A new aspect of warfarin resistance in wild rats: benefits in the absence of poison

Resistance to the anticoagulant poison warfarin in brown rat Rattus norvegicus is thought to incur a cost: resistant rats are prone to vitamin K deficiency, show reduced growth rates and reduced viability resulting in a lower fitness for resistant rats in a warfarin-free environment. The authors investigated the costs of warfarin resistance in terms of body weight, an indicator of resistance costs and a component of fitness, in two populations of wild rats containing resistant individuals from southern England. In a warfarin-free environment, resistance remained high and contrary to predictions, most resistant individuals were signficantly heavier than susceptible animals in both populations. This is the first report of a possible selective advantage of warfarin resistance in the absence of poison. -from Authors