Genetic structure in urban and rural populations of Apodemus agrarius in Poland

The aims of this study were (i) to determine the genetic variability of the striped field mouse (Apodemus agrarius Pallas, 1771) population in the area of the Warsaw conurbation and the genetic differentiation among local populations of this species within the city, and (ii) to examine the influence of the degree of isolation on the appearance of such genetic structure. Comparison of the genetic structure of the urban population with that of populations inhabiting rural areas was intended to shed light on the depth of genetic changes in this species caused by life in an urban environment. Eight microsatellite loci were used for genotyping and these molecular analyses were successfully performed for 269 individuals. Genetic differentiation (FST) was much higher in the case of the urban population. STRUCTURE analysis indicated that this population was subdivided into several local populations, whereas for the rural locations, the highest likelihood was for a single genetic group (one genetically unstructured population). Moreover, in contrast to the rural population, we found no isolation by distance in the urban population. Despite clear subdivision of the urban population, the level of genetic variability was very similar in both analyzed groups. Our findings indicate the occurrence of an advanced process of differentiation of the urban population by microevolution, whereas populations from rural locations displayed very small and mainly insignificant genetic differentiation. Urban local populations, situated near the city borders or close to the natural ecological corridor (banks of the Vistula River), showed higher genetic variability and were less differentiated from populations inhabiting rural sites than from local populations in the city centre. These results provide support for the importance of ecological corridors in preserving the genetic variability of the urban striped field mouse population.