Genetic survey of rats could help New York curb the rodent population

"We showed in our paper that related individuals from the same colony stay within a close vicinity of each other over several generations," researcher Matthew Combs said.
By Brooks Hays  |  Dec. 11, 2017 at 11:03 AM
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Dec. 11 (UPI) -- For the first time, scientists are getting a big-picture sense of how rats live, move and interact in New York City. The details lie in their genetic code.

Matthew Combs, a graduate student at Fordham University, has assembled the most comprehensive genomic map yet of New York City's chief rodent. He hopes his work -- detailed most recently in the journal Molecular Ecology -- can help the city's health and sanitation officials curb its rat population.

Over the last two years, Combs has trapped rats all over Manhattan and cut off small portions of their tails for DNA sampling. The results suggest the metropolis is home to two main populations, uptown rats and downtown rats, each with their own genetic signature.

A group's genetic signature is revealed by single-nucleotide polymorphisms, or SNPs -- "a change in a base pair in a certain place in the DNA," Combs told UPI.

"These are mutations that are accumulating randomly throughout the genome," Combs said.

Through random chance, certain mutations accumulate over time as they're passed on from generation to generation.

"Because you get half of your genes from your parents DNA, you have a 50 percent chance of inheriting their mutations," Combs said. "Some [SNPs] get passed on more and more through random chance, and become highly prevalent -- they become like a genetic signature."

This process of random accumulation can only happen through lineages of related rats. As a result, the genetic signatures can reveal gene flow, or the lack there of, across the urban environment.

As Combs' sampling and analysis showed, the SNPs accumulated among uptown rats differs from the mutations amassed in the genome of the downtown population. That's because the two populations are mostly isolated, with very little interbreeding between the two.

Combs was also able to tease out subtler differences in the genetic signatures within each group, revealing the neighborhood-by-neighborhood organization of each rat population.

"We showed in our paper that related individuals from the same colony stay within a close vicinity of each other over several generations," he said. "What that means is that a single colony could be active across an entire city block or several blocks."

The revelation shows rats are organized in ways that mirror human organization. The movement and organization of the population of rats living in the West Village parallels the shape of the neighborhood as defined by humans.

The findings also confirm that infestations are not confined to single properties.

"If you get rid of rats in someone's backyard that might offer some short term relief, but if we know their parents or siblings are next door, we know we're going to see a reintroduction and population rebound," Combs said.

He hopes his work will be used by the city to address infestations within the neighborhood boundaries identified in the new study.

While officials with the New York City Health Department said they've yet to review Combs' findings, several municipal agencies are working together on a rat reduction initiative -- announced by Mayor Bill de Blasio over the summer -- that prioritizes a neighborhood-by-neighborhood approach.

"We've done analysis trying to parse our inspections data to look at the way rats are living and moving in the city," said Caroline Bragdon, director of neighborhood interventions and pest control services for the health department.

Bragdon and scientists working with the city have reached conclusions similar to Combs' findings -- that the city's rats live and organize in neighborhood-like shapes.

As part of the city's rat reduction efforts, researchers have compiled property-by-property rat inspection results to build neighborhood-level infestation maps.

"We use those maps to design programming. Those neighborhoods with greater rat activity get extra resources and assistance, including extermination, cleanup and education and outreach to help property owners improve management," Bragdon said. "We assigned case managers to each neighborhood, to study in-depthly and identify what the factors are that are contributing."

The early findings of case managers suggest neighborhoods with high rat activity would benefit from improved sanitation services -- removing garbage from neighborhoods, public parks, public housing and public schools.

Bragdon said the city will continue to maintain partnerships with academic and research institutions and work with scientists to determine the best strategies for shrinking New York's rat population.

"We are all, for various reasons, interested in where the rats are," she said. "So we share that information back and forth."

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