Department of Biology, University of Lund, Sölvegatan 37, S-223 62 Lund, Sweden.
Ann Bot. 2013 Sep;112(5):947-55. doi: 10.1093/aob/mct158. Epub 2013 Aug 1.
A shift from outcrossing to selfing is thought to reduce the long-term survival of populations by decreasing the genetic variation necessary for adaptation to novel ecological conditions. However, theory also predicts an increase in adaptive potential as more of the existing variation becomes expressed as homozygous genotypes. So far, relatively few studies have examined how a transition to selfing simultaneously affects means, variances and covariances for characters that might be under stabilizing selection for a spatially varying optimum, e.g. characters describing leaf morphology.
Experimental crosses within an initially self-sterile population of Crepis tectorum were performed to produce an outbred and inbred progeny population to assess how a shift to selfing affects the adaptive potential for measures of leaf morphology, with special emphasis on the degree of leaf dissection, a major target of diversifying selection within the study species.
Three consecutive generations of selfing had a minor impact on survival, the total number of heads produced and the mean leaf phenotype, but caused a proportional increase in the genetic (co)variance matrix for foliar characters. For the degree of leaf dissection, the lowest 50th percentile of the inbred progeny population showed a disproportionate increase in the genetic variance, consistent with the recessive nature of the weakly lobed phenotype observed in interpopulation crosses. Comparison of inbreeding response with large-scale patterns of variation indicates a potential for selection in a (recently) inbred population to drive a large evolutionary reduction in degree of leaf dissection by increasing the frequency of particular sibling lines.
The results point to a positive role for inbreeding in phenotypic evolution, at least during or immediately after a rapid shift in mating system.
从异交向自交的转变被认为会降低种群的长期生存能力，因为这会减少适应新生态条件所需的遗传变异。然而，理论也预测，随着更多的现有变异表达为纯合基因型，适应性潜力会增加。到目前为止，相对较少的研究考察了向自交的转变如何同时影响那些可能受到空间变化最优值稳定选择的特征的平均值、方差和协方差，例如描述叶形态的特征。
在最初自交不育的欧亚蒲公英种群内进行了实验杂交，产生了一个异交和自交的后代群体，以评估向自交转变如何影响叶形态测量的适应潜力，特别强调了叶分裂程度，这是研究物种内多样化选择的主要目标。
连续三代自交对存活率、产生的总头数和平均叶片表型的影响较小，但导致叶片特征的遗传（协）方差矩阵成比例增加。对于叶片分裂程度，自交后代群体的最低 50 百分位数表现出遗传方差的不成比例增加，这与在种群间杂交中观察到的弱裂片表型的隐性性质一致。自交响应与大规模变异模式的比较表明，在（最近）自交种群中，选择有可能通过增加特定的同胞系频率，驱动叶片分裂程度的大进化减少。
结果表明，自交在表型进化中至少在交配系统快速转变期间或之后立即发挥了积极作用。
