By Janet Faller Sassi, Editor & Associate Director for Internal Communications, Fordham University
For New Yorkers, it’s hard to imagine urban rats as anything but revolting. There they are, circling garbage bins at the end of the subway platform during rush hour, astonishingly bold—and large.
But to Jason Munshi-South, Fordham University associate professor of biology, they’re a species whose mysterious past and intriguing patterns of movement around the city make them ripe for research.
“We’ve put a lot of effort into trying to kill urban rats,” says Munshi-South. “But we haven’t really put that much effort into understanding them as a biological species.”
Munshi-South and his team have received $670,000 from the National Science Foundation to study the evolution and ecology of New York’s rat population, specifically, how it survives and evolves within a complex environment. Working out of a laboratory at Fordham’s Calder Biological Field Station in Armonk, New York, he and his team have collected rat DNA from every one of the 40-something zip codes in Manhattan. The team, which includes doctoral student Matthew Combs, began collecting samples from Manhattan rats in 2014.
Through genetic analysis, the team has been able to construct spatial models of how the rats move around the vast networks of Manhattan’s parks, streets, sewers and subway systems. And, not unlike human New Yorkers, research shows that the rats tend to move more fluidly on a north-south axis, with more difficulty in getting “cross-town.” (Midtown, with its massive office buildings and better overall maintenance, makes it a bit of a “no-go” zone for rats.)
“There are definitely uptown rats and downtown rats,” says Combs, who does most of the collecting using enclosed plastic traps baited with peanut butter and bacon.
Although all New York City rats are of the Norway (or “Brown”) rat variety, there are minute genetic differences even among the New York City populations. As they tend to colonize, their “communities” generally span a few city blocks, Munshi-South says. And they’re fiercely tribal. “We think that once rats get established and build big, healthy colonies, it’s hard for new rats to integrate and breed into the population.”
The biologist first developed his passion for rats when he observed that they rarely chose green spaces for their urban habitat, like white-footed mice, squirrels and other rodents. And, yet, they seemed to be “everywhere else in the city.”
“So I became interested, then, in how rats move and spread their genes in the built environment.”
The team’s grant funding is also being used to track the historic movement of rats across the globe. So far, they have collected and sequenced rat DNA from 30 countries, and have generated genomic data that traces the rat lineage from the areas of Mongolia and Northern China. The rats reached Europe in the 1500s and, from there, moved to America around 1750. New York City rats, therefore, are closely related genetically to Western European rats, most likely from Great Britain or France.
Munshi-South and his team’s research has been widely disseminated. Their large-scale genomic analysis of brown rats around the world, the very first ever done, was published last year in the Royal Society’s flagship journal, Proceedings B. The paper was written up in The New York Times by science writer Carl Zimmer. An additional paper by Munshi-South and co-author Marc T.J. Johnson was published this month in the journal Science, in which the researchers cite direct evidence of evolutionary change among more than 100 species living in cities around the world. And in December, Munshi-South will appear in an interview done by PBS correspondent Hari Sreenivasan for a segment on SciTech Now.
But academic papers are not the only byproduct of Munshi-South’s studies. The research is of interest to New York City’s Department of Health, which is working with him to determine the locations of the city’s largest clusters of rat populations. Besides being a symbol of urban decay, New York City’s estimated million-plus rats destroy infrastructure and spread diseases such as salmonella and leptospirosis. “If we can successfully model how rats move around the city and where their largest colonies are, we can better control their populations—or modify the landscape to change their behavior,” says Munshi-South.
Even so, living with city rats is a likely inevitability as they remain extremely adaptable, he says. “You can really never get rid of them, and almost certainly they will outlast humans on the deeper evolutionary time scale.”