Comparative landscape genetics of gypsum specialists with naturally-patchy distributions reveal their resilience to anthropogenic fragmentation

Gypsum endemics occur in naturally-fragmented habitats, which may lead to genetic erosion and higher vulnerability to the genetic effects of anthropogenic fragmentation. Conversely, evolution in a fragmented landscape could increase their resilience to the effects of further fragmentation, but no evidence is available in either direction. In this study, we capitalize on previous results showing high genetic variation and a negative, yet small, effect of fragmentation on genetic variation on the gypsophile Lepidium subulatum, and jointly assess two other co-occurring dominant gypsophiles: Helianthemum squamatum and Centaurea hyssopifolia. We sampled individuals of the species in 20 populations varying in their fragment size and connectivity (≈400 plants/species; 1138 individuals total), and assessed genetic variation and population structure using species-specific microsatellite markers. Genetic variation was high in populations of the three study species, as shown by the high expected heterozygosity (0.454-0.735) and allelic richness (2.875-8.125). Population differentiation was in general low, but H. squamatum showed a stronger spatial structure than the other species. No effects of fragment size or connectivity were found for H. squamatum or C. hyssopifolia, i.e. differences among populations in genetic variation were not related to the size or connectivity of the sampled habitat remnants. These results contrast with the expectation that habitat specialists may be genetically impoverished. Furthermore, the correlation of key genetic diversity indices among species suggests that some fragments harbor more genetically-diverse populations than others, which provides insights for their conservation. We propose that these species may offset the genetic effects of human-mediated further habitat loss and increased isolation.