Although no one’s quite sure how many there are, estimates of the number of rats in New York City range from a quarter of a million to somewhere near the 2 million mark. Either way, that’s far more than most people would be comfortable with.
Many view these critters as a monolithic, writhing mass of squeak-emitting filth bags; disease-carrying rodents and nothing more. However, a new study in the journal Molecular Ecology has found that there are two distinct genetic varieties in Manhattan: Uptown and Downtown rats.
The extensive research project, conducted by Fordham University and Providence College, involved scooting around the famous concrete jungle, capturing rats, and cutting off a little piece of their tails or taking a skin sample. Using this library of 262 severed rat segments, the team assessed their genomes and came to their aforementioned conclusion.
Manhattan’s brown rats, which likely first invaded the city from Great Britain (and possibly France) back in the 1700s, are split into two different “evolutionary clusters”, as per the authors’ paper. This doesn’t mean that they are separate species – an Uptown and Downtown pair could still produce viable offspring, for example – but it does suggest they have kept to themselves for some time now.
Even within these two subsets of brown rat, there were smaller genetic “islands” to be discovered. “Within the Uptown cluster, rats in Upper Manhattan and the northern portion of Harlem West and Harlem Central were differentiated from those in the Upper West, Upper East, and Harlem East,” the team explain.
Still, the big finding here is the split between Uptown and Downtown. So what’s the cause of this rat snobbery?
Something is clearly causing a reduction in the flow of genes across Midtown. The team suspect that there are probably less rats in that section overall because it’s not as comfortable for these donut, avocado, and (of course) pizza-wielding vermin to inhabit.
“Every neighborhood in Manhattan supports the presence of rats to some degree,” but “Midtown is largely a center of commerce and tourism,” the paper notes. There’s less food waste there, less suitable shelter, and “increased levels of disturbance.” Pest control there may also be more prominent.
All in all, this is creating a barrier to immigration from Uptown to Downtown, and vice versa – hence the two evolutionary clusters of brown rats.
Widespread genetic analyses are rather marvelous at completely revolutionizing our understanding of animals we take for granted. Now, thanks to this novel study, we know the reputation of New York City as a diverse, cosmopolitan metropolis doesn’t just apply to its human residents.