Why Are Spanish Mice Resistant To A Common Poison?

Aug 10, 2011

Here's a piece of biology news that escaped us, last month, but was brought to our attention by a story in the BBC today: Biologist have found the reason house mice in Spain and Germany have grown immune to warfarin, a commonly used poison.

The idea of a poison-resistant mouse is a bit unsettling, but how it came to be is fascinating tale of cross-species sex. The BBC reports:

[The] mice have rapidly evolved the trait by breeding with an Algerian species from which they have been separate for over a million years.

The researchers say this type of gene transfer is highly unusual and normally found in plants and bacteria.

The Current Biology report says this process could yield mice resistant to almost any form of pest control.

So in simple terms, what they are talking about here is that these mice are kind of the equivalent of a mule, which comes about when a male donkey is bred with a female horse. Now what makes this special is that hybridization has been seen as a bad evolutionary move because it's a dead end. Most hybrids — mules for example — are infertile.

So what happened here and how did most mice in Spain become immune to the poison? Warfarin, explains Science, works by inhibiting "a protein called VKOR, which is important for recycling vitamin K, a vital component in blood clotting." Algerian mice are naturally resistant to warfarin.

Science explains:

"We are looking at two species that are 1.5 million to 3 million years removed," [Biologist Michael Kohn of Rice University in Houston] says. Even though the two rodents overlap in parts of Africa and Europe, they don't usually interbreed—and if they do, all male offspring and some female offspring are sterile. Yet, "that narrow window of a few fertile females must have been enough to leak DNA," Kohn says. The researchers show that the house mice successively lost most of the foreign DNA except for a chunk of DNA that includes the resistance.

Of course this super mouse is all our fault, as Discover Magazine explains:

Humans were probably responsible for these lucky liaisons. The two species used to live in completely different parts of the world. They would never have met, had humans not brought house mice with them as they expanded into Western Europe. Once the two species showed up in the same place, they started mating. Later, humans were again responsible for giving the hybrids an edge over their pure-bred house mouse relatives. Our attempts to kill them merely unveiled a strength that had been hiding for centuries.

Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.