Department of Agronomy and Range Science, University of California, Davis, USA.
Theor Appl Genet. 1979 Jul;54(4):181-90. doi: 10.1007/BF00263049.
Several populations of two species of the genus Limnanthes, (L. alba, an outbreeder and L. floccosa, an inbreeder) were examined with respect to variability of fifteen quantitative characters, allozyme variation at 11 loci, and response to different pollination conditions and moisture stress. Nearly equal amounts of phenotypic variability were found in the two species. L. alba had higher within-family variability than L. floccosa, but this result was highly heterogeneous among characters. A study of between- and within-population variance estimates did not reject the null hypothesis that L. alba and L. floccosa are similar with regard to the partitioning and amount of variability for quantitative characters. However, allozyme variation at 11 loci in a large number of populations showed L. alba to be highly polymorphic in contrast to the virtual monomorphism within L. floccosa populations. The average number of alleles per locus in L. alba and L. floccosa was 1.97 and 1.02, respectively, and on an average, L. alba and L. floccosa populations had 63% and 3% loci with polymorphism, respectively. Three groups of allozyme allelic combinations emerged which correlated well with the taxonomic delineation of allogamous L. alba, three semi-autogamous L. floccosa forms and two autogamous L. floccosa forms.All taxa showed a significant reduction in the seed output per plant due to moisture stress. L. alba suffered a further loss of fecundity under the paucity of pollinators, L. floccosa ssp. floccosa showed no significant effect from this factor, whereas L. floccosa ssp. grandiflora exhibited a curvilinear response which peaked at 'partial pollination' and decreased to a lower level at 'full pollination.'The geographic distribution of the two species with regard to the temperature and rainfall distribution did not suggest L. floccosa to be living in drier marginal areas. Patterns of variation in flowering time showed L. alba to be less variable than L. floccosa. Overall, there seemed to be little direct support for the thesis that inbreeding species originated from outcrossing taxa in marginal environments as a direct adaptation to a shortened growing season of xeric environments and to the lack of pollinators. Alternative hypotheses suggest that autogamy in L. floccosa might have evolved as a reproductive isolating barrier acting through either cleistogamy or divergence in flowering times.
两种白头花属（L. alba，杂交种；L. floccosa，自交种）的多个种群在 15 个数量性状、11 个位点的同工酶变异以及对不同传粉条件和水分胁迫的响应方面进行了研究。两种物种的表型变异性几乎相等。L. alba 的家系内变异性高于 L. floccosa，但这一结果在各性状间存在高度异质性。种群间和种群内方差估计的研究并未否定 L. alba 和 L. floccosa 在数量性状的变异划分和变异量方面相似的零假设。然而，在大量种群的 11 个位点的同工酶变异表明，L. alba 高度多态，而 L. floccosa 种群几乎是单态。L. alba 和 L. floccosa 的每个位点的平均等位基因数分别为 1.97 和 1.02，平均而言，L. alba 和 L. floccosa 种群分别有 63%和 3%的位点具有多态性。三组同工酶等位基因组合与异交的 L. alba、三个半自交的 L. floccosa 形式和两个自交的 L. floccosa 形式的分类学划分很好地相关。所有分类群的植物每株种子产量由于水分胁迫而显著减少。L. alba 在传粉者稀少的情况下进一步丧失了繁殖力，L. floccosa ssp. floccosa 没有受到这一因素的显著影响，而 L. floccosa ssp. grandiflora 则表现出曲线响应，在“部分授粉”时达到峰值，在“完全授粉”时下降到较低水平。这两个物种的地理分布与温度和降雨量分布表明，L. floccosa 并不生活在较干燥的边缘地区。开花时间的变异模式表明，L. alba 的变异性小于 L. floccosa。总的来说，几乎没有直接证据支持这样的假设，即自交种是从边缘环境中的异交种进化而来的，这是对干旱环境中生长季节缩短和传粉者缺乏的直接适应。替代假说表明，L. floccosa 中的自交可能是通过闭花受精或开花时间的差异进化而来的，作为一种生殖隔离的屏障。
