EVOLUTION OF FLORAL TRAITS IN A HERMAPHRODITIC PLANT - FIELD-MEASUREMENTS OF HERITABILITLES AND GENETIC CORRELATIONS

Genetic variances, heritabilities, and genetic correlations of floral traits were measured in the monocarpic perennial Ipomopsis aggregata ( Polemoniaceae). A paternal half-sib design was employed to generate se eds in each of four years, and seeds were planted back in the field ne ar the parental site. The progeny were followed for up to eight years to estimate quantitative genetic parameters subject to natural levels of environmental variation over the entire life cycle. Narrow-sense he ritabilities of 0.2-0.8 were detected for the morphometric traits of c orolla length, corolla width, stigma position, and anther position. Th e proportion of time spent by the protandrous flowers in the pistillat e phase (''proportion pistillate'') also exhibited detectable heritabi lity of near 0.3. In contrast, heritability estimates for nectar rewar d traits were low and not significantly different from zero, due to hi gh environmental variance between and within flowering years. The esti mates of genetic parameters were combined with phenotypic selection gr adients to predict evolutionary responses to selection mediated by the hummingbird pollinators. One trait, corolla width, showed the potenti al for a rapid response to ongoing selection through male function, as it experienced both direct selection, by influencing pollen export, a nd relatively high heritability. Predicted responses were lower for pr oportion pistillate and corolla length, even though these traits also experienced direct selection. Stigma position was expected to respond positively to indirect selection of proportion pistillate but negative ly to selection of corolla length, with the net effect sensitive to va riation in the selection estimates. Anther position also was not direc tly selected but could respond to indirect selection of genetically co rrelated traits.