What Happens When Urban Rodents Take on a Human Diet?

In 2015, a video of a rat carrying an entire slice of pizza down the stairs into a New York City (NYC) Subway station went viral. Apparently, this type of diet for NYC rodents shouldn’t be all that surprising. A recent study from the City University of New York (CUNY) and Fordham University shows that unhealthy human eating habits may be responsible for an evolutionary adaptation in NYC rodents.

The study suggests the change in these urban rodents likely stemmed from their primary consumption of human food waste, much of which consists of — you guessed it — fast food. It looks like even rodents have a hard time metabolizing the likes of McDonald’s, Taco Bell and Burger King.

THE STUDY. Researchers Stephen Harris and Jason Munshi-South conducted the study, titled “Local adaptation in urban white-footed mice.” The study examined the diet of 48 white-footed mice — which are native to North America — from three NYC parks and three rural areas. Harris and Munshi-South tested specifically for genetic variances in the mice genome structures and discovered 381 differences. They focused on 19 of these genetic variations, many of which perform the role of metabolizing lipids and carbohydrates.

“What we found was there were these mutations and signatures of evolution occurring in many genes that had to do with metabolism and the breakdown of fats from high-fat diets,” Harris told PCT. He added that this link then led them to believe the genetic differences originated from something urban mice were eating that rural mice were not.

In the urban mice, evidence showed the genetic differences possibly originated from fatty liver disease, which is “a major hallmark of obesity and diabetes,” according to the study. In humans, and now urban rodents, these health issues are caused by an increased consumption of foods high in fats and carbohydrates.

EVOLVING. The takeaway from this study, Harris said, was how such a small area could contain a large amount of genetically different mice.

“Usually what you would find is over hundreds of kilometers, these mice are just one population,” said Harris. “We were finding that over one or two kilometers, the Manhattan mice were genetically distinct populations from the Queens mice.”

The study ultimately suggests that these city mice could be evolving in response to what food source is available to them, which is mainly unhealthy human food waste on NYC streets. Unlike humans, however, Harris said this high-fat diet is not necessarily bad for these native urban rodents.

“I think it’s more of just a response to the environment,” Harris said. “I don’t think it’s affecting them positively or negatively in any meaningful way. It’s more of understanding what happens when humans come in, pick a spot and turn it into a city. How do the native animals respond?”

WHAT’S NEXT? Harris said one main question their future research will try to answer is whether this genetic phenomenon is indicative of all urban environments, an “urban syndrome,” as Harris calls it.

“This could be an extreme case of local adaption,” Harris said. “And New York City is a special case because it is so densely populated. Central Park is completely shut off on all sides by streets and sidewalks.”

Harris is currently working with a new lab at the State University of New York (SUNY) Purchase College and studying various urban species to see if this “urban syndrome” exists.

“I would like to generally look more at these urban adapters,” said Harris. “Not pigeons, rats, cockroaches — things that travel with humans. I’d like to expand it out and look at urban adapters, native animals that also happen to do well in an urban setting.”

The author is an Ohio-based writer. She can be contacted at ksondereker@gie.net.