Brys R, Jacquemyn H
Division of Plant Ecology and Systematics, Biology Department, University of Leuven, Leuven, Belgium.
Research Institute for Nature and Forest, Brussels, Belgium.
J Evol Biol. 2016 Feb;29(2):352-9. doi: 10.1111/jeb.12787. Epub 2015 Dec 11.
In hermaphroditic plants, theory for mating system evolution predicts that populations will evolve to either complete autonomous selfing (AS) or complete outcrossing, depending on the balance between automatic selection favouring self-fertilization and costs resulting from inbreeding depression (ID). Theory also predicts that selection for selfing can occur rapidly and is driven by purging of genetic load and the loss of ID. Therefore, selfing species are predicted to have low levels of ID or even to suffer from outbreeding depression (OD), whereas predominantly outcrossing species are expected to have high levels of ID. To test these predictions, we related the capacity of AS to the magnitude of early-acting inbreeding or OD in both allogamous and autogamous species of the orchid genus Epipactis. For each species, the level of AS was assessed under controlled greenhouse conditions, whereas hand-pollinations were performed to quantify early costs of inbreeding or OD acting at the level of fruit and seed production. In the autogamous species, the capacity of AS was high (> 0.72), whereas in the allogamous species AS was virtually absent (< 0.10). Consistent with our hypothesis, allogamous Epipactis species had significantly higher total ID (average: 0.46) than autogamous species, which showed severe costs of OD (average: -0.45). Overall, our findings indicate that strong early-acting ID represents an important mechanism that contributes to allogamy in Epipactis, whereas OD may maintain selfing in species that have evolved to complete selfing.
在雌雄同体植物中，交配系统进化理论预测，种群将进化为完全自主自交（AS）或完全异交，这取决于有利于自花受精的自动选择与近亲繁殖衰退（ID）所产生的成本之间的平衡。该理论还预测，对自交的选择可能迅速发生，并且由遗传负荷的清除和近亲繁殖衰退的消失所驱动。因此，预计自交物种的近亲繁殖衰退水平较低，甚至会遭受远交衰退（OD），而主要进行异交的物种预计具有较高水平的近亲繁殖衰退。为了检验这些预测，我们将Epipactis属兰花的异花授粉和自花授粉物种的自主自交能力与早期近亲繁殖或远交衰退的程度联系起来。对于每个物种，在可控的温室条件下评估自主自交水平，同时进行人工授粉以量化在果实和种子生产水平上近亲繁殖或远交衰退的早期成本。在自花授粉物种中，自主自交能力较高（>0.72），而在异花授粉物种中几乎不存在自主自交（<0.10）。与我们的假设一致，异花授粉的Epipactis物种的总近亲繁殖衰退（平均：0.46）显著高于自花授粉物种，后者表现出严重的远交衰退成本（平均：-0.45）。总体而言，我们的研究结果表明，强烈的早期近亲繁殖衰退是促进Epipactis异交的重要机制，而远交衰退可能在已进化为完全自交的物种中维持自交。
