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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 2—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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© 2002 Delbert Wiens, Loreen Allphin, Donald H. Mansfield, and Glenn Thackray

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