A. RIEUX, T. LENORMAND, J. CARLIER, L. DE LAPEYRE DE BELLAIRE and V. RAVIGNE
On the use of temporal variation in neutral genetic clines to estimate gene flow: a case study in a fungal plant pathogen
Neutral genetic clines theory provides a powerful conceptual framework to estimate the strength of dispersal in natural populations, especially in the case of populations deviating from genetic equilibrium. In the present study, we introduce a method based on the analysis of the rate of change in the shape of clines observed at unlinked neutral markers and further apply this method in the case of a plant pathogen fungus along a secondary contact geographic area in which two genetically differentiated populations have been previously detected. We observe genetic clines of allelic frequencies at 8 out of the 15 microsatellites markers studied and further analyse the temporal evolution of these multilocus genetic clines over 2 years (approx. 15 generations). We show that all cline centres are coincident and stable in time. In addition, over the studied period, these clines gradually vanish at a common pace. These findings are consistent with the hypothesis that clines evolve under the effect of migration only and that this migration is isotropic along the considered area. Confronting a theoretical model of the temporal dynamics of neutral genetic clines under migration, we estimate the intensity of gene flow in this area. Under diffusion approximation and assuming constant migration through time, we find that σ, the so-called root square in axial parent-offspring distance is equal to 1175 metres/generation. Finally theoretical simulations show that the method of migration estimation is robust to deviations to diffusion approximation and the time since secondary contact. Our results illustrate that combining landscape genetics approaches to detect sharp breaks in allelic frequencies distribution over space with analyses of genetic clines temporal variation offers a convenient way to gain solid information on gene movements.