Fine-scale genetic structure in populations of the spring ephemeral herb Megaleranthis saniculifolia (Ranunculaceae)

Fine-scale genetic structure (FSGS) in plants occurs primarily through restricted seed dispersal. Analyses of FSGS have been used retrospectively to infer seed dispersal and other ecological processes. The spring ephemeral Megaleranthis saniculifolia, endemic to Korea, is insect-pollinated and has no special seed dispersal mechanism, and its seedling recruitment is quite low. Given these ecological and life-history traits, we expect that there would be significant FSGS in juveniles, which would persist into adult stage. Since M. saniculifolia is self-compatible and many adults produce 2-3 inflorescences, we expect considerable inbreeding. To test these predictions, we used allozyme-based Sp statistics to compare two undisturbed populations on Mt. Deogyu (DEO) and Mt. Taebaek (TAE), as well as between juveniles (J) and adults (A) stages. We also measured genetic diversity and inbreeding in each population. The two populations exhibited significant FSGS in both life stages. Although the strength of FSGS was reduced with increasing stage (J, Sp = 0.0313; A, Sp = 0.0178 in DEO and J, Sp = 0.0502; A, Sp = 0.0286 in TAE), differences in FSGS between stages and between populations were not significant. Within-population genetic diversity (mean %P = 27.0, A = 1.27, He = 0.116) was relatively low and comparable to reference values for both endemic and narrowly-distributed plant species. Genetic differentiation between sites, however, was high (FST = 0.465), and the two populations exhibited a significant deficit of heterozygotes (mean FIS = 0.289), primarily due to selfing and biparental inbreeding (effective selfing rate was ∼0.40). Our results revealed that the magnitude and spatial scale of FSGS in M. saniculifolia is strong and does not differ significantly with life-history stage. The strong FSGS, low within-population genetic variation, high between-population genetic differentiation, and high inbreeding are consistent with the species' limited seed dispersal and a mixed mating system.