As biodiversity loss accelerates globally, conservation of at-risk species increasingly relies on strategic genetic management to support remnant isolated populations and reintroductions. In endangered plants, the breeding system can provide crucial information on the role of pollinators in successful reproduction and the relative importance of inbreeding and outbreeding depression. We performed controlled crosses to document the breeding system of Erigeron decumbens (Willamette daisy), an endangered plant endemic to western Oregon prairies. Crosses included no pollen addition (to test for autogamy), geitonogamous self-pollination (to test for self-compatibility), between individuals in the same population (local), and between plants from distant populations (separated by ∼90 km). Filled seeds from each treated capitulum were counted, germinated, and grown for 2 y. Pollination treatment had a significant effect on mean seed set but not on mean seed germination. Seed set was ∼5% in both autogamous and self-pollinations, and ∼53% in local and distant crosses. Plants grown from distant crosses (mean ∼65 leaves) outgrew local crosses (∼53 leaves) by 24% in the first year of growth, but no difference was detected in the second year. Willamette daisy is therefore an outcrossing species that relies on insect pollinators for reproduction. In addition, inbreeding depression was not detected in seed germination, while outbreeding resulted in substantial increases in plant size after 1 y. These results suggest that genetic mixing of isolated populations may enhance fitness and population growth in this species, and habitat management could benefit native bees and other pollinators.
Cascadia Prairie-Oak Partnership
Providing coordination for the technical prairie community in the Willamette Valley, Puget Trough, Georgia Basin (WPG) ecoregion and beyond.