A new study suggests that mice in New York are evolving to be better able to digest fast food.
The researchers behind the study believe that our habits of dropping fast food for mice to eat is changing their biology.
Study into genes
If you have a food job in a city, you have probably come into contact with a mouse on at least one occasion. Along with similar rodent species, they can be a real scourge in restaurants and other food preparation areas, coming in search of food to eat. They often eat the food dropped by humans in the streets, left in bins, and even stored inside if they can get to it.
Researchers Stephen Harris, from the State University of New York, and Jason Munshi-South, of Fordham University in New York City, questioned whether diets in the city might be changing the digestive systems of mice. These mice live amongst us and often eat our discarded food, so, they reasoned, might city mice be evolving in a different direction to their rural counterparts?
In order to explore this idea, they captured 48 white-footed mice (known as Peromyscus leucopus) in the parks of New York, as well as from rural areas nearby. All of the mice were native to the New York State, and so they should theoretically all share the same exact physiology. But, the pair posited, it could be that city mice had begun to adapt for city living.
They looked at the RNA of the mice to see if different genes could be found in the different mice. There were 19 single nucleotide polymorphisms (SNPs) that they decided to focus on – these are places in the genome where just a single letter might change from mouse to mouse, meaning they show the subtle differences. Several of them were associated with digestion and similar processes, such as producing omega-3 and omega-6 fatty acids, something that developed when humans moved into agriculture for the first time.
Channelling pizza rat
The study puts many in mind of the famous pizza rat, a rat who went viral after he was filmed carrying an entire slice of pizza down some stairs – the slice being larger than his own body. This will be of interest to those in environmental food jobs, who want to know how our food production affects the world around us.
Some of the genes highlighted were linked to non-alcoholic fatty liver disease, which can be caused by eating too many fatty acids – such as you might find in fast food.
“The first thing that we thought of was the ‘cheeseburger hypothesis’: urban mice subsidising their diet on human food waste,” says Harris. The hypothesis seems to be borne out by the fact that the city mice had larger livers which exhibited more scar tissue.
Ultimately, the sample size was too small for exact results to be gained, but it’s certainly a very interesting start which reveals the changes could be real. City mice do also have a great deal of access to foods like seeds, nuts, and berries in parks, so they likely eat an eclectic diet which encompasses fast food as well as more normal mouse diets.
The next step for this study will be examining the genes more closely to see if they have any effect on the fitness or the mating selection of the mice, and whether they are being passed down successfully, as well as taking larger sample sizes.
Hopi Hoekstra at Harvard University says the study, “provides us with a really cool way to study evolutionary change, sort of as it’s happening.”