Mouse Hunt

Rodent-catching students are helping Tanya Chubb solve genetic mysteries by Caitlin Sykes.

When a mouse gets caught in your house you probably think it's kind of gross - then throw it out as quickly as you can. You probably don't stop to think about its ancestors and where they came from; if they sailed long distances to our shores with rowdy sealers and whalers more than 100 years ago, for example, or were the quiet stowaway companions of our hardy colonial settlers. But Tanya Chubb does.

Tanya is studying New Zealand house mice, and where they come from, for her Master's research project at Waikato University. She's looking at the genetic sequences of house mice found here and comparing them to those of other mice found around the world. In doing so, she not only finds out where our mice originally came from - sometimes down to a particular country, or even city - but how their populations have evolved and changed over time. Because, for little guys, mice sure do get around.

We have three different kinds of mice in New Zealand, Tanya explains: Mus musculus musculus, which come from Eastern Europe, Mus musculus castaneus, which come from South-east Asia and Mus musculus domesticus, which come from Western Europe. "Mice are commensal beings, which means they live with humans. So where we are, they are," says Tanya. "And they travel with us, so they will travel in trucks and trains and all places."

Tanya's been researching mice from three different areas in New Zealand: the Chatham Islands, the lower North Island, and Hamilton (where's she's based). She's collected the mice herself from the Chatham Islands and Hamilton, but has been relying on a dedicated team of students at five primary and two high schools to trap the rodents in the lower North Island. The students, living mostly in rural areas, catch the mice around their homes. They then bring their (dead) captures to school, where their teachers store them in the freezer until Tanya makes a pickup. On her first pickup trip, Tanya collected 45 mice from the students. Says Tanya: "One young girl in Ekatahuna caught 17 in her calving shed. I was impressed!"

Once Tanya has taken the mice back to her lab that's where technology comes in. She'll take a small clipping from a mouse's ear and extract out the DNA. She then uses something called polymerase chain reaction (PCR), which works a bit like a genetic photocopier, to make copies of the genetic material. Then she sends that material off to be sequenced. This process involves using computer programs to work out the gene sequence, using the four codons - ATGC. Once Tanya has the sequences back, she edits them using a computer program called Sequencher, then enters the edited sequences into another program, called PAUP* (pronounced 'pop star'). This works out what's called a phylogenetic, or evolutionary tree, which shows Tanya how the different mice are related to each other and where hybrids - or crosses - have come from.

The last step involves entering the phylogenetic trees into GenBank, a massive online gene database, so she can see which other mice around the world are most closely related to the ones she's studying.

But the question you might be asking is, why?

Well, explains Tanya, the information she gathers about evolutionary changes in mice can be applied to other species. Say you have an endangered species, for example. If you can find an individual from one population of that species that's not so closely related and introduce it to another population, you might be able to increase genetic variability. And that variability is good because it means the population will be healthier and more likely to survive. So those students are working for a good cause. And Tanya's on the lookout for more mouse catchers, particularly in her home town of Hamilton where she's had a particularly interesting find. So if you're interested, give us a squeak!