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The evolution of genetic canalization under fluctuating selection

机译:波动选择下遗传渠道的演变

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If the direction of selection changes from generation to generation, the ability to respond to selection is maladaptive: the response to selection in one generation leads to reduced fitness in the next. Because the response is determined by the amount of genetic variance expressed at the phenotypic level, rapidly fluctuating selection should favor modifier genes that reduce the phenotypic effect of alleles segregating at structural loci underlying the trait. Such reduction in phenotypic expression of genetic variation has been named "genetic canalization." I support this argument with a series of two- and multilocus models with alternating linear selection and Gaussian selection with fluctuating optimum. A canalizing modifier gene affects the fitness of its carriers in three ways: (I) it reduces the phenotypic consequences of genetic response to previous selection; (2) it reduces the genetic response to selection, which is manifested as linkage disequilibrium between the modifier and structural loci; and (3) it reduces the phenotypic variance. The first two effects reduce fitness under directional selection sustained for several generations, but improve fitness when the direction of selection has just been reversed. The net effect tends to favor a canalizing modifier under rapidly fluctuating selection regimes (period of eight generations or less). The third effect improves fitness of the modifier allele if the fitness function is convex and reduces it if the function is concave. Under fluctuating Gaussian selection, the population is more likely to experience the concave portion of the fitness function when selection is stronger. Therefore, only weak to moderately strong fluctuating Gaussian selection favors genetic canalization. This paper considerably broadens the conditions that favor genetic canalization, which so far has only been postulated to evolve under long-term stabilizing selection. [References: 47]
机译:如果选择的方向代代相传,则对选择的响应能力会变得不适应:一代人对选择的反应会导致下一代的适应性降低。由于反应是由表型水平上表达的遗传变异量决定的,因此快速波动的选择应偏向于修饰基因,该基因可减少等位基因在性状结构位点分离的表型效应。遗传变异的表型表达的这种减少被称为“遗传渠化”。我通过一系列具有交替波动的线性选择和最优波动的高斯选择的两点和多点模型来支持这一论点。渠化修饰基因以三种方式影响其携带者的适应性:(I)降低了对先前选择的遗传反应的表型后果; (2)它降低了对选择的遗传反应,表现为修饰子和结构基因座之间的连锁不平衡。 (3)减少了表型差异。前两个效果会降低在连续几代的方向选择下的适应性,但是当选择方向刚刚反转时,则会提高适应性。净效果倾向于在快速变化的选择机制(八代或更少的时期)下使用渠化修饰剂。如果适应度函数是凸的,则第三个效果可改善修饰等位基因的适应度,而如果凹函数,则第三个效果会降低修饰等位基因的适应性。在波动的高斯选择下,选择越强,总体上越有可能经历适应度函数的凹部。因此,只有弱到中等强的波动高斯选择才有利于遗传渠道化。本文极大地拓宽了有利于遗传渠化的条件,到目前为止,只有在长期稳定的选择下,遗传渠才可以进化。 [参考:47]

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