Stratton Donald A
Department of Ecology and Evolution, State University of New York, Stony Brook, NY, 11794, USA.
Evolution. 1992 Feb;46(1):107-120. doi: 10.1111/j.1558-5646.1992.tb01988.x.
Genetic variation for seedling and adult fitness components was measured under natural conditions to determine the relative importance of the seedling stage for lifetime fitness in Erigeron annuus. Variation in lifetime reproductive success can result from both the persistent effects of genetic variation expressed among seedlings and from variation in adult fitness components. Analysis of covariance was used to separate the stage specific from the cumulative effects of genetic variance expressed earlier in the life cycle. E. annuus produces seeds through apomixis, which allowed measurement of the fitness of replicate genotypes from germination through the entire life cycle. There were significant differences among genotypes for date of emergence, seedling size, survivorship and fecundity, but heritabilities were low, indicating slow response to selection. For all characters, environmental components of variance were one to two orders of magnitude larger than genetic variance components, resulting in broad sense heritabilities less than 0.1. For seedling size and fecundity, all of the genetic variance was in the form of genotype-environment interactions, often with large negative genetic correlations across environments. In contrast, genotypes differed in mean survivorship through one year, but there were no genotype-environment interactions for viability. Genetic differences in viability were primarily expressed as differences in overwinter survivorship. Genotype × environment interactions among sites and blocks were generated early in the life cycle while the genotype × environment interactions in response to competitive environment (open, annual cover, perennial cover) first appeared in adult fecundity. Genetic variation in lifetime fitness was not significant, despite a fourfold difference in mean fitness among genotypes.
在自然条件下测量了一年蓬幼苗和成年适合度成分的遗传变异，以确定幼苗期对一年蓬终生适合度的相对重要性。终生繁殖成功率的变异可能源于幼苗间表达的遗传变异的持续影响，也源于成年适合度成分的变异。协方差分析用于区分特定阶段效应与生命周期早期表达的遗传方差的累积效应。一年蓬通过无融合生殖产生种子，这使得能够测量从萌发到整个生命周期的重复基因型的适合度。不同基因型在出苗日期、幼苗大小、存活率和繁殖力方面存在显著差异，但遗传力较低，表明对选择的反应缓慢。对于所有性状，环境方差成分比遗传方差成分大1到2个数量级，导致广义遗传力小于0.1。对于幼苗大小和繁殖力，所有遗传方差均以基因型-环境互作的形式存在，且不同环境间常存在较大的负遗传相关性。相比之下，不同基因型在一年中的平均存活率存在差异，但在活力方面不存在基因型-环境互作。活力的遗传差异主要表现为越冬存活率的差异。地点和区组间的基因型×环境互作在生命周期早期产生，而响应竞争环境（开阔地、一年生植被覆盖、多年生植被覆盖）的基因型×环境互作首先出现在成年繁殖力中。尽管不同基因型的平均适合度相差四倍，但终生适合度的遗传变异并不显著。
