Willis John H
Department of Biology, University of Oregon, Eugene, Oregon, 97403.
Evolution. 1996 Aug;50(4):1501-1511. doi: 10.1111/j.1558-5646.1996.tb03923.x.
When populations are partially inbred due to the population structure or to a mixed mating system like partial self-fertilization, some individuals will be more inbred than others. This heterogeneity among individuals in the history of inbreeding can greatly complicate the interpretation of measures of quantitative genetic variability when the traits studied exhibit inbreeding depression. Partial inbreeding can also bias measures of phenotypic selection toward the detection of strong directional and stabilizing selection. In this paper, data are presented from several inbreeding experiments conducted on two partially selfing, annual populations of the monkeyflower Mimulus guttatus that show that the means of many of the morphological and phenological traits measured were affected by inbreeding. These findings imply that estimates of heritabilities and additive genetic covariances would not reflect the potential for these populations to respond to selection. Phenotypic selection analyses conducted on naturally occurring plants, involving linear regressions of relative seed production on the traits, revealed significant directional selection on many of the same quantitative traits measured in the inbreeding studies. However, when the same selection analyses were performed on plants with known histories of inbreeding, part of the statistical relationship between relative seed number and the traits was found to be due to the mating system: inbred individuals had both lower seed production and different mean values for the traits than outcrossed individuals. It is also shown, with a hypothetical example, that partial inbreeding can bias measures of stabilizing selection toward the detection of strong stabilizing selection. Partial inbreeding therefore tends to make directional and stabilizing selection appear stronger than it is, and it may be that natural selection in the wild is actually weaker than many studies of partially inbred species suggest.
当种群由于种群结构或部分自交等混合交配系统而部分近亲繁殖时，一些个体的近亲繁殖程度会高于其他个体。当所研究的性状表现出近亲繁殖衰退时，个体在近亲繁殖历史上的这种异质性会极大地复杂化对数量遗传变异性度量的解释。部分近亲繁殖还会使表型选择的度量偏向于检测强烈的定向选择和稳定选择。在本文中，展示了对猴面花沟酸浆（Mimulus guttatus）的两个部分自交的一年生种群进行的几个近亲繁殖实验的数据，这些数据表明所测量的许多形态和物候性状的均值受到了近亲繁殖的影响。这些发现意味着遗传力和加性遗传协方差的估计不会反映这些种群对选择作出响应的潜力。对自然生长的植物进行的表型选择分析，涉及相对种子产量对性状的线性回归，揭示了在近亲繁殖研究中所测量的许多相同数量性状上存在显著的定向选择。然而，当对具有已知近亲繁殖历史的植物进行相同的选择分析时，发现相对种子数与性状之间的部分统计关系是由于交配系统造成的：近亲繁殖个体的种子产量较低，并且与杂交个体相比，这些性状的均值也不同。通过一个假设的例子还表明，部分近亲繁殖会使稳定选择的度量偏向于检测强烈的稳定选择。因此，部分近亲繁殖往往会使定向选择和稳定选择看起来比实际更强，并且可能野外的自然选择实际上比许多对部分近亲繁殖物种的研究所表明的要弱。
