by Dusty barns, dingy stables and damp basements. These are all places where you might find a house mouse – or a member of my research team.
I’m an evolutionary biologist, and my lab at Drexel University studies wild house mice. With the help of Philly residents, we’re collecting mice from high-rises and row houses to learn more about the effects of city living on house mice. In short, we want to know if there is any scientific basis to the story of “The Town Mouse and the Country Mouse” where the cousins eat differently based on where they live.
Cities are hotter and many people live in high densities, which means more trash and usually more pollution. This can affect how species living in cities evolve. Artificial habitats such as footpaths, high-rises and subways rather than open parks and forests also dominate cities.
We are interested in many possible changes, but especially in whether the many differences between urban and rural environments translate into genetic differences between city and country mice, such as the versions of genes associated with more common metabolism.
To find the answers, we sequence the genomes of mice. With that data, we can answer various questions, for example: Do city mice have more or less genetic diversity than country mice? Are there regions of DNA, the molecule that encodes genetic information, that are consistently different between urban and rural mice? If so, what are the functions of the genes in those regions?
Why study house mice?
One reason we study house mice is because they are so widespread. European colonists brought house mice to America about 500 years ago. The rodents have spread into many different climates and habitats throughout North and South America in most inhabited places, including Philadelphia.
Although small in size, house mice make important contributions to genetics and medicine. They are mammals like humans, but house mice reproduce quickly and are relatively easy to breed and maintain. In fact, part of the reason scientists early adopted mice as a model system was that people were already breeding “fake mice” as pets. As a result, he knew methods to keep and breed them.
Mice have many observable traits that geneticists can study. My team wants to know more about the genes and traits that have contributed to their ability to thrive in different environments. The work we do with wild house mice feeds back into work with laboratory mice and biomedical research. The house mice found in attics and cabinets are the same species studied in laboratories, but they are more genetically diverse than laboratory strains. Our project will generate whole genome sequences from many wild mice, and that data can help scientists studying traits and diseases.
Tips for catching mice
I previously worked on a large project studying how house mice adapted to different climates in America. For that project, I went to many, many farms across the eastern United States and was very successful at catching mice in barns.
Starting this project with a focus on cities was a new challenge. First, our team had to find Philly residents who wanted us to catch their mice. We spent a lot of time spreading the word on social media, talking to friends and posting flyers.
We talked to many Philadelphians who were frustrated trying to get rid of mice from their homes. Some had videos of house mice avoiding the traps they set or stealing the bait and running away. We share this frustration and feel it keenly. In some cases, it took us many days to catch one mouse in an apartment.
Part of the reason is that many Philadelphia homes are old. This means they are often full of characters – and holes that provide great hiding places for mice. It is difficult to lure the mice out of their nests and into our traps. We have had the most success with peanut butter bait, which has a strong smell and is very attractive to mice. But mice are omnivores, eating a varied diet that includes insects. We have heard many stories from members of the public who have used bait such as chocolate, cereal, cookies and even bacon bits.
What lies ahead
We hope to start sharing results over the next two years. We are working in three cities – Philadelphia, New York City and Richmond, Virginia – and have completed our first collections. Now we have to generate and analyze genetic data, so we are very busy in the lab.
We are extracting DNA, as well as another form of genetic material called RNA, from various tissues. With the DNA we will study how much genetic variation there is within the city’s mouse populations, and whether there are genetic differences between urban and rural mice. The RNA will help us understand how differences in DNA translate to differences in metabolism, physiology and other cellular processes.
We will also look to see if there are differences between the characteristics. For example, we will measure their skulls and skeletons. We will sequence the DNA of the microbes in their digestive system to learn about their gut microbes, collect the bacteria that live in their digestive system, and use stable isotope analysis to identify any differences in their diets. Stable isotope analysis of diet uses the ratios of natural atoms of elements such as carbon and nitrogen to determine what types of food an organism ate.
Cities are full of wildlife. Learning how cities shape the evolution of mice may help us find better ways to manage populations of mice and other urban wildlife and better understand the evolution of cities.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. It was written by Megan Phifer-Rixey Drexel University
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Megan Phifer-Rixey receives funding from the National Science Foundation (NSF CAREER 2332998 Division of Environmental Biology).
