Urban red foxes are becoming more similar to domesticated dogs as they adapt to their city environment, according to a new analysis.
"A team led by Dr Kevin Parsons, of the University of Glasgow’s Institute of Biodiversity, Animal Health and Comparative Medicine, has carried out an analysis into the differences between urban and rural red foxes in the UK.
Their findings go some way to explaining how dogs could have evolved into our current pets.
With our current lockdown measures due to the covid-19 pandemic we are seeing a number of animals more frequently in our cities. It has been known for some time that cities create new habitats for wild populations. While many can’t cope, it is recognised that some types of animals are especially good at living within cities. Red foxes are prevalent within several cities within the UK and elsewhere where they have become well-established.
“We wondered whether this change in lifestyle was related to adaptive differences between urban and rural populations of red foxes. We assessed skulls from hundreds of foxes found within London and the surrounding countryside and saw that urban foxes had a smaller brain size capacity but also a different snout shape that would help them forage within urban habitats. There was also less of a difference between males and females in urban foxes,” said Dr Parsons.
These changes matched up with what would be expected during a domestication process. In other words, while urban foxes are certainly not domesticated, they are changing in ways that move them closer to what is seen in many domesticated animals.
“This is important because human-animal interactions are continuous and some of the basic environmental aspects that may have occurred during the initial phases of domestication for our current pets, like dogs and cats, were probably similar to the conditions in which our urban foxes and other urban animals are living today. So, adapting to life around humans actually primes some animals for domestication, added study co-author Dr. Andrew Kitchener from National Museums Scotland.
The researchers from the Universities of Bristol, Edinburgh and Massachusetts and National Museums Scotland, then decided to test whether differences found between urban and rural red foxes had any similarity to what is found across different species of foxes.
“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. 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,” said Dr Parsons.
The team’s research paper, Skull morphology diverges between urban and rural populations of red foxes mirroring patterns of domestication and macroevolution, is published in the Proceedings of the Royal Society Series B."
Hypothesis questioned in North America
"As foxes move from the forest to the city, they show more doglike traits and appear to be naturally self-domesticating in the U.K. — but the same isn’t happening here at home...
Foxes in Canada are not showing domestication syndrome like U.K. foxes are, and Parsons says there could be many reasons to explain why this is the case including that the foxes in Canada and the U.K. come from a different lineage and may not evolve the same way.
Population density may also play a role: Toronto has a lot of open space compared to Glasgow, meaning foxes can be timid and find hiding places more easily in a Canadian city. The cities in the U.K. also have more of an abrupt end compared to Canada, he adds.
“In Canada, you drive an hour and it’s sprawled out with suburbs. So, getting access to the centre of the city takes much longer,” he says. “Here, I live in the suburbs but in five minutes I’m in the core of Glasgow. Then, a five minute drive the other way takes me into cow fields and countryside.”
There’s no study that looks at domestication syndrome in Canadian foxes, at least to Danielle Fraser’s knowledge.
“Something I thought would be an interesting extension to this study is looking at populations from other urban and rural pairs throughout the range of modern foxes,” says Fraser, an evolutionary biologist and research scientist at the Canadian Museum of Nature.
Pointing to how the snouts of urban foxes got shorter in the study, Fraser adds that previous studies have shown canines being more prone to evolvability in the face, particularly the snout, than other parts of their skull. "
© Nicole Watson/Can Geo Photo Club
More information on foxes and skull changes due to domestication, see also;
"Researchers have discovered that what makes for a beautiful face in a fox, is similar to the features of an attractive human. The study found that features seen in farmed foxes - such as flat faces and smaller jaws, as well as a large space between the height of the cranium and face - are the same features that humans find desirable. According to Dr Elia, the link is hormonal and estradiol and serotonin, which regulate behaviour, also dictate some aspects of development"
"Selective breeding of the red fox (Vulpes vulpes) is focused on genetic upgrading of economically important traits, i.e. those determining the quality and volume of the final product – the fox pelt. Long-term artificial selection targeting traits related to coat quality, animal size, pelt length and fertility has led to the increasing differences in terms of the exterior, body dimensions, behaviour and physiology between the farmed foxes and their wild ancestors. Over time, farm foxes have become markedly bigger and heavier, while at the same time the weight of certain internal organs – e.g. the liver, spleen and kidneys – has increased considerably. Wild canids exhibit marked differences in the morphology of both sexes (particularly the skull and dentition). In farm foxes sexual dimorphism has been greatly reduced, which is an evident effect of domestication. A reduced brain size of animals kept in captivity is also considered to be one of the effects of domestication. Such rapid changes in the body structure and proportions, taking place within slightly over 100 years of red fox farm breeding, have resulted from the relatively high heritability of the traits under genetic improvement and the application of artificial insemination in the reproduction of these animals. Moreover, currently bred farm animals (including the red fox) originate from relatively small founder populations, which were subjected to great selection pressure.
