Spatial patterns of polygenic variation in Impatiens capensis, a species with an environmentally controlled mixed mating system

Abstract

Impatiens capensis displays a mixed mating system in which individual out-crossing rate is expected to increase with light and resource availability. We investigated the amount and spatial distribution of polygenic variation for 15 morphological traits within and among six natural populations of I. capensis growing in three distinct light habitats (shaded, mixed, full sun). We grew individuals from each population in uniform greenhouse conditions and detected significant genetic variation among families within populations for all the quantitative traits examined. However, only the features related to the vegetative characteristics of seedlings and sexually mature plants show also differentiation at the population level. Surprisingly, even though light availability is likely to be the most important factor affecting the mating system of I. capensis, we find that: (1) trait means of individuals from similar light environments are not more similar than those from different light environments; (2) partitioning of polygenic variance within and among families differs both among populations from the same light habitat and among characters within each population. If natural selection is maintaining such variation, it must operate primarily through heterogeneous selection pressure within, rather than between, populations.