Jacquemyn Hans, Brys Rein
KU Leuven, Biology Department, Plant Conservation and Population Biology, Kasteelpark Arenberg 31, B-3001 Heverlee, Belgium.
Am J Bot. 2015 Jan;102(1):67-72. doi: 10.3732/ajb.1400449. Epub 2014 Dec 22.
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Although rewarding orchids are believed to have a high pollination efficiency, pollination success is often low, suggesting that rewarding orchids may be prone to pollen limitation. Assuming that selfing contributes significantly to fruit and seed set (i.e., reproductive assurance) and that the quality of selfed seeds is high (i.e., low inbreeding depression), it can be hypothesized that under these circumstances populations evolve to facultative or even complete self-pollination.•
In this study, we performed emasculation and pollen supplementation experiments in the field to assess the extent of outcross pollen limitation and the contribution of autonomous self-pollination to fruit and seed set in the rewarding orchid Epipactis palustris. Hand-pollinations using cross and self-pollen were performed in the greenhouse to investigate the impact of selfing on seed set and seed quality and to assess the magnitude of inbreeding depression.•
Fruit set under natural conditions was high: ca. 70% of all flowers set fruit. Percentage fruit set of emasculated plants was 56%, implying that fruit set in about 14% of all flowers was the result of autonomous self-pollination. Pollen supplementation significantly increased fruit and seed set, indicating strong outcross pollen limitation. Hand-pollination with cross pollen resulted in significantly higher seed set and seed quality compared with manual self-pollination, indicating high levels of early inbreeding depression (δ = 0.46 ± 0.08).•
Overall, these results indicate that, despite the high pollination efficiency, populations of this rewarding orchid species were strongly pollen limited. Costs of early inbreeding depression, on the other hand, were high, which may prevent rapid evolution of complete selfing.
尽管人们认为有回报的兰花具有较高的授粉效率，但授粉成功率往往较低，这表明有回报的兰花可能容易受到花粉限制。假设自交对果实和种子的形成有显著贡献（即生殖保障），并且自交种子的质量较高（即近亲繁殖衰退程度较低），那么可以推测在这些情况下，种群会进化为兼性甚至完全自花授粉。
在本研究中，我们在野外进行了去雄和花粉补充实验，以评估异交花粉限制的程度以及自主自花授粉对有回报的兰花沼生羊耳蒜果实和种子形成的贡献。在温室中进行了使用杂交花粉和自花花粉的人工授粉，以研究自交对种子形成和种子质量的影响，并评估近亲繁殖衰退的程度。
自然条件下的坐果率很高：约70%的花朵都能结果。去雄植株的坐果率为56%，这意味着约14%的花朵坐果是自主自花授粉的结果。补充花粉显著提高了果实和种子的形成，表明存在强烈的异交花粉限制。与人工自花授粉相比，用杂交花粉进行人工授粉导致种子形成率和种子质量显著更高，表明早期近亲繁殖衰退程度较高（δ = 0.46 ± 0.08）。
总体而言，这些结果表明，尽管授粉效率较高，但这种有回报的兰花种群受到了强烈的花粉限制。另一方面，早期近亲繁殖衰退的代价很高，这可能会阻止完全自交的快速进化。
