The Genetic Divide Between NYC's Uptown And Downtown Rats

Nov 30, 2017
Originally published on December 1, 2017 9:36 am

The Empire State building, pizza and Broadway are just a few things synonymous with New York City — and then there's the rats.

Like many other major metropolitan areas, New York City has a rat problem. But that doesn't mean that all the rats are the same.

Matthew Combs is a graduate student at Fordham University who studies rats. In a recently published paper of his, Combs shared his findings about the genetics of the city's brown rats.

"Despite the fact that rats live right in our cities and under our feet, under our noses, there's actually quite little knowledge about how they behave in the cities, how they move around," Combs says.

And that lack of knowledge is a problem, just like the vermin themselves.

"They are a serious public health threat," he says. "They carry several zoonotic diseases that we are worried about. So the more we know about how they move, how these colonies interact, the better we can create management strategies to stop them."

Combs and other researchers spent two years going around the city and trapping rats. After extracting and analyzing their DNA, he determined that the rats that live in uptown, north of 59th Street, are distinct from those living in downtown, south of 14th Street. The Midtown area is more sparsely populated — by rats, anyway — presenting a barrier to genetic mixing.

Much like people, New York City's rats have their own home areas and generally stick to those neighborhoods, the study found.

"We know that related rats, rats in the same colony, tend to stay within about 200 to 400 meters of each other, even over multiple generations," Combs says. "That tells us that most rats actually stay right very close to where they were born."

While a majority of the rats stick to their home turf, Combs says about five percent do leave their colonies and go to different blocks, parks or even farther — up to 2,000 meters. It's those rats, he says, that present the biggest problem.

"Those are the rats — those dispersing rats — that can actually move genetic information and move even their pathogens, and lead to that spread of disease and that gene flow we detected," Combs says.

While it may seem like it is good news that these rats generally stay in the same area, Combs says it's not that easy of a matter.

"It's not a good thing if your neighbor has rats, because it means that you have rats as well," he says. "That's not quite in line with the way that we deal with rats."

Combs says that in New York if a person has rats, it's the property owner who has to deal with them, but really it's a community scale issue and should be dealt with that way. He's hoping that his research can change how rats are dealt with.

As for his personal feelings about rats, Combs says the pests are more complex than they seem.

"The more I learn and the more I read about rats, I think the more I'm able to respect them," he says. "I mean, they're remarkable creatures — they're able to change their movement patterns based on the things humans do, so they're very smart. They're also very social creatures."

But they're still the creatures that can steal an entire slice of pizza. (Or can be trained to, anyway.)

Copyright 2017 NPR. To see more, visit http://www.npr.org/.

KELLY MCEVERS, HOST:

In New York City there's an old thing about whether you are an uptown person or a downtown person. Turns out this also applies to rats. Matthew Combs is a graduate student at Fordham University who studies rats. He has just published a paper about the genetics of brown rats in New York, and he's with us now. Welcome.

MATTHEW COMBS: Thank you.

MCEVERS: So when we think about people researching rats, I think a lot of us imagine, you know, these little fluffy lab rats. But you study New York City rats, which I would imagine is a very different type of rat. Can you explain why you're interested in them?

COMBS: Sure. So despite the fact that rats live right in our cities and under our feet, under our noses, there's actually quite little knowledge about how they behave in cities, how they move around. They are a serious public health threat. They carry several zoonotic diseases that we are worried about. So the more we know about how they move, how these colonies interact, the better we can create management strategies to stop them.

MCEVERS: So tell us about this latest study. How did you determine that there are uptown rats and downtown rats?

COMBS: Sure. So we spent about two years collecting rats all over the city, trapping them ourselves. Once we did that, we would take a sample back to the lab and extract DNA. And from that DNA we looked at thousands of little genetic changes to see who was more related to whom. And we realized that there were two pretty unique clusters of rats, those uptown rats and downtown rats. And we were able to analyze that with a few separate analyses.

MCEVERS: So what do we know now that you've done your study?

COMBS: Sure. So we know that related rats, rats in the same colony, tend to stay within about 200 to 400 meters of each other even over multiple generations. So that tells us that most rats actually stay right very close to where they were born. But we do know that a small number, maybe 5 percent or so, actually leave their colony and jump maybe across the block, across the park, or sometimes even further up to a couple kilometers. And those are the rats, those dispersing rats, that can actually move genetic information and move even their pathogens and lead to that spread of disease and that gene flow that we detected.

MCEVERS: Oh, OK. So it sounds like the fact that rats are staying within these small areas, like, a couple - it's basically like a couple big New York City blocks - is a good thing.

COMBS: Yeah, it is a good thing. It's not a good thing if your neighbor has rats because it means that you have rats as well. That's not quite in line with the way that we deal with rats. Most often in the city if a person who owns a property has rats they receive a fine. They're told to deal with it. But it turns out that it's really a problem more on a community scale, more on the scale of an entire block. So we're hoping that with this information we can change how we deal with rats and maybe expand the scope at which we are trying to control them.

MCEVERS: OK. Have your thoughts about rats changed since you did this research?

COMBS: Yeah. The more I learn and the more I read about rats, I think the more I'm able to respect them. I mean, they're remarkable creatures. They're able to change their movement patterns based on the things humans do. So they're very smart. They're also very social creatures. So things like that have shocked me.

MCEVERS: So you have more respect for them?

COMBS: Absolutely.

MCEVERS: Fordham University graduate student Matthew Combs, thank you so much.

COMBS: Absolutely.

(SOUNDBITE OF LAPTOP INSTRUMENTAL'S "UPTOWN GIRL") Transcript provided by NPR, Copyright NPR.