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Developmental Failure and Loss of Reproductive Capacity as a Factor in Extinction: A Nine-Year Study of Dedeckera Eurekensis (Polygonaceae)

Abstract

Many long-lived perennial species exhibit lowered reproductive capacity. Early studies of reproductive success in Dedeckera eurekensis (Polygonaceae) demonstrated that the species exhibited extremely low reproductive success, low seed/ovule (S/O) ratios (i.e., the percentage of ovules that produce filled seeds; 2.5 %), low germinability of filled seeds (3.5%), low seedling survivorship (11 .1%), and lack of recruitment in natural populations. These results were attributed to genetic load, but this elicited controversy, prompting long-term studies of the relationship between the S/O ratio and environment. After nine years of monitoring, however, the S/O ratio had not changed significantly (2 .7%), and there was no significant correlation between precipitation and the S/O ratio. Controlled field experiments demonstrated that neither resource availability nor other ecological factors significantly influenced embryo abortion rates. Controlled self-pollinations (N = 115) matured only one questionably filled seed, whereas intrapopulation cross-pollinations (N = 192) produced significantly more seed (S/O = 12.0 %). Previous pollination studies demonstrated that the species has no primary pollinators and is only rarely visited by a few generalist insects. However, the flowers typically self-pollinate in 2β€”3 days following anthesis. Strong inference suggests that the loss of reproductive capacity in D. eurekensis may be the result of inbreeding depression due to the superimposition of self-pollination on a normally outcrossed species carrying a high genetic/segregational load

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