Scientists discovered differences in aggression-linked brain cells in tame and aggressive foxes, offering new clues to how domestication changes the brain.<\/p>\n
For decades, scientists in Siberia have bred foxes that feel comfortable around people. <\/p>\n
By choosing the friendliest animals to have pups, generation after generation, they produced foxes with very different temperaments from their aggressive relatives.<\/p>\n
Now, a small study offers a clue to what changed in their brains. The friendly foxes had fewer of one kind of nerve cell in a specific brain region than foxes bred to be aggressive.<\/p>\n
These cells interest scientists because switching on the same kind of cell in mice makes them attack other mice. The fox study involved just nine brains, so it offers a starting point for understanding the change.<\/p>\n
Molecular biologist<\/a> Eirene Markenscoff-Papadimitriou, an assistant professor in Cornell University<\/a>\u2018s Department of Molecular Biology and Genetics, led the work with colleagues in the US and Russia. <\/p>\n \u201cWe wanted to understand, what are the neurological underpinnings of these changes in behaviors that occurred very rapidly with this selection,\u201d Markenscoff-Papadimitriou said.<\/p>\n How friendliness took hold<\/p>\n The experiment<\/a> began on silver fox farms in Siberia in the late 1950s. Silver foxes belong to the same species as red foxes but have a different coat color.<\/p>\n Geneticist Dmitry Belyaev and his colleagues noticed that some farmed foxes seemed more comfortable around their caretakers. They chose these animals to breed with one another.<\/p>\n After just six generations, the researchers were producing pups that actively sought out interactions with people.<\/p>\n The friendlier foxes also developed features common in domesticated<\/a> animals, including floppy ears<\/a> and shorter snouts.<\/p>\n The scientists also bred a separate group for aggressive behavior. These two groups now let researchers examine what happens when breeding pushes the same species toward opposite temperaments.<\/p>\n Why these cells matter<\/p>\n The team looked at the hypothalamus<\/a>, a small region at the base of the brain. They focused on a part called the ventromedial hypothalamus, which helps control energy use, mothering and other social behavior.<\/p>\n In mice, this area also helps drive aggression<\/a>. Earlier studies had drawn attention to nerve cells there that contain a protein called estrogen receptor alpha.<\/p>\n The protein allows cells to respond to the hormone estrogen. In mouse experiments, researchers used light to switch on cells containing this protein.<\/p>\n \u201cIf you activate them, the mouse will immediately attack another mouse,\u201d Markenscoff-Papadimitriou said. Her team wanted to find out whether friendly and aggressive foxes had different numbers of these cells.<\/p>\n Inside the fox brain<\/p>\n Scientists who run the Russian fox colony sent the team nine brains: three from tame foxes, three from aggressive foxes and three from wild foxes.<\/p>\n The researchers preserved the brains and cut them into very thin slices. They then added glowing labels that attach to particular genetic messages inside cells, helping them identify different types of nerve cells.<\/p>\n \u201cThe tame fox hypothalamus had fewer of these estrogen receptor-expressing neurons, which are known to be part of the aggression circuit,\u201d Markenscoff-Papadimitriou said.<\/p>\n Compared with aggressive foxes, tame foxes had fewer of these cells in the lower, outer part of the ventromedial hypothalamus. <\/p>\n The difference appeared only in a particular subtype that mouse studies have linked to aggressive states.<\/p>\n What remains unclear<\/p>\n The finding does not mean tame foxes have fewer nerve cells throughout their brains. The difference involved one specific type of cell in one small area.<\/p>\n With only three brains from each group, the researchers need more evidence to understand how widely the pattern holds. <\/p>\n They also did not test what these cells do in a living fox, so the evidence connecting them to attacks still comes from mice.<\/p>\n The central question remains unanswered: does having fewer of these cells help make a fox friendly? The change could also be a side effect of something else that breeding altered.<\/p>\n Uncovering the genetic links<\/p>\n Markenscoff-Papadimitriou said the findings could help explain how selective breeding changes brain structure over relatively short periods.<\/p>\n Her team\u2019s next goal is to understand why domestication changes this brain region, which researchers still know little about in foxes. Genes may offer some answers. <\/p>\n Study co-author Anna Kukekova, who studies fox genetics at the University of Illinois Urbana-Champaign<\/a>, may investigate how mutations in different parts of the genome affect the development of these cells.<\/p>\n For now, the findings suggest that breeding foxes for friendliness may have changed more than their behavior. <\/p>\n It may also have reshaped a small part of the brain involved in aggression, offering a new clue to how domestication works.<\/p>\n The study is published in the journal Current Biology<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? 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