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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

Original publication




Journal article


Functional Ecology

Publication Date





190 - 194