CROSSING-DISTANCE EFFECTS IN DELPHINIUM-NELSONII - OUTBREEDING AND INBREEDING DEPRESSION IN PROGENY FITNESS

Depending on its genetic causes, outbreeding depression in quantitativ e characters may occur first in the free-living F-1 generation produce d by a wide cross. In 1981-1985, we generated F-1 progenies by hand-po llinating larkspurs (Delphinium nelsonii) with pollen from 1-m, 3-m, 1 0-m, or 30-m distances. From the spatial genetic structure indicated b y previous electrophoretic and reciprocal transplantation studies, we estimate that these crosses range from being inbred (f approximate to 0.06) to outbred. We planted 594 seeds from 66 maternal sibships under natural conditions. As of 1992, there was strong evidence for both in breeding depression and outbreeding depression. Progeny from intermedi ate crossing distances grew approximately twice as large as more inbre d or outbred progeny in the first 5 yr after planting (P = 0.013, repe ated measures ANOVA), and survived almost 1 yr longer on average (cont rast of 3-m and 10-m treatments versus 1 m and 30 m; P = 0.028, ANOVA) . Twenty maternal sibships produced flowering individuals; only four a nd two of these represented 1-m and 30-m crossing distances, respectiv ely (P = 0.021, G-test). The cumulative fitness of intermediate distan ce sibships averaged about twice that of 1-m sibships, and five to eig ht times that of 30-m sibships (P = 0.017, ANOVA). Thus, even though p rogeny of 1-m crosses were inbred to a degree only about one-eighth th at of selfing, inbreeding depression approximated 50%, and outbreeding depression equaled or exceeded 50% for all fitness components.