fat rats that love their poison

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rats living in an undisclosed part of southern England seem to have grown resistant to rat poisons without paying the usual biological penalty. Monitoring has been stepped up across the country to find out if this characteristic is widespread. reistance to the poison warfarin has been known since the 1960's but there was always thought to be some price to pay. Warfarin-resistant rats are usually smaller and lighter than susceptible rats from the same populations. This meant that while the resistant rats have the advantage in the survival stakes when the warfarin is being used, when there is no poison around they lose out because social dominance-and success in feeding and breeding-depends largely on size and weight. however, researchers from the universities of Reading in OXford have found some rats that seem to suffer none of the disadvantages that usually accompany the gene for resistance.