Landscape discontinuities influence the population structure of Acer opalus ssp. obtusatum Waldst. & Kit. ex Willdenow

The major goal of landscape genetics is to understand how landscape structure genetic variation in natural populations. We investigated molecular diversity in Acer opalus subsp. obtusatum sampled from 95 sites using 14 nuclear microsatellite loci. The average number of alleles per nuclear microsatellite locus differed among sampling sites; the number was high (4.9 alleles) in populations from the Basilicata and Molise regions, where heterozygosity was also high (0.679, Molise; 0.669, Basilicata). Differentiation between sites was often low (mean FST ¼ 0.220), indicating few genetic differences between most sites. There was a clear excess of homozygotes (mean Ho ¼ 0.450, mean He ¼ 0.513) and a relatively high FIS (mean ¼ 0.451), suggesting a consistent level of inbreeding in many A. opalus subsp. obtusatum populations. There was a significant pattern of isolation by distance across the study area (Mantel test; R 2 ¼ 0.0662, P , 0.001). Two assignment methods (Structure and Geneland) produced some similarities in their definitions of population structure, especially for populations from the Campania and Tuscany regions. These two important genetic discontinuities were not associated with any physical barriers