Urban red foxes have become more similar to pet dogs as they adapt to the pressures of city life, according to a new study.
Researchers took a look at the difference between the skull shapes of foxes living in cities and those living in the rural countryside to discover that urban foxes have a significantly longer, thinner snout, seemingly perfect for foraging around trash cans and burrowing underneath garden walls.
Reporting their study in the journal Proceedings of the Royal Society B, the team from the University of Glasgow in Scotland studied the skulls of 111 red foxes (Vulpes vulpes) that were collected in London and the surrounding rural boroughs in the early 1970s. Using a combination of imaging and statistical analysis, the team compared the shape and dimension of foxes in different habitats. They also looked at how the skull was affected by sexual dimorphism, the physical difference between males and females of a species.
Along with the narrowing snout, they also noticed the skulls of urban foxes had shrunk in size, which indicates a reduction in brain size and less sexual dimorphism. The team argues this a clear sign of "domestication syndrome," a collection of traits that arise during domestication, including smaller brains, coat color changes, reductions in tooth size, and changes in craniofacial shape.
Effectively, the city foxes were becoming more domesticated just like a pet dog. While it's worth noting that red foxes are still relatively distinct from your pet chihuahua, the researchers argue their findings could provide some hints about how wild dogs eventually became domesticated.
"This could tell us whether the evolution of urban/rural differences was completely unique or something that has potentially happened previously. It turned out that the way urban and rural foxes differed matched up with a pattern of fox evolution that has occurred over millions of years between species,” lead author Dr Kevin Parsons, from the University of Glasgow's Institute of Biodiversity, Animal Health, and Comparative Medicine, explained in a statement.
“While the amount of change isn't as big, this showed that this recent evolutionary change in foxes is dependent upon deep-seated tendencies for how foxes can change. In other words, these changes were not caused by random mutations having random effects the way many might think evolution occurs," Parsons added.
The environment of urban industrialized London has only been around for a couple of centuries, so it might be surprising that foxes have adapted so rapidly. However, as shown by the famous Russian fox experiment, the appearance of domestication can arise in a matter of years or decades. Starting in the 1950s, Soviet fur-farmer-turned-geneticist Dmitry Belyaev and his team spent decades selectively breeding foxes in an attempt to actively domesticate the species. Over numerous generations, Belyaev selected the least aggressive individuals and allowed them to breed together.