He told her that he was having trouble getting rid of house mice in a German bakery, even after trying a powerful second-generation rodenticide called bromadiolone, or “super-warfarin”.
The officer sent over some of these resistant mice and when Song looked at their genes, she found a surprise.
This is a common theme – humans create a fatal chemical – a pesticide or an antibiotic – and our targets evolve resistance. Ying Song from Rice University, Houston, has found that some house mice picked up the gene for warfarin resistance from a different species. This vitamin activates a number of genes that create clots in blood, but it itself has to be activated by a protein called VKORC1.
Warfarin stops VKORC1 from doing its job, thereby suppressing vitamin K.
These rodents live in open, scrubby habitats and they feed mostly on seeds.
They don’t get a lot of food that’s rich in vitamin K, such as leafy green vegetables and Song thinks that their vkorc1 genes have adapted to help them cope with this vitamin deficiency – indeed, it’s one of the fastest-evolving genes in its entire genome.
At a time when humans were using warfarin and related poisons, these hybrid mice had suddenly gained a valuable defence, one powerful enough to compensate for their other disadvantages.
They survived and mated with other house mice, spreading the resistance gene to their own pups.
In this way, the mice are rather reminiscent of bacteria.
Our attempts to kill them merely unveiled a strength that had been hiding for centuries.
Reference: Song, Endepols, Klemann, Richter, Matushcka, Shih, Nachman & Kohn. Adaptive Introgression of Anticoagulant Rodent Poison Resistance by Hybridization between Old World Mice.
Since 1948, people have been poisoning unwanted rats and mice with warfarin, a chemical that causes lethal internal bleeding.