The results of the phylogenetic and phylogeographic studies suggest that when we compare the wild population of European red foxes with farm-bred red foxes, in fact we compare two genetically distinct populations – the Eurasian red fox population vs. the red foxes of North American origin (a founder population of farm foxes which genetic structure has been changed through selective breeding). Thus, the morphological differences between wild and farm-bred foxes may have been brought about not only by intensive artificial selection of captive foxes but also by distinct gene pools of both populations.
The main goal of the project is to elucidate to what extent the phenotypic differences between two compared groups of red foxes are determined by different genetic structures of wild and farm-bred populations." - Heliodor Wierzbicki
https://www.researchgate.net/publication/351090025_Insight_into_the_Genetic_Population_Structure_of_Wild_Red_Foxes_in_Poland_Reveals_Low_Risk_of_Genetic_Introgression_from_Escaped_Farm_Red_Foxes
@Terry Hooper Agreed, there is much to consider. The melanism increase may not be down to hybridisation alone, or at all (we need to genotype such foxes to know), but it might also be due to climate change and industrialization, as with the peppered Moth. Melanistic foxes - which are bolder than their red counterparts due to their melanism alone - may be more prone to take an interest in humans and what we have to offer, making them more prone to being habituated and thus more self-domesticated also ("asking" for food and being "friendly" with the humans that share their territory). Then there is the fact our "old foxes" may have had a melanistic type (the "crucigera "cross" Latin name for our native species confuses me with foxes today, but maybe there was a native type similar to those cross foxes in the US once?)
Actually having a conversation with a friend today about how humanity is sort of blind to the domestication occurring among wildlife 'in situ' and how birds have evolved towards bird feeders here, instead of native or even introduced plants. I think planting native, to support wildlife, and giving it a space to safely remain "wild" is the best thing wildlife supporters can do.
There are some good points but I would like to play "Devil's Advocate". Firstly, regarding the muzzle length this may not be due to the fox adapting but down to the type of fox studied. Our Old Foxes were wiped out by the 19th century and later "Hill foxes" show the traits of red foxes not the overall, uniform colour of previous times. Thousands of foxes were imported from around Europe and possibly shipped from further afield. I have looked particularly at the heads of hundreds of foxes now and differences do stick out like a sore thumb. I think that shorter or longer muzzles are down to where the foxes ancestors came from. We know that rescues from certain areas pick up and care for foxes before releasing them in "fox friendly" areas. The rescues refuse to help or cooperate on this subject so we have to assume that most foxes they rescue are from a certain region they cover. You keep taking foxes from that geographical area and disperse them in areas further afield then traits carried in their lineage will show up and they will bred with local foxes and so a trait continues on. Most academics have no idea this is going on and that it would throw off the results of the work they carry on.
Second point to be devilish: lack of urban foxes in Canadian suburbs. A lot of people in the UK have no idea that foxes visit their gardens or that there is even a den just beyond their fenceline. In the United States and Canada most people have no idea that they have coyotes visit their yard, streets or parks. A fox is smaller than a coyote and as we all know if a fox does not want you to see it then you won't. One fox spotted in a U.S. suburb created local TV, radio and newspaper headlines because "THERE IS A FOX IN THE CITY!!" Had that one person not seen the fox under a tree and taken a photo no one would be any the wiser. Using triple cameras in the past I have noted foxes checking out cameras and attempting to avoid tripping them so unless one is not bothered by the IR light you are not going to get a photo. Really, before you can say foxes are NOT in a city you need to do camera work for a long time. I did laugh when I read about it being further from countryside in Calgary than Glasgow is....Foxes live in cities including NY and so long as there is food and no major threat they carry on living in cities -parks, drains, gardens, derelict or empty buildings -foxes adapt and find habitat. There are accounts of foxes with dens in farmers yards, in barn walls and so on in the 19th century AND that in "fox hunting country" and no one knew.
The other problem is that in the U.S. or Canada it is far more likely that a fox seen in a garden might be shot -same for coyotes. That or the grubby pest controllers get in and take the money to "eliminate the threat".
Humans HAVE habituated foxes and they have also habituated badgers not to mention hedgehogs -all three were formally killed out of hand for bounties (hedgehogs just in case they came across a game birds egg and might eat it). It's a very complex subject but habituation has taken place and unless people stop trying to hand feed or cuddle up to foxes it will continue. Foxes knowing people are friendly do become semi domesticated and therein lies a problem when someone who is anti fox has one walk into their kitchen.
I think that one reason they have not seen the same in North America is because a high percentage of North American red foxes are lineages of feral farmed foxes, which may already possess these adapted traits prior to feralization. The native species of fox are so few in number, one subspecies is now listed as endangered. They also do not have the density of foxes and humans per square mile as we do, where habituation over generations is more likely.
I also think it is possible, in London and Halifax especially, that feral farm foxes may have contributed to fox population genetics and that it might also be one reason we are seeing such traits - on top of the consistent generational habituation, as London was the fur capital of the world at one point, with several fox farms and furriers listed as being in the city pre world war II (when rationing and fox farmers being called up for service saw the release of stock into the countryside). Another indicator of this possibility is the high rate of melanism in both London and Halifax fox populations.