Rankin Anne E, Weller Stephen G, Sakai Ann K
Department of Ecology and Evolutionary Biology, University of California, Irvine 92697, USA.
Evolution. 2002 Aug;56(8):1574-85. doi: 10.1111/j.0014-3820.2002.tb01469.x.
We investigated inbreeding depression and selfing in hermaphroditic Schiedea menziesii to assess the stability of the breeding system. A combination of high selfing rates and strong inbreeding depression suggests that the mating system is unstable. The population-level selfing rate measured in three years ranged considerably from 0.425 (SE = 0.138) to 0.704 (0.048); family measures of selfing rate varied from zero to one in all three years. Inbreeding coefficients did not differ from zero, suggesting that inbred plants do not survive to reproduction in the field. Average inbreeding depression measured in two greenhouse experiments was 0.608-0.870, with values for individual plants ranging from -0.170 to 0.940. The magnitude of inbreeding depression expressed at different life-history stages depended on experimental conditions. When plants were grown during the winter, inbreeding depression was expressed at early and late life-history stages. When plants were grown during the summer, inbreeding depression was detected for germination but not for later life-history stages. Inbreeding depression for vegetative and inflorescence biomass was also measured using field-collected seeds where cross status was assigned using genotypes determined electrophoretically. We did not detect a relation between inbreeding depression and the selfing rate at the level of the individual plant. We saw no evidence for intrafloral selfing, suggesting that the evolution of increased selfing through autogamy is unlikely, despite high selfing rates. A more likely outcome of breeding system instability is the evolution of gynodioecy, which occurs in species of Schiedea closely related to S. menziesii. Females have been detected in progeny of S. menziesii that have been raised in the greenhouse. In the absence of biotic pollen vectors, the failure of these females to establish in the natural population may result from the absence of adaptations for wind pollination.
我们研究了雌雄同体的门氏施密草中的近亲繁殖衰退和自交现象，以评估其繁殖系统的稳定性。高自交率和强烈的近亲繁殖衰退表明该交配系统不稳定。三年中测得的种群水平自交率差异很大，从0.425（标准误=0.138）到0.704（0.048）；所有三年中自交率的家系测量值从零到一不等。近亲繁殖系数与零无差异，这表明近亲繁殖的植物在野外无法存活到繁殖阶段。在两个温室实验中测得的平均近亲繁殖衰退为0.608 - 0.870，单株植物的值在-0.170到0.940之间。在不同生活史阶段表现出的近亲繁殖衰退程度取决于实验条件。当植物在冬季生长时，近亲繁殖衰退在生活史的早期和晚期阶段表现出来。当植物在夏季生长时，仅在萌发时检测到近亲繁殖衰退，而在后期生活史阶段未检测到。还使用田间采集的种子测量了营养体和花序生物量的近亲繁殖衰退，其中通过电泳确定的基因型来确定杂交状态。我们在单株植物水平上未检测到近亲繁殖衰退与自交率之间的关系。我们没有发现花内自交的证据，这表明尽管自交率很高，但通过自花授粉增加自交的进化不太可能。繁殖系统不稳定更可能的结果是雌全异株的进化，这在与门氏施密草密切相关的施密草属物种中出现。在温室中培育的门氏施密草后代中已检测到雌性植株。在没有生物传粉媒介的情况下，这些雌性植株未能在自然种群中建立可能是由于缺乏对风媒传粉的适应性。
