García-Dorado Aurora, González Jorge A
Departamento de Genética, Facultad de Biología, Universidad Complutense, 28040, Madrid, Spain.
Evolution. 1996 Aug;50(4):1573-1578. doi: 10.1111/j.1558-5646.1996.tb03929.x.
Stabilizing selection, which favors intermediate phenotypes, is frequently invoked as the selective force maintaining a population's status quo. Two main alternative reasons for stabilizing selection on a quantitative trait are possible: (1) intermediate trait values can be favored through the causal effect of the trait on fitness (direct stabilizing selection); or (2) through a pleiotropic, deleterious side effect on fitness of mutants affecting the trait (apparent stabilizing selection). Up to now, these alternatives have never been experimentally disentangled. Here we measure fitness as a function of the number of abdominal bristles within four Drosophila melanogaster lines, one with high, one with low, and two with intermediate average bristle number. The four were inbred nonsegregating lines, so that apparent selection due to pleiotropy is not possible. Individual fitness significantly increased (decreased) with bristles number in the low (high) line. No significant fitness-trait association was detected within each intermediate line. These results reveal substantial direct stabilizing selection on the trait.
定向选择有利于中间表型，常被认为是维持种群现状的选择力量。对于数量性状的定向选择，可能有两个主要的替代原因：（1）中间性状值可通过该性状对适合度的因果效应而受到青睐（直接定向选择）；或（2）通过对影响该性状的突变体的适合度产生多效性有害副作用（表观定向选择）。到目前为止，这些替代原因从未通过实验区分开来。在这里，我们在四个黑腹果蝇品系中测量适合度作为腹部刚毛数量的函数，一个品系的刚毛数量高，一个品系的刚毛数量低，另外两个品系的平均刚毛数量处于中间水平。这四个品系是近交非分离品系，因此不可能存在由于多效性导致的表观选择。在低刚毛数量品系中，个体适合度随刚毛数量显著增加（减少）。在每个中间品系中未检测到显著的适合度-性状关联。这些结果揭示了对该性状存在大量直接定向选择。
