Individual spatial aggregation correlates with between-population variation in fine-scale genetic structure of Silene ciliata (Caryophyllaceae)

Abstract

Fine-scale genetic structure (FSGS) can vary among populations within species depending on multiple demographic and environmental factors. Theoretical models predict that FSGS should decrease in high-density populations and increase in populations where individuals are spatially aggregated. However, few empirical studies have compared FSGS between populations with different degrees of individual spatial aggregation and microhabitat heterogeneity. In this work, we studied the relationship between spatial and genetic structure in five populations of alpine specialist Silene ciliata Poiret (Caryophyllaceae). We mapped all individuals in each population and genotyped 96 of them using 10 microsatellite markers. We found significant FSGS consistent with an isolation-by-distance process in three of the five populations. The intensity of FSGS was positively associated with individual spatial aggregation. However, no association was found between FSGS and global population density or microhabitat heterogeneity. Overall, our results support theoretical studies indicating that stronger spatial aggregation tends to increase the magnitude of FSGS. They also highlight the relevance of characterizing local plant distribution and microhabitat to better understand the mechanisms that generate intraspecific variation in FSGS across landscapes.

Figure 1

Spatial distribution of adult plants (a), spatial demographic structure (b) and spatial genetic structure (c) in Silene ciliata study plots. (a) Spatial distribution of adult plants (small circles), rocks (grey) and shrubs (dark grey) in each study plot of S. ciliata. (b) Spatial demographic structure: b_LO(r) denotes the slope of the regression of the O ring statistic, O_(r) on the logarithm of the spatial distance, ln(r); the thin solid line indicates average intensity of the point pattern (that is, plant density) and dashed lines indicate 95% confidence envelopes under the null hypothesis of random spatial structure. Note that y axes show different scales for clarity. (c) Spatial genetic structure: b_Ld denotes the slope of the regression of kinship coefficient values (F_ij) on the logarithm of the spatial distance, ln (d_ij); dashed lines represent 95% confidence envelopes constructed under the null hypothesis (no genetic autocorrelation exists). **P<0.01, ***P<0.001.

Figure 2

Association between spatial autocorrelation measures of fine-scale genetic structure (b_Ld) and individual spatial aggregation (b_LO(r)); ‘r' indicates Pearson's product-moment correlation.

Figure 3

Association between the fine-scale spatial genetic structure (Sp) and (a) adult density (D) and (b) microhabitat heterogeneity (SI); ‘r' indicates Pearson's product-moment correlation.