Population structure and warfarin resistance in the brown rat, (Rattus norvegicus) in the English countryside

The brown rat, Rattus norvegicus is a relatively recent addition to the English fauna. However it is currently one of the most important vertebrate pest species. Anticoagulant rodenticides are the major control method used for the last 50 years. Widespread use of the rodenticide has led to evolution of resistance leading to problems controlling brown rat populations. One thus far ignored aspect of resistance biology is the population structure of the brown rat. In this research mitochondrial DNA and microsatellite DNA were used to elucidate the population structure of the brown rat at different scales in the English countryside. I also report on the type and the distribution of different warfarin resistant mutations in the English rural population.;Mitochondrial DNA data suggests a structured population at county level and the English brown rat population as a whole appears not to be at equilibrium. The relative lack of diversity in the mitochondrial DNA sequences examined can be explained by a founder effect and a subsequent spatial expansion. However, the microsatellite data shows much more mixing of populations at county level, even more clearly at the farm level. I discuss two possible explanations for this discrepancy; small effective population size of mitochondrial genomes and the greater movement of males compared to female rats.;Through mutation analysis we found 3 types of mutations in the exon 3 region of the VKORC1 gene among our brown rat populations. One mutation type is almost ubiquitous being found in almost all counties. We also found a geographical pattern to the different mutation distribution. As these mutations are also found in other parts of Europe, we suggest that they have entered England through different ports from different parts of the Continent which would explain the geographical structure of the mutations.