Genetic structure of the cyclic fossorial water vole (Arvicola terrestris): landscape and demographic influences.

Genetic structure can be strongly affected by landscape features and variation through time and space of demographic parameters such as population size and migration rate. The fossorial water vole (Arvicola terrestris) is a cyclic species characterized by large demographic fluctuations over short periods of time. The outbreaks do not occur everywhere at the same time but spread as a wave at a regional scale. This leads to a pattern of large areas (i.e. some hundreds of km2), each with different vole abundances, at any given time. Here, we describe the abundance and genetic structures in populations of the fossorial water vole. We use the data to try to understand how landscape and demographic features act to shape the genetic structure. The spatial variability of vole abundance was assessed from surface indices, collected in spring 2002 (April) in eastern central France. Genetic variability was analysed using eight microsatellite loci at 23 localities sampled between October 2001 and April 2002. We found some congruence between abundance and genetic structures. At a regional scale, the genetic disruptions were associated with both sharp relief and transition between an area of low abundance and another of high abundance. At a local scale, we observed a variation of the isolation-by-distance pattern according to the abundance level of vole populations. From these results we suggest that the dispersal pattern in cyclic rodent populations varies throughout the demographic cycle.