Super mouse
Rice University researchers found mice are adept at evolving traits that make them resistant to a particular rodent poison not only through point mutation but also through horizontal gene transfer. Stefan Endepols/Bayer CropScie

Mouse are not longer just an annoying critter running about your house in the middle of the night. A few of them have proven to be resistant to poison.

Research from Rice University ecology and evolutionary biology professor Michael Kohn and his colleagues says thanks to a genetic mutation, the European house mouse is resistant to common poison. The gene is vkorc1, its present in mammals and manages Vitamin K. For the European house mouse, a mutated version of vkorc1 makes it resistant to warfarin, an anticoagulant used as a blood thinner in people as well as rodent poison.

The mice have evolved into having this rodent resistance from two processes. Point mutation is one. This is where genes adapt through spontaneous mutations during DNA replication. In this case, the desert dwelling Algerian mice acquired the mutation this way to counter a vitamin K-deficient diet.

The other process is horizontal gene transfer. In this case, the resistance was transferred directly from Algerian mice to European house mice. Kohn says it's rare for this to happen with mammals as usually it's a microbe process.

A key element of this study is that we've caught evolution in the act, said Kohn.

The whole thing occurred after a rodent pest-control specialist treating the basement of a German bakery said the mouse weren't dying when he sprayed the warfarin. When Kohn's team sequenced the mice for vkorc1 Kohn couldn't believe it.

I said, 'This cannot be a common house mouse. What type of animal did you send me here?' Kohn recalled. The gene sequence was identical to Mus spretus (the Algerian mice), which looks similar to house mice but does not normally occur in Germany. We could see that a big chunk of their DNA looked like Mus spretus. But genetically, these obscure bromadiolone-resistant mice looked like ordinary house mice. This is a freaky mouse.

This is where Kohn and company speculated the horizontal gene transfer. They thought it may have happened in the Spain or North Africa deserts, where the species overlap geographically.

In the very distant past, these mice wouldn't even meet, he said. With the spread of agriculture thousands of years ago in the Fertile Crescent, humans brought mice with them -- unwillingly. That brought these two types of mice into contact, and they started doing their thing, hybridizing here and there.

Kohn says this may be the first example where hybridization, two species combing to make a new one, was advantageous. He suggests these mammals may have adapted because of the rapid introduction of warfarin in the 1950s.

The result of this research actually brings concern to the human race according to Kohn.

One of the gravest concerns to conservation of biodiversity is the inadvertent spread of invasive species across the globe. In this study, this test came in the form of our desire to extirpate so-called pest species with poisons, which we use to get rid of microbes, bugs, weeds and even some mammals, he said.

The results of their research were published in a recent issue of Current Biology.

Follow Gabriel Perna on Twitter at @GabrielSPerna