The evolution of the legendary New York City rat


Rats are the vile creature that occasionally scurried through tunnels alleys and garbage cans.

But in researcher Dr. Jason Munshi-South a lab at Fordham University in New York.

These creatures are a source of evolutionary wonder.

For the past four years researchers have been trapping rats and extracting their DNA to learn more about their evolutionary origins and their interactions with urban environments.

Dr. Munshi- South joins me now.

So we talk about the evolution of rats does a city or a location change a rat?

It can.

The rats originated in Asia but they've spread to cities all over the world.

And cities have some common elements.

But every city is slightly different in terms of the infrastructure that's in place the way the human population density the types of foods that are available.

So Rats do have the opportunity to adapt to local conditions in different cities.

Does that mean that they're essentially evolving over time.

So can we see a difference in rats?

Let's say you studied New York so from the Bronx to Queens to Manhattan?

Within the city you see very subtle differences across the urban landscape between cities you may see more substantial differences as they evolve to face different pressures.

Cities try to tackle this problem all the time especially in places like subways and so forth.

Nice moist dark environments where these guys can run around.

Why haven't we been more successful at eradicating rat populations?

Well there's a couple of different reasons.

One reason is that the rat is exquisitely adapted to reproduce very quickly.

So even if we can reduce the rat population by say 90 percent they can rebound very quickly.

You can have migrants coming from nearby areas and the rest that are still there can breed even faster because they have more access to resources.

The other issue is that we don't really understand the Rat's biology very well in cities.

We've put a lot of effort into trying to kill them but we haven't actually put that much effort into understanding them as a species and understanding their basic biology.

And then there's also a lot of issues that are not particularly scientific but more sociological.

How does a city manage its garbage?

How do individual residents on a property manage their garbage?

How are buildings maintained?

How are subways maintained all of those issues can contribute to rat populations by providing them food and hard bridge places for them to nest and burrow.

Do they cluster?

I mean do they end up or are they communal beings where if we were able to isolate where the communities are we'd have a better chance at eradicating them?

I think that's true they are a colonial species.

So build up a colony you might just have a male female pair first.

They build up their relatives nearby over time as the young disperse and build a nest you know in a burrow right next to their parents and so you will build up this local colony over time.

And one of the things we're doing in New York City is trying to understand how rats are related in different parts of the city with the idea being you can identify that colonial structure how big it is.

And we found that in general it spans a few city blocks maybe up to four or five city blocks.

So if you could address rat control on that scale you'd have a much better chance of reducing the population long term.

So they're uptown rats versus downtown rats?

That was one of the things we found surprising we found that rats in general.

You see it north to south kind of a gradient of relatedness where the closer they are the more related they are.

There seems to be this split in midtown where you have uptown rats that are more related to each other than they are to downtown rats.

And we think it's because Midtown is kind of a barrier for them not a physical barrier like a mountain range but more of a habitat barrier.

The buildings here are better maintained.

There's less garbage.

There are fewer apartment buildings and restaurants and more office buildings.

So it's kind of a no go zone for rats and so even that minor barrier is causing the uptown and downtown rats in Manhattan to diverge from one another.

How did they get here in the first place?

We did a study where we asked researchers from all around the world to send us rat samples so we received tale's livers ears from cats all over kind of the worst mail you could receive.

But we were able extract DNA from all those samples and trace the patterns of the relationships between all of these rat populations in New York City is firmly related to rats from Great Britain and possibly a few other Western European nations like France.

And that's really not that surprising given that the historic record suggests they arrived here around the Revolutionary War maybe a little bit before and since this was a city controlled by the British it was basically part of the British colony.

It's not surprising that they brought the rats over.

Why should we care about the genetic backgrounds of rat?

I mean you and your team are working so hard about this when you discover what it is that you're looking for.

How does that help us all?

Well for us you know there's definitely just a basic scientific interest.

It's a great system for understanding evolution because you have a species the same species that was introduced to so many different places that allows you to it's almost like a natural experiment where you can see play out multiple times in different cities.

But there's also this applied angle.

Rats are one of the worst invasive species one of the worst pests around the world.

They destroy food supplies they destroy infrastructure.

They spread disease so we can understand their biology better where they came from and how their populations are structured.

We can design better strategies for reducing their populations.

Dr. Jason Munshi-South of Fordham University.

Thanks so much.

Thank you.

My pleasure.