Animal Biology 59 (2009) 169–187 brill.nl/ab © Koninklijke Brill NV, Leiden, 2009 DOI 10.1163/157075609X437691 he spatial genetic structure of bank vole ( Myodes glareolus) and yellow-necked mouse ( Apodemus flavicollis ) populations: he effect of distance and habitat barriers Michal Kozakiewicz 1, *, Tomasz Gortat 1 , Hanna Panagiotopoulou 1 , Alicja Gryczyńska– Siemiątkowska 1 , Robert Rutkowski 2 , Anna Kozakiewicz 1 , Katarzyna Abramowicz 1 1 Department of Ecology, University of Warsaw, Banacha 2, 02-097 Warsaw, Poland 2 Museum and Institute of Zoology Polish Academy of Sciences, Wilcza 64, 00-679 Warsaw, Poland Abstract Habitat barriers are considered to be an important factor causing the local reduction of genetic diversity by dividing a population into smaller sections and preventing gene flow between them. However, the “barrier effect” might be different in the case of different species. he effect of geographic distance and water barriers on the genetic structure of populations of two common rodent species – the yellow- necked mouse ( Apodemus flavicollis) and the bank vole ( Myodes glareolus) living in the area of a lake (on its islands and on two opposite shores) was investigated with the use of microsatellite fragment analy- sis. he two studied species are characterised by similar habitat requirements, but differ with regard to the socio-spatial structure of the population, individual mobility, capability to cross environmental barri- ers, and other factors. Trapping was performed for two years in spring and autumn in north-eastern Poland (21 o E, 53 o N). A total of 160 yellow-necked mouse individuals (7 microsatellite loci) and 346 bank vole individuals (9 microsatellite loci) were analysed. he results of the differentiation analyses (F ST and R ST ) have shown that both the barrier which is formed by a ca. 300 m wide belt of water (between the island and the mainland) and the actual distance of approximately 10 km in continuous populations are sufficient to create genetic differentiation within both species. he differences between local popula- tions living on opposite lake shores are the smallest; differences between any one of them and the island populations are more distinct. All of the genetic diversity indices (the mean number of alleles, mean allelic richness, as well as the observed and expected heterozygosity) of the local populations from the lakeshores were significantly higher than of the small island populations of these two species separated by the water barrier. he more profound “isolation effect” in the case of the island populations of the bank vole, in comparison to the yellow-necked mouse populations, seems to result not only from the lower mobility of the bank vole species, but may also be attributed to other differences in the animals’ behaviour. © Koninklijke Brill NV, Leiden, 2009 Keywords Apodemus flavicollis; Myodes glareolus; microsatellite loci; gene flow; habitat isolation; genetic structure * ) Corresponding author; e-mail: kozak@biol.uw.edu.pl