New York's REAL ratpacks revealed: DNA study finds uptown and downtown rodents have different genes

  • Uptown Manhattan rats were found to be genetically distinct to Downtown rats
  • Even different neighborhoods like the East and West Village had distinct rats
  • Rats don't move farther than 1,400 meters (4593 feet) away from their colonies
  • This information could be useful for New York City pest managers, as they could focus on eradicating rat units of this size to limit reinvasion by rats that disperse

New York's rats are genetically distinct, possessing distinct DNA patterns depending on where they live, a new study has revealed.

The study involved sequencing the DNA of trapped Manhattan rats and mapping their genetic profiles.?

Uptown rats were found to be genetically distinct to Downtown rats, and even different neighborhoods like the East and West Village had their own distinct rat populations.??

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Left: Map of Manhattan showing two genetically distinct clusters of Uptown (black, north of 59th street) and Downtown (white, south of 14th street) rats. D: Estimated migration rates of rats in Manhattan

Left: Map of Manhattan showing two genetically distinct clusters of Uptown (black, north of 59th street) and Downtown (white, south of 14th street) rats. D: Estimated migration rates of rats in Manhattan

Midtown Manhattan, however, did not have its own genetically distinct population, likely because the area is less residential and so has fewer household trash sources.

The ultimate goal of the study was to help manage New York City's rat problem as they can spread disease, and some?estimates?place the city's rat numbers at 2 million - about 20 per cent of New York's 8.4 million human population.?

The new?study, led by Fordham University graduate student Matthew Combs, involved studying brown rats (Rattus norvegicus) across the island of Manhattan in New York City.?

According to the researchers, rats likely invaded the southern trip of Manhattan between 1750 and 1770 , after being introduced by Europeans crossing on ships.?

WHAT THE RESEARCHERS FOUND?

To learn more about the genetic profiles of New York City rats, researchers based at Fordham University trapped rats in various locations in Manhattan.

They used lethal traps and collected tail tissue samples of the rats to sequence their DNA.?

The researchers also recorded where the rats were caught, and information about their location, sex, weight and sexual maturity.?

They collected 393 samples overall, of which 288 were chosen for sequencing that maximized geographic coverage.

The results of the study revealed a clear split between Uptown and Downtown genetic groups.

The results also showed that rats don't tend to move farther than 1,400 meters (4593 feet) away from their colonies.?

This information could be useful for New York City pest managers, as they could focus on aiming to eradicate rat units of this size to limit reinvasion by rats that disperse themselves.?

Top row: Spatial genetic clustering within only the Uptown rats identified in the full landscape analysis. Bottom row: Spatial genetic clustering within only the Downtown rats identified in the full island analysis

Top row: Spatial genetic clustering within only the Uptown rats identified in the full landscape analysis. Bottom row: Spatial genetic clustering within only the Downtown rats identified in the full island analysis

A recent survey conducted by the NYC Department of Health and Mental Hygiene (DOHMH) found that 8.2 per cent of all properties in Manhattan showed signs of rat activity, but brown rats also lives in sewers, subway tunnels and parks.

For the study, the researchers divided Manhattan into three areas: Downtown (from the southern tip to 14th street), which has a mix of residential, commercial and office spaces; Midtown, between 14th and 59th street and has higher levels of office and commercial spaces, transportation hubs and less residents; Uptown, which extend from 59th street to the northern tip of Manhattan and is mostly residential.?

Researchers used lethal snap traps baited with a mixture of peanut butter, oats and bacon to attract the rats. For every trapped rat, the researchers cut 3-4 cm of tail tissue and stored it in alcohol,  recording the location, sex, weight and sexual maturity of the rat

Researchers used lethal snap traps baited with a mixture of peanut butter, oats and bacon to attract the rats. For every trapped rat, the researchers cut 3-4 cm of tail tissue and stored it in alcohol, recording the location, sex, weight and sexual maturity of the rat

Manhattan is further divided into 12 community board districts, which the researchers also used.?

Rats often burrow in earthen spaces, so the researchers samples rats in parks as well as private properties, with permission.?

Sampling map for the rats trapped in Manhattan, NYC. Red points are locations of rat samples. The island is separated into 12 community board districts

Sampling map for the rats trapped in Manhattan, NYC. Red points are locations of rat samples. The island is separated into 12 community board districts

They used lethal snap traps baited with a mixture of peanut butter, oats and bacon to attract the rats, setting them for 24-hour periods.?

For every trapped rat, the researchers cut 3-4 cm of tail tissue and stored it in alcohol, and also recorded the location, sex, weight and sexual maturity of the rat.?

The researchers spent over a year and a half trapping and sampling the rats.

Between June 2014 and December 2015, they collected 393 samples, of which 288 were chosen for sequencing that maximized geographic coverage.?

The researchers then sequenced the DNA of all the rats, and generated a matrix of average genetic dissimilarity based on genetic variations between the samples.?

The results of the study revealed a clear split between Uptown and Downtown genetic groups.?

Midtown rats showed higher levels of inbreeding and reduced gene flow.?

The results also showed that rats don't tend to move farther than 1,400 meters (4593 feet) away from their colonies.?

This information could be useful for New York City pest managers, as they could focus on eradicating rat units of this size to limit reinvasion by rats that disperse.

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