Genetic consequences of habitat fragmentation in an agricultural landscape on the common Primula veris, and comparison with its rare congener, P-vulgaris

In Flanders (northern Belgium), the common (but locally rare) P veris and its rare relative Primula vulgaris, two self-incompatible perennials, mainly occur in fragmented habitats of the intensively used agricultural landscape. We investigated genetic variation and structure for respectively 30 and 27 allozyme loci in 24 and 41 populations of P. veris and P. vulgaris, in relation to species (local) abundance and to population size and plant density, and compared populations of linear landscape elements (verges) with non verge populations. The rare P. vulgaris was,genetically depauperate compared to the commoner P. veris. Both species showed a geographical structure of genetic variation and isolation by distance. The scattered populations of P. veris from the Westhoek region (polder habitats) were of smaller size, genetically depauperate and showed higher interpopulation divergence compared to the Voeren region, where populations are densely distributed and habitats less fragmented. Verge and non verge populations showed similar populations sizes and levels of genetic variation. For both species, small populations showed a loss of genetic variation, but still maintained high levels of observed heterozygosity. Within-population plant density negatively affected allelic richness in P. veris. Ours results indicate that common species can also be negatively affected by habitat fragmentation (perhaps even more so than rare species) and that verge populations can have a high potential conservation value. Both verge and non-verge populations should be included in conservation efforts.