van Kleunen Mark, Fischer Markus, Schmid Bernhard
Institut für Umweltwissenschaften, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
Evolution. 2002 Nov;56(11):2168-77.
Allocation to sexual reproduction is an important life-history trait in clonal plants. Different selection pressures between competitive and competition-free environments are likely to result in the evolution of specialized genotypes and to maintain genetic variation in reproductive allocation. Moreover, selection may also result in the evolution of plastic allocation strategies. The necessary prerequisite for evolution, heritable genetic variation, can best be studied with selection experiments. Starting from a base population of 102 replicated genotypes of the clonal herb Ranunculus reptans, we imposed selection on the proportion of flowering rosettes in the absence of competition (base population: mean = 0.391, broad-sense heritability = 0.307). We also selected on the plasticity in this trait in response to competition with a naturally coexisting grass in a parallel experiment (base population: 14% lower mean in the presence of competition, broad-sense heritability = 0.072). After two generations of bidirectional selection, the proportion of flowering rosettes was 26% higher in the high line than in the low line (realized heritability +/- SE = 0.205 +/- 0.017). Moreover, genotypes of the high line had 11% fewer carpels per flower, a 22% lower proportion of rooted rosettes, and a 39% smaller average distance between rosettes within a clone. In the second experiment, we found no significant responses to selection for high and low plasticity in the proportion of flowering rosettes (realized heritability +/- SE = -0.002 +/- 0.013). Our study indicates a high heritability and potential for further evolution of the proportion of flowering rosettes in R. reptans, but not for its plasticity, which may have been fixed by past evolution at its current level. Moreover, our results demonstrate strong genetic correlations between allocation to sexual reproduction and other clonal life-history characteristics.
对有性繁殖的资源分配是克隆植物重要的生活史特征。竞争环境和非竞争环境之间不同的选择压力可能导致特殊基因型的进化，并维持繁殖分配中的遗传变异。此外，选择也可能导致可塑性分配策略的进化。进化的必要前提条件，即可遗传的遗传变异，最好通过选择实验来研究。我们以克隆草本植物匐枝毛茛的102个重复基因型的基础种群为起点，在无竞争条件下对开花莲座叶丛的比例进行选择（基础种群：均值 = 0.391，广义遗传力 = 0.307）。在一项平行实验中，我们还针对该性状在与一种自然共存的禾本科植物竞争时的可塑性进行选择（基础种群：在有竞争时均值低14%，广义遗传力 = 0.072）。经过两代双向选择后，高选择系中开花莲座叶丛的比例比低选择系高26%（实现遗传力±标准误 = 0.205±0.017）。此外，高选择系的基因型每朵花的心皮数少11%，生根莲座叶丛的比例低22%，克隆体内莲座叶丛之间的平均距离小39%。在第二项实验中，我们发现对于开花莲座叶丛比例的高可塑性和低可塑性选择，没有显著的选择响应（实现遗传力±标准误 = -0.002±0.013）。我们的研究表明，匐枝毛茛开花莲座叶丛比例具有高遗传力和进一步进化的潜力，但其可塑性并非如此，可塑性可能已在过去的进化中固定在当前水平。此外，我们的结果表明，有性繁殖资源分配与其他克隆生活史特征之间存在很强的遗传相关性。
