A new study has revealed that New York's rats are genetically distinct, possessing distinct DNA patterns depending on where they live. The discovery was made after the DNA of trapped Manhattan rats was sequenced and mapped based on their genetic profiles.
Funny enough, the 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. However, Midtown Manhattan did not have its own genetically distinct population, likely because the area is less residential and so has fewer household trash sources.
The study intended 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 percent of New York's 8.4 million human population.
Fordham University graduate student Matthew Combs, was led by the study to take a closer look at 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.
Researchers based at Fordham University trapped rats in various locations in Manhattan so as to learn more about the genetic profiles of New York City rats. They used lethal traps and collected tail tissue samples of the rats to sequence their DNA.
They gathered data on where the rats were caught, and information about their location, sex, weight and sexual maturity. A total of 393 samples were collected overall, of which 288 were chosen for sequencing that maximized geographic coverage.
Results revealed a clear split between Uptown and Downtown genetic groups. It 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.
The researchers 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.
They 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.
They then sequenced the DNA of all the rats and generated a matrix of average genetic dissimilarity based on genetic variations between the samples. Results indicated that there’s a clear split between Uptown and Downtown genetic groups.