The effect of segregation of flowering time on fine-scale spatial genetic structure in an alpine-snowbed herb Primula cuneifolia.

The flowering phenology of alpine-snowbed plants varies widely depending on the time of snowmelt. This variation may cause spatial and temporal heterogeneity in pollen dispersal, which in turn may influence genetic structure. We used spatial autocorrelation analyses to evaluate relative effect of segregation in flowering time and physical distance on fine-scale spatial genetic structure (SGS) of a snowbed herb Primula cuneifolia sampled in 10-m grids within a continuous snow patch (110 x 250 m) using nine allozyme loci. Although the individual flower lasts for </=10 days, flowering season varied over 50 days from late June to the middle of August within the plot. The effect of flowering phenology on SGS was assessed using spatial autocorrelation analyses based on the pairwise kinship coefficients for all sampled plants (control pairs), plants with flowering overlap (co-flowering pairs) and plants with separate flowering season (non-co-flowering pairs). The degree of SGS increased as the extent of flowering segregation increased: co-flowering pairs < control pairs < non-co-flowering pairs, indicating substantial effect of restriction in gene flow due to phenological heterogeneity. Flowering segregation caused by snowmelt timing is a critical factor for reinforcing the fine-scale SGS in this species.