoff-Papadimitriou, Cornell University, on the neurons in mice

The research was led by Eirene Markenscoff-Papadimitriou, assistant professor of molecular biology and genetics, with first author Jared Klein, a former technician in her lab, and colleagues from Cornell, the University of Illinois Urbana-Champaign and the Institute of Cytology and Genetics of the Russian Academy of Sciences.

Rapid change, still unexplained

The authors say the work shows how strong selection can change brain structure on short timescales. Why domestication changes this region is the next question; co-author Anna Kukekova may study how changes in the genome affect these neurons. The study was small, nine brains in total. More stories about animal minds are collected under animal behavior.