Spatial position and microsatellite genotyping of S. ciliata plants

Abstract

The patterns and intensity of fine-scale spatial genetic structure (FSGS) can vary among populations within species depending on the interplay between different demographic and environmental factors. Theoretical models predict that FSGS will increase especially with local density variation due to static habitat heterogeneities, but few empirical studies have examined the differences in FSGS among populations with different degrees of spatial heterogeneity. In this study we used spatial autocorrelation methods to assess spatial demographic and genetic structures of five demographically stable but spatially heterogeneous populations of high-mountain specialist Silene ciliata Poiret (Caryophyllaceae). In each population we recorded the geographical location of every individual and genotyped 96 of them using 8 microsatellite markers. We found significant FSGS in three out of the five populations and a significant positive association between spatial demographic and genetic structures, thereby supporting the importance of fine-scale aggregation of plants on intraespecific FSGS variation. Contrary to previous findings in other plant species, the population with highest plant density was the one with strongest FSGS, probably due to reduced long-term gene dispersal rates in fragmented habitats and lower pollinator mobility in response to high densities and spatial aggregation of plants. Overall our results support the importance of fine-scale aggregation of plants on intraspecific FSGS variation, and stress the importance of combining FSGS analyses with explicit characterization of local spatial distribution of individuals and habitat to better understand the mechanisms generating intraspecific variation in FSGS across landscapes.