Résumé
Dispersal may be strongly influenced by landscape structure and habitat characteristics that could either enhance or restrict movements of organisms. Therefore, spatial heterogeneity in landscape structure could influence gene flow and the spatial structure of populations. In the past decades, agricultural intensification has led to the reduction of grassland surfaces, their fragmentation and intensification. Since these changes are not homogeneously distributed in space, they might result in spatial heterogeneity in population’s genetic structure. Understanding the effect of landscape structure and habitat characteristics is thus critical for both studies in biodiversity conservation andpest’s management. In this study, we used eight microsatellite loci to assess spatial genetic structure and landscape genetics relationships of Pezotettix giornae, a small-sized grasshopper specialized on grassland and herbaceous habitats. Because it has wings unfit for flight, its ability to disperse long distances is supposed to be weak. We collected 1097 individuals from 231 grasslands in a 100 x 100 km agricultural area of Western France. While the northern part of the study area consists of preserved hedged farmland, the southern part has been profoundly converted for intensive crop production after WWII, with generally less intensified hedged farmland areas remaining alongside streams and rivers. Over the entire study area, we did not detect genetic clusters in relation with landscape features. Spatial genetic autocorrelation analysis suggested small-scale dispersal, and the grasshopper population was characterized by a heterogeneous pattern of isolation by distance. We used individual-based landscape genetics approaches to investigate how landscape structure and habitats characteristics affect P. giornae genetic diversity and gene flow. Altogether, results suggested that, in the most intensive agricultural areas, P. giornae dispersal is enhanced by disturbance due to increasing habitat turnover. As a long-term consequence, one could expect the selection of increasing dispersal capacities. This hypothesis is consistent with differences measured on dispersal-related traits among P. giornae individuals from areas with contrasted level of disturbance.