FUTILE SELFING IN THE TREES FUCHSIA EXCORTICATA (ONAGRACEAE) AND SOPHORA MICROPHYLLA (FABACEAE): INBREEDING DEPRESSION OVER 11 YEARS

Mixed mating (producing a mix of selfed and outcrossed seed) is common in flowering plants and is ecologically important because it potentially offers reproductive assurance against pollination failure. However, selfed seed offers no reproductive assurance unless it overcomes inbreeding depression. In trees and other long-lived plants, genetic evidence suggests that selfed seed seldom matures to adulthood, presumably because of severe inbreeding depression. We measured inbreeding depression over 11 yr in two populations each of two New Zealand trees, Fuchsia excorticata and Sophora microphylla, from pollination to germination and performance in both pots and the field. The accumulated inbreeding depression was very high in both cases (F. excorticata: delta = 0.74 and 0.84; S. microphylla: delta = 0.94 and 0.99) and largely late acting, especially in F. excorticata. Fewer than 10% (and <1% in three of the four cases) of the selfs remain; none have yet flowered, and they appear unlikely to do so. Hence, selfing is likely futile in these species. Thus, fruit, seed, and seedling production are not reliable indicators of successful recruitment: a high density of doomed selfed offspring can mask the absence of the outcrossed seedlings needed for adult replacement.