Data from: Fitness consequences of occasional outcrossing in a functionally asexual plant (Oenothera biennis)

Many clonal organisms occasionally outcross, but the long-term consequences of such infrequent events are often unknown. During five years, representing three to five plant generations, we followed 16 experimental field populations of the forb, Oenothera biennis, originally planted with the same 18 original genotypes. Oenothera biennis usually self-fertilizes, which due to its genetic system (Permanent Translocation Heterozygosity), results in seeds that are clones of the maternal plant. However, rare outcrossing produces genetically novel offspring (but without recombination or increased heterozygosity). We sought to understand whether novel genotypes produced through natural outcrossing had greater fecundity or different multigenerational dynamics compared to our original genotypes. We further assessed whether any differences in fitness or abundances through time between original and novel genotypes were exaggerated in the presence versus absence of insect herbivores. Over the course of the experiment, we genotyped >12,500 plants using microsatellite DNA markers to identify and track the frequency of specific genotypes and estimated fecundity on a subset (>3000) of plants. The effective outcrossing rate was 7.3% in the first year and ultimately 50% of the plants were of outcrossed origin by the final year of the experiment. Lifetime fruit production per plant was on average 32% higher across all novel genotypes produced via outcrossing compared to the original genotypes, and this fecundity advantage was significantly enhanced in populations lacking herbivores. Among 43 novel genotypes that were abundant enough to phenotype with replication, plants produced nearly 30% more fruits than the average of their specific two parental genotypes, and marginally more fruits (8%) than their most fecund parent. Mean per capita fecundity of novel genotypes predicted their relative frequencies at the end of the experiment. Novel genotypes increased more dramatically in herbivore-present compared to suppressed populations (45% vs. 27% of all plants), countering the increased competition from dandelions (Taraxacum officinale) that resulted from herbivore suppression. Increased interspecific competition likely also lead to the lower realized fitness of novel versus original genotypes in herbivore-suppressed populations. These results demonstrate that rare outcrossing and the generation of novel genotypes can create high-fecundity progeny, with the biotic environment influencing the dynamical outcome of such advantages.

许多克隆生物（clonal organism）偶尔会发生异交，但这类罕见事件的长期后果往往尚不明确。本研究历时五年，涵盖3至5个植物世代，对16个野外实验种群展开持续监测。这些种群最初由相同的18个原始基因型（genotype）的杂类草（forb）月见草（Oenothera biennis）构建而来。

月见草通常进行自花授粉，由于其特殊的遗传系统——永久易位杂合性（Permanent Translocation Heterozygosity），其产生的种子实为母株的克隆后代。不过，罕见的异交事件会产生具有全新遗传组成的后代（但不会发生重组或提升杂合性）。

本研究旨在探究两个核心问题：其一，通过自然异交产生的全新基因型，其繁殖力或多代动态是否与原始基因型存在差异；其二，在有无昆虫植食者的条件下，原始基因型与新型基因型之间的适合度或种群丰度差异是否会被放大。

实验期间，我们利用微卫星DNA标记（microsatellite DNA marker）对超过12500株植物进行了基因分型，以识别并追踪特定基因型的频率；同时对其中超过3000株植株的繁殖力开展了估算。

实验第一年的有效异交率为7.3%，最终在实验末期，有50%的植株来自异交产生的新型基因型。相较于原始基因型，所有通过异交产生的新型基因型的单株终身结实量平均提升了32%；且这一繁殖力优势在无植食者的种群中更为显著。

在43个丰度足够开展重复表型分析的新型基因型中，其单株结实量较其双亲的平均水平高出近30%，较其繁殖力最高的亲本高出8%（边际显著）。新型基因型的单株平均繁殖力可预测其在实验末期的相对种群频率。

相较于植食者被抑制的种群，植食者存在的种群中新型基因型的占比提升更为显著（分别为45%与27%），这抵消了因植食者抑制而加剧的蒲公英（Taraxacum officinale）种间竞争。增强的种间竞争同样可能导致：在植食者被抑制的种群中，新型基因型的实际适合度低于原始基因型。

本研究结果表明，罕见的异交事件与新型基因型的产生可培育出高繁殖力的后代，而生物环境会影响这类优势带来的动态结果。