EFFECTS OF HYBRIDIZATION AND INBREEDING ON FITNESS IN PHLOX

The effects of interpopulation hybridization, and self-fertilization and immigration on fitness in Phlox drummondii were analyzed in 5 natural field sites. Germination rates, survivorship to flowering, fecundity, and net reproductive rates (R_o) were determined for planted populations of natives, hybrids, aliens, and the products of one and two generations of self-fertilization. At all sites, seed germination was 36% for natives, 35% for hybrids and 28% for aliens. Survivorship for natives was 50%, compared to 49% for hybrids and 41% for aliens. The mean fecundity was 34, 35, and 39 seeds per plant for natives, hybrids, and aliens, respectively. The R_o of natives averaged 5.2 vs. 6.4 for hybrids and 4.2 aliens. At all the sites, germination averaged 25% for self-1 plants and 19% for self-2 plants compared to 24% for open-pollinated controls. Survivorship progressed from 50% in the controls to 46% in self-1 and 44% in self-2 plants. Seed production per plant averaged 35% in the control vs. 32% in the self-1 and 25% in the self-2 plants. The mean R_o of the control was 3.8 vs. 3.3 in the self-1 and 2.14 in the self-2 plants. Our results demonstrate that the genetic variable may have a substantial effect on plant fitness in the field.