Heywood John S
Botany Department, University of Texas, Austin, TX, 78712.
Evolution. 1989 Nov;43(7):1387-1397. doi: 10.1111/j.1558-5646.1989.tb02590.x.
The handicap mechanism of sexual selection by female choice has been strongly criticized because it does not cause sexual selection to reinforce viability selection and it cannot account for the origin of mating preferences. However, several models indicate that the handicap mechanism can have important effects when operating in conjunction with Fisher's mechanism in polygynous populations. These models have been criticized because they require that fitness remains heritable indefinitely. I develop a simple haploid model of the handicap mechanism based on nonheritable variation in paternal investment, thus eliminating the problem of heritable fitness. This model produces the same evolutonary dynamics as both simple and quantitative genetic models of the handicap mechanism based on heritable fitness. If the parameters are such that Fisherian runaway selection does not occur in the null model (i.e., the polymorphic equilibria, which lie along the "Fisher line," are stable), then the handicap mechanism turns the Fisher line into an evolutionary trajectory upon which all other trajectories converge. This occurs because Fisher's mechanism generates no net selection on female preference when the population is on the Fisher line, so that any additional source of selection (direct or indirect) on female choice causes the population to evolve deterministically along the Fisher line. This change in the evolutionary dynamics has the important consequence of eliminating the potential for rapid population divergence for mating systems via genetic drift along the Fisher line.
雌性选择导致的性选择的不利条件机制受到了强烈批评，因为它不会使性选择加强生存力选择，也无法解释交配偏好的起源。然而，一些模型表明，在一夫多妻制种群中，当不利条件机制与费舍尔机制共同作用时，可能会产生重要影响。这些模型也受到了批评，因为它们要求适合度能无限期地保持可遗传。我基于父本投资的非遗传变异，开发了一个简单的单倍体不利条件机制模型，从而消除了可遗传适合度的问题。该模型产生的进化动态与基于可遗传适合度的不利条件机制的简单遗传模型和数量遗传模型相同。如果参数设定使得在零模型中不会发生费舍尔失控选择（即沿着“费舍尔线”的多态平衡是稳定的），那么不利条件机制会将费舍尔线转变为一条进化轨迹，所有其他轨迹都会汇聚到这条轨迹上。出现这种情况是因为当种群处于费舍尔线上时，费舍尔机制不会对雌性偏好产生净选择，所以对雌性选择的任何额外选择来源（直接或间接）都会导致种群沿着费舍尔线确定性地进化。进化动态的这种变化具有重要的后果，即消除了通过沿着费舍尔线的遗传漂变实现交配系统快速种群分化的可能性。
