Spatial genetic heterogeneity in a population of the montane perennial plant delphinium nelsonii

Abstract

The montane perennial herb Delphinium nelsonii experiences restricted pollen and seed movement and spatial environmental heterogeneity, features likely to promote genetic differentiation within populations. To explore this possibility, allele frequencies at 5 polymorphic loci were characterised along transects through a meadow. F-statistics indicated substantial heterozygote excess within transect samples (overall FIS = –0·096). Possible contributors are sex-biased gene flow, and events occurring between pollination and ovule fertilisation that favor pollen from an “optimal outcrossing distance” of 3–10 m. Higher mating success over this optimal distance should cause longer realised gene dispersal than expected from pollen and seed movement, which are 1 m on average. It also may bring about a “leapfrog” dispersal pattern instead of a monotonic decline with distance from a source plant. F-statistics also indicated moderate genetic differentiation among samples (overall FST = 0·069). However, this did not correspond to organised spatial pattern. Spatial autocorrelations showed that alleles were randomly distributed along transects. Although mean genetic distance increased with physical distance, the pattern was not statistically significant. Apparent random spatial heterogeneity is expected if gene flow is extensive enough to prevent a rapid decline in genetic correlation with distance; it also might be promoted by a leapfrog pattern of gene flow. © 1987 The Genetical Society of Great Britain.