Analysis of phenotypic selection among locations in Impatiens pallida and Impatiens capensis

Abstract

Selection analysis of a set of quantitative traits was carried out in environmentally similar quadrats within natural populations of Impatiens capensis and Impatiens pallida to examine whether spatially heterogeneous directional selection is detectable when the range of environmental variation is restricted. While 25 of 96 different estimates of directional selection were significantly different from zero, there was only one instance in which directional selection of a quantitative trait was spatially heterogeneous among quadrats within species. The discovery of a low level of spatially heterogeneous selection supports previous results showing that spatially heterogeneous selection in these species is likely due to heterogeneity in abiotic features of the habitat, such as water and light availability, or to environmental factors correlated with these features. Measurements of the same set of characters examined in the selection analysis for 33 self-sib families of I. pallida indicate significant among-family variation in all instances. The evolutionary implications of these findings are discussed. Key words: natural selection, environmental heterogeneity, genetic variation, Impatiens pallida, Impatiens capensis.