Genetic structure of populations of the Pampean grassland mouse, Akodon azarae, in an agroecosystem under intensive management

Agroecosystems in central Argentina are a good example of landscape modification by human activities. We used the Pampean grassland mouse (Akodon azarae) as a biological model to assess the effects of landscape fragmentation on the genetic structure of natural populations present in the region. The species is a habitat specialist that is numerically dominant in relatively stable environments, such as remnant areas of native vegetation, stream borders, roadsides and railway banks. We used seven microsatellite loci to analyze the genetic population structure and to explore if there is sex-biased dispersal during the reproductive season at a fine geographical scale. Rodents were captured seasonally in trap lines located on roadsides in an agroecosystem of central Argentina. Values of genetic differentiation among populations and temporal patterns of spatial autocorrelation revealed that the genetic populations occupy areas larger than the sampling area. Causal modeling analyses showed that unfavorable habitats (secondary roads and crop fields) were not barriers to dispersal of Akodon azarae. The high levels of gene flow and the short duration of the low population density phase, followed by a fast recovery, would contribute to the maintenance of highly polymorphic populations. As expected for A. azarae’s mating system, males were not genetically structured. However, females’ spatial genetic structure varied greatly over the year, which would be related to availability and quality of habitat, and to intrasex interactions. Our work contributes to the understanding of dispersal strategies in small mammals in anthropogenically fragmented habitats like intensively managed agroecosystems.