Uyenoyama M K, Waller D M
Department of Zoology, Duke University, Durham, North Carolina 27706.
Theor Popul Biol. 1991 Aug;40(1):14-46. doi: 10.1016/0040-5809(91)90045-h.
Simple theories for the evolution of breeding systems suggest that the fate of an allele that modifies the rate of self-fertilization hinges only on the degree to which selfing reduces opportunities for outcrossing ("pollen discounting") and the extent of inbreeding depression. These theories predict that outcrossing evolves whenever deleterious mutations have a more severe effect in combination than expected from their individual effects. We study the evolutionary dynamics of a modifier of the rate of self-fertilization in populations subject to complete pollen discounting and recurrent mutations which impair viability at a single locus in diploids and at two loci in haploids. Our analysis indicates that genetic associations arising immediately upon the introduction of a rare modifier allele generate substantial quantitative and qualitative departures from expectation. Higher rates of segregation under selfing in our one-locus diploid model generate positive associations between enhancers of selfing and wild-type viability alleles, which in turn favor the evolution of selfing under a wider range of conditions than expected. Greater opportunities for recombination under outcrossing in our two-locus haploid model generate positive associations between enhancers of outcrossing and wild-type viability alleles. These associations favor the evolution of outcrossing under a wider range of conditions, and introduce the possibility of stable mixed mating systems involving both selfing and outcrossing. Our explicit analysis of genetic associations between loci affecting viability and the rate of self-fertilization indicates that modifiers that enhance the production of offspring with very high (and very low) viability by promoting segregation or recombination develop positive associations with high viability. This advantage of producing extremes can compensate for an initial disadvantage in offspring number.
关于繁殖系统进化的简单理论表明，一个改变自体受精率的等位基因的命运仅取决于自体受精降低异交机会的程度（“花粉折扣”）以及近亲繁殖衰退的程度。这些理论预测，只要有害突变组合起来产生的影响比其个体影响预期的更严重，异交就会进化。我们研究了在完全花粉折扣和反复发生突变的种群中，自体受精率修饰因子的进化动态，这些突变会损害二倍体中单一位点以及单倍体中两个位点的生存能力。我们的分析表明，引入罕见修饰等位基因后立即产生的遗传关联，在数量和质量上都与预期有很大偏差。在我们的单一位点二倍体模型中，自体受精时更高的分离率会在自体受精增强子和野生型生存能力等位基因之间产生正相关，这反过来又使得自体受精在比预期更广泛的条件下进化。在我们的双位点单倍体模型中，异交时更大的重组机会在异交增强子和野生型生存能力等位基因之间产生正相关。这些关联有利于异交在更广泛的条件下进化，并引入了涉及自体受精和异交的稳定混合交配系统的可能性。我们对影响生存能力和自体受精率的位点之间遗传关联的明确分析表明，通过促进分离或重组来提高具有非常高（和非常低）生存能力后代产量的修饰因子，会与高生存能力产生正相关。产生极端情况的这种优势可以弥补后代数量方面的初始劣势。
