Oh, Rats!

In disease research, rats have the lamentable circumstance of being poked and prodded as a test subject. Today I am turning the tables to look at rats in a different way – by reading the literature on the evolutionary biology of rats and mice.

Mouse photo from Flickr. By Kathryn [CC BY-ND 2.0].

A study performed by Fordham University on brown rats in New York City revealed a close genetic linkage to Western Europe. Additionally, uptown rats had distinct genetic structures & clustering when compared to downtown rats. They can be further categorized into specific rat neighborhoods. Rats tend to stay within 30-40 meters of their home but can travel hundreds of meters to find a mate.

A paper published in Molecular Ecology on white-footed mice in the Big Apple found that different mice populations within the city can be categorized by their locations. It was also discovered that the mice populations diverged genetically within the last century (Munshi-South & Kharchenko 2010).

Photo by Burst on Pexels.com

There is disagreement in the literature surrounding the genetic diversity of white-footed mice. Depending on the genetic markers that evolutionary biologists use to determine diversity, separate conclusions may be reached. One study from Evolutionary Applications open access journal arrived at the determination that mice populations within the city had lower genetic variation than those in nearby suburban or rural areas. Central Park was listed as an exception to that rule, containing “one of the most isolated and unique NYC populations, along with Fort Tilden and Jamaica Bay” (Munshi-South, Zolnik, and Harris 2016).

So, it appears as though urbanization caused physical separation, and later on genetic separation of white mice populations throughout NYC. Urbanization can act as a selection pressure for many species, preventing individuals with certain traits from passing on their DNA and allowing others to prevail regardless of whether or not those traits are truly advantageous to their fitness. One example of this last point is the peppered moth.

peppered moth
“Peppered moth” by David Short on Flickr [CC by 2.0].
Maybe you’ve heard of the peppered moth before in a biology class? There are two versions of the peppered moth: black and white. It’s a testament to natural selection because during the Industrial Revolution, black moths were more likely to blend in with their surroundings, while white moths were more likely to get eaten and not pass on their DNA. It appeared as though moths were suddenly becoming black, but the truth was that white ones just weren’t surviving. This story is also relevant in regards to urbanization as a selection pressure. Some survivors, like rats and black moths, aren’t necessarily the “fittest” but they survive because it works in that environment.

close up photography of coral reef
Photo by Flickr on Pexels.com

Did you know that non-native island rats can have a negative impact on coral reefs? Perhaps the most interesting rat study was one published in Global Ecology and Conservation regarding this exact predicament. Rats are opportunistic feeders that have been known to eat anything from crabs and baby turtles to sandalwood fruit and even bird eggs. When rats eat bird eggs and kill vegetarian crabs, birds can no longer drop guano in shallow water near the reef. As a result, those nutrients cease to benefit fish or corals. Additionally, crabs won’t be able to minimize vegetation growth along the shore and bird habitat will be replaced with trees which aren’t ideal for nesting.

The study goes into depth on which species are impacted by island rats, whether indirectly or directly, but also points out the fact that some species have already gone extinct because of this issue.

beautiful sky
Photo by João Jesus on Pexels.com

“Pre-European losses may exceed 2000 species and are principally of rails, pigeons, doves, parrots and passerines, mainly due to predation by non-native mammals—primarily rats, along with the dogs and pigs brought by Polynesians and hunting by humans themselves.” Harper & Bunbury, 2015

Although it’s pretty difficult to exterminate non-native island rats, a suggested solution for increasing genetic diversity in populations of white-footed mice in NYC was to increase connectedness to combat habitat fragmentation. This issue is applicable to civil engineering and construction as well because highways separate many creatures, but wildlife bridges serve as a way to let them travel safely.

Have a great Sunday, Jess 🙂

6 responses to “Oh, Rats!”

  1. How interesting, Jess. I had not considered wildlife bridges as a way to increase genetic diversity.

    Liked by 1 person

    1. Hello Tanja. Yes, traffic and urbanization limit the movement of animals when they travel to find food or mate. And since mating is one way to introduce new traits to a population, you can really see changes when populations aren’t mixing! Thanks for stopping by.

      Liked by 1 person

  2. We have a serious problem with rats. Some of them may look very nice, but they do not mind coming up onto the balcony and in the garden we can see some rats fighting with others or wanting them away from ‘their territory’. We can do with less rats. The one catch box with rat-poison does not seem enough to get the away from our garden and balcony. any solution? (Brown-gray rats, grey rats, grey rats with a black line on their back, a.o.)

    Liked by 1 person

    1. that’s unfortunate! i have had issue with house mice before but never rats.


  3. A really interesting post, thank you. I don’t find rats as troubling as many people; I appreciate their intelligence and resourcefulness,, but rats on islands are a serious problem. One example local to here in North Wales is Puffin Island- as its name implies it was once home to hundreds of breeding Puffins until a Lithuanian ship grounded and released rats onto it. The rats soon outnumbered the birds as they ate their eggs and chicks. Measures were taken to eliminate the rats with poison and it’s now free of them. A few pairs of Puffins had found sanctuary on the cliffs, but recovery is slow and there may be about 20 pairs there presently.

    Liked by 1 person

    1. wow I didn’t know about that! That could be damaging for the surviving puffins too because inbreeding can cause a lot of health issues. Thanks for the info 🙂

      Liked by 1 person

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