Kirkpatrick Mark, Price Trevor, Arnold Stevan J
Department of Zoology, University of Texas, Austin, TX, 78712.
Department of Biology C-016, University of California at San Diego, La Jolla, CA, 92093.
Evolution. 1990 Feb;44(1):180-193. doi: 10.1111/j.1558-5646.1990.tb04288.x.
Males of monogamous birds often show secondary sexual traits that are conspicuous but considerably less extreme than those of polygynous species. We develop a quantitative-genetic model for the joint evolution of a male secondary sexual trait, a female mating preference, and female breeding date, following a theory proposed by Darwin and Fisher. Good nutritional condition is postulated to cause females to breed early and to have high fecundity. The most-preferred males are mated by early-breeding females and receive a sexual-selection advantage from those females' greater reproductive success. Results show that conspicuous male traits that decrease survival can evolve but suggest that the extent of maladaptive evolution is greatly limited relative to what is possible in a polygynous mating system for two reasons. First, in the absence of direct fitness effects of mate choice on the female, the equilibria for the male trait and female preference form a curve whose shape shows that the maximum possible strength of sexual selection on males (and hence the potential for maladaptive evolution) is constrained. Under certain conditions, a segment of the equilibrium curve may become unstable, leading to two alternative stable states for the male trait. Second, male parental care will often favor the evolution of mating preferences for less conspicuous males. We also find that sexual selection can appear in the absence of the nutritional effects emphasized by Darwin and Fisher. A review of the literature suggests that the assumptions of the Darwin-Fisher mechanism may often be met in monogamous birds and that other mechanisms may often reinforce it by producing additional components of sexual selection.
一夫一妻制鸟类的雄性通常具有明显的第二性征，但比多配偶制物种的第二性征要温和得多。我们根据达尔文和费希尔提出的理论，建立了一个定量遗传模型，用于研究雄性第二性征、雌性交配偏好和雌性繁殖日期的联合进化。假设良好的营养状况会使雌性提前繁殖并具有高繁殖力。最受青睐的雄性会与早繁殖的雌性交配，并从这些雌性更高的繁殖成功率中获得性选择优势。结果表明，降低生存能力的明显雄性特征可以进化，但也表明，相对于多配偶制交配系统而言，适应不良进化的程度受到极大限制，原因有两个。首先，在配偶选择对雌性没有直接适应性影响的情况下，雄性特征和雌性偏好的平衡点形成一条曲线，其形状表明雄性性选择的最大可能强度（从而适应不良进化的潜力）受到限制。在某些条件下，平衡曲线的一部分可能变得不稳定，导致雄性特征出现两种替代的稳定状态。其次，雄性亲代抚育通常有利于对不太显眼的雄性产生交配偏好的进化。我们还发现，在没有达尔文和费希尔所强调的营养效应的情况下，性选择也可能出现。对文献的回顾表明，达尔文 - 费希尔机制的假设在一夫一妻制鸟类中可能经常得到满足，并且其他机制可能经常通过产生额外的性选择成分来强化它。
