'Super' mouse evolves resistance to most poisons

Scientists say that some European house mice have developed resistance to the strongest poisons, BBC reports.

German and Spanish 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 between different species is highly unusual and normally found in plants and bacteria.

They are concerned that this rare form of rapid evolution could herald the spread of new generations of rodents resistant to almost any form of chemical pest control.

Warfarin is a drug widely used in medicine as an anticoagulant to prevent the build up of harmful blood clots. It works through inhibiting a protein called VKORC1. This protein turns on our ability to produce vitamin K which is essential for clotting.

Too much warfarin can cause fatal bleeding, and it was this quality that lead to its introduction as a pesticide against rats in mice in the 1950s.

But rats and mice have been slowly evolving traits to survive warfarin and pockets of resistant rodents have been found in many different parts of the world.

Now scientists say that German and Spanish mice have found a rapid method of overcoming the threat by cross breeding with Algerian mice that are, according to the researchers, an entirely different species.

Professor Michael Kohn from Rice University in Houston, Texas, led the team of researchers who carried out the work.

"Our study is so special because it involves hybridization between two species of mouse that are 1.5 to three million years removed from each other.

"Most of the offspring... do not reproduce, they are sterile - but there is a small window, which remains open for genes to be moved from one species to the other, and that's through a few fertile females, so there is a chance to leak genes from one species to another."

Thanks to these few fertile females, the vast majority of mice in Spain and a growing number in Germany have acquired resistance over a very short period of time, although scientists aren't exactly sure when the first genetic exchanges took place.

And while they may not look any different to regular household mice, in their genetic code they now have the ability to survive the strongest chemicals in the pest control armory.

"There are a lot of genetic barriers between these species of mice, to see them hybridize and transfer genetic material is quite spectacular to be frank," said Professor Kohn.

Professor Kohn believes that his research is an example of what scientists call horizontal gene transfer, a process normally seen in bacteria and plants but rarely in animals.

"There have been some accusations that we had oversimplified things by saying this is horizontal gene transfer - I believe that it is, but it is more special than that, because it has to overcome this hurdle of hybrid sterility in the first generation of offspring at the very least."

Other scientists aren't so sure. Dr Julie Dunning Hotopp is from the Institute for Genome Science at the University of Maryland, US. She says the house mouse story does not meet her definition.

"It's interesting work - but I wouldn't call it horizontal gene transfer, which I would say was gene exchange in the absence of sex.

"In many respects I don't think it's surprising, anytime you have a strong pressure like a pesticide, you will have the opportunity to have these changes.

"As humans we are applying more pressure, but we can observe the changes more easily as well thanks to improved genomic sequencing. We will find more examples like this because we can look for more."

For original see: http://www.bbc.co.uk/news/science-environment-14462733