Stoeckel Solenn, Grange Jérôme, Fernández-Manjarres Juan F, Bilger Isabelle, Frascaria-Lacoste Nathalie, Mariette Stéphanie
Cemagref, Unité de Recherche 'Ecosystèmes Forestiers', Domaine des Barres, 45290 Nogent-sur-Vernisson, France.
Mol Ecol. 2006 Jul;15(8):2109-18. doi: 10.1111/j.1365-294X.2006.02926.x.
Wild cherry (Prunus avium L.), a partially asexual self-incompatible forest tree, shows heterozygote excess, which is a poorly studied phenomenon. In three natural populations, we found significant heterozygote excess at almost all investigated loci (eight microsatellites and markers for the self-incompatibility locus). We examined four hypotheses to account for this observed heterozygote excess. First, negative F(IS) can result from a lack of selfed progeny in small populations of outcrossing species. A second explanation for negative F(IS) is selection during the life cycle of the most heterozygous individuals. A third explanation is negative assortative mating when reproduction occurs between individuals bearing phenotypes more dissimilar than by chance. The last explanation for negative F(IS) relies on asexual reproduction. Expectations for each hypothesis were tested using empirical data. Patterns of F(IS) differed among loci. Nevertheless, our experimental results did not confirm the small sample size hypothesis. Although one locus is probably under a hitch-hiking effect from the SI locus, we rejected the effect of the self-incompatibility locus for the genome as a whole. Similarly, although one locus showed a clear pattern consistent with the selection of heterozygous individuals, the heterosis effect over the whole genome was rejected. Finally, our results revealed that clonality probably explains significant negative F(IS) in wild cherry populations when considering all individuals. More theoretical effort is needed to develop expectations and hypotheses, and test them in the case of species combining self-incompatibility and partially asexual reproduction.
欧洲甜樱桃（Prunus avium L.）是一种部分无性繁殖的自交不亲和林木，表现出杂合子过剩现象，这是一个研究较少的现象。在三个自然种群中，我们发现几乎在所有调查的位点（八个微卫星和自交不亲和位点的标记）都存在显著的杂合子过剩。我们检验了四种假说来解释这种观察到的杂合子过剩现象。首先，负的F(IS)可能源于异交物种小种群中缺乏自交后代。对负的F(IS)的第二种解释是在最杂合个体的生命周期中存在选择。第三种解释是当表型差异比随机情况更大的个体之间进行繁殖时发生了负选型交配。对负的F(IS)的最后一种解释依赖于无性繁殖。使用实证数据对每个假说的预期进行了检验。F(IS)的模式在不同位点之间存在差异。然而，我们的实验结果并未证实小样本量假说。尽管一个位点可能受到自交不亲和位点的搭便车效应影响，但我们整体上拒绝了自交不亲和位点对基因组的影响。同样，尽管一个位点显示出与杂合个体选择一致的清晰模式，但整体基因组的杂种优势效应被拒绝。最后，我们的结果表明，当考虑所有个体时，克隆性可能解释了欧洲甜樱桃种群中显著的负F(IS)现象。需要更多的理论努力来制定预期和假说，并在结合自交不亲和和部分无性繁殖的物种中对其进行检验。
