ENVIRONMENT-DEPENDENCE OF QUANTITATIVE GENETIC-PARAMETERS IN IMPATIENS-PALLIDA

Population response to selection depends on the presence of additive g enetic variance for traits under selection. When a population enters a n alien environment, environment-induced changes in the expression of genetic variance may occur. These could have large effects on the resp onse to selection. To investigate the environment-dependence of geneti c variance, we conducted a reciprocal transplant experiment between tw o ecotypically differentiated populations of Impatiens pallida using t he progeny of a standard mating design. The floodplain site was charac terized by high water availability, moderate temperatures, and continu ous dense stands of Impatiens. The hillside site was drier, with large r temperature extremes and supported only scattered patches of Impatie ns with significantly lower seed production and earlier mortality. Est imates of heritability were low for each of the 13 trails measured in each population and site (range from 0-28%). Additive genetic variance for life-history traits tended to be larger than for morphological tr aits, but genetic variance in fitness was estimated to be not signific antly different from zero in all cases. Significant heritability was d etected in both populations for one trait (date of first cleistogamous flower) known to be closely related to fitness on the hillside. In ge neral, heritability was reduced for populations when grown in the hill side site relative to the floodplain site, suggesting that stress acts to reduce the expression of genetic variance and the potential to res pond to selection there. Consistent reductions in heritability associa ted with more stressful environments suggest that populations invading such sites may undergo little adaptive differentiation and be more pr one to local extinction.