Effect of environment on the magnitude of inbreeding depression in seed germination in a partially self-fertile perennial herb (Blandfordia grandiflora, Liliaceae)

Inbreeding depression, the decreased fitness of progeny derived from self-fertilization compared to outcrossing, is affected by the environmental conditions in which it is examined, often being greater in adverse environments than in benign environments. We germinated selfed and outcrossed seeds from the same Blandfordia grandiflora plants and estimated inbreeding depression in germination under benign laboratory conditions and adverse field conditions. In both environments, more outcrossed seeds germinated than did selfed seeds. In the laboratory, only 7.7% more outcrossed seeds germinated than did selfed seeds (98.4% ± 0.6 vs. 90.7% ± 3.9), whereas in the field the difference was 22.1% (92.5% ± 1.9 vs. 70.4% ± 5.0). The decrease in germination between the laboratory and field was only 5.9% for outcrossed seeds, but was 20.8% for selfed seeds. Germination of selfed seeds was more variable than of outcrossed seeds in both environments (coefficients of variation, selfed seeds vs. outcrossed seeds: laboratory, 13.6% vs. 1.9%; field, 22.5% vs. 6.5%). Germination success varied significantly among maternal plants, except for outcrossed seeds in the laboratory. In the laboratory, 60% of plants expressed inbreeding depression, whereas in the field all plants expressed inbreeding depression. The magnitude of inbreeding depression was significantly greater in the field than in the laboratory (0.242 ± 0.156 vs. 0.078 ± 0.130). Inbreeding depression of individual plants was positively related between the two environments (r = 0.69). The greater inbreeding depression in the field indicated that selfed seeds were unable to cope with the physiological demands that were imposed by the more adverse field environment.