Environment-dependence of quantitative genetic parameters in Impatiens pallida

Population response to selection depends on the presence of additive genetic variance for traits under selection. When a population enters an alien environment, environment-induced changes in the expression of genetic variance may occur. These could have large effects on the response to selection. To investigate the environment-dependence of genetic variance, we conducted a reciprocal transplant experiment between two ecotypically differentiated populations of Impatiens pallida using the progeny of a standard mating design. The floodplain site was characterized by high water availability, moderate temperatures, and continuous dense stands of Impatiens. The hillside site was drier, with larger temperature extremes and supported only scattered patches of Impatiens with significantly lower seed production and earlier mortality. Estimates of heritability were low for each of the 13 traits measured in each population and site (range from 0-28%). Additive genetic variance for life-history traits tended to be larger than for morphological traits, but genetic variance in fitness was estimated to be not significantly different from zero in all cases. Significant heritability was detected in both populations for one trait (date of first cleistogamous flower) known to be closely related to fitness on the hillside. In general, heritability was reduced for populations when grown in the hillside site relative to the floodplain site, suggesting that stress acts to reduce the expression of genetic variance and the potential to respond to selection there. Consistent reductions in heritability associated with more stressful environments suggest that populations invading such sites may undergo little adaptive differentiation and be more prone to local extinction.