Dusty barns, shiny barns 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’ve been collecting mice from high-rises and rowhouses to learn more about the effects of city living on house mice. In short, we want to know whether there is a scientific basis for the tale of “The City Mouse and the Country Mouse”, in which cousins eat different foods depending on where they live.
Cities are hotter and large numbers of people live in high densities, which means more garbage and often more pollution. This could affect the evolution of species living in cities. Instead of open spaces and forests, artificial living spaces such as sidewalks, high-rise buildings and subways dominate in cities.
We are interested in many possible changes, but we are particularly interested in whether the many differences between urban and rural environments translate into genetic differences between urban mice and rural mice (for example, which versions of metabolism-related genes are more common).
We’re sequencing the genomes of mice to find the answers. With these data, we can answer a variety of questions, such as: Do urban mice have more or less genetic diversity than rural 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 these regions?
Why study house mice?
One reason we study house mice is because they are so common. European colonists brought house mice to America about 500 years ago. Rodents are now spread across many different climates and habitats in North and South America, most places where people live, including Philadelphia.
Despite their small size, house mice have made immeasurable contributions to genetics and medicine. They are mammals like humans, but house mice reproduce quickly and are relatively easy to breed and care for. In fact, one reason scientists early adopted mice as a model system is that people were already breeding “fancy mice” as pets. As a result, methods of preserving and breeding them were known.
Mice have many visible characteristics that geneticists need to examine. My team wants to learn more about the genes and traits that contribute to their ability to thrive in various environments. Our work with wild house mice also contributes to our work with laboratory mice and biomedical research. House mice found in attics and closets are identical to the species studied in laboratories, but are more genetically diverse than laboratory strains. Our project will produce complete genome sequences from many wild mice, and this data can help scientists studying traits and diseases.
Tips for catching mice
I previously worked on a large project examining how house mice adapted to different climates in America. For this project, I traveled to many farms in the eastern United States and had great success catching mice in barns.
Starting this project by focusing on cities was a new challenge. First, our team needed to find Philly residents who wanted us to trap 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 are tired of trying to rid their homes of mice. Some included videos of house mice escaping from traps they had set or stealing bait and running away. We share this disappointment and feel it deeply. In some cases, it took days to catch even a single mouse in an apartment.
One reason for this is that many houses in Philadelphia are old. This means they are often full of character and have holes that give mice great places to hide. It is difficult to lure mice out of their nests and into our traps. We’ve had the most success with peanut butter bait, which has a strong, attractive odor to mice. However, mice are omnivorous and eat a diverse diet that also includes insects. We’ve heard many stories from community members using baits like chocolate, cereal, cookies, and even bacon bits.
what’s next
We hope to begin sharing results within the next two years. We work in three cities, Philadelphia, New York City, and Richmond, Virginia, and have completed our first collections. Now we need to generate and analyze genetic data, so we are very busy in the laboratory.
In addition to DNA, we also extract another form of genetic material called RNA from different tissues. With DNA, we will examine how much genetic diversity there is in urban mouse populations and whether there are genetic differences between urban and rural mice. RNA will help us understand how differences in DNA translate into differences in metabolism, physiology, and other cellular processes.
We will also look for differences in features. For example, we will measure their skulls and skeletons. To learn about gut microbiomes and the collection of bacteria living in digestive tracts, we will sequence the DNA of microbes in the digestive tract and use stable isotope analysis to identify differences in their diets. Stable isotope analysis of diet uses the ratios of naturally occurring atoms of elements such as carbon and nitrogen to determine what type of food an organism eats.
Cities are full of wildlife. Learning how cities shape the evolution of mice could help us find better ways to manage mouse populations and other urban wildlife, as well as better understand evolution.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and authoritative analysis to help you understand our complex world. Written by: Megan Phifer-Rixey, Drexel University
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Megan Phifer-Rixey receives funding from the National Science Foundation (NSF CAREER 2332998 Environmental Biology Division).