Holsinger K E
Department of Ecology and Evolutionary Biology, U-3043, University of Connecticut, Storrs, CT 06269-3043, USA.
Proc Natl Acad Sci U S A. 2000 Jun 20;97(13):7037-42. doi: 10.1073/pnas.97.13.7037.
Differences in the frequency with which offspring are produced asexually, through self-fertilization and through sexual outcrossing, are a predominant influence on the genetic structure of plant populations. Selfers and asexuals have fewer genotypes within populations than outcrossers with similar allele frequencies, and more genetic diversity in selfers and asexuals is a result of differences among populations than in sexual outcrossers. As a result of reduced levels of diversity, selfers and asexuals may be less able to respond adaptively to changing environments, and because genotypes are not mixed across family lineages, their populations may accumulate deleterious mutations more rapidly. Such differences suggest that selfing and asexual lineages may be evolutionarily short-lived and could explain why they often seem to be of recent origin. Nonetheless, the origin and maintenance of different reproductive modes must be linked to individual-level properties of survival and reproduction. Sexual outcrossers suffer from a cost of outcrossing that arises because they do not contribute to selfed or asexual progeny, whereas selfers and asexuals may contribute to outcrossed progeny. Selfing and asexual reproduction also may allow reproduction when circumstances reduce opportunities for a union of gametes produced by different individuals, a phenomenon known as reproductive assurance. Both the cost of outcrossing and reproductive assurance lead to an over-representation of selfers and asexuals in newly formed progeny, and unless sexual outcrossers are more likely to survive and reproduce, they eventually will be displaced from populations in which a selfing or asexual variant arises.
通过自体受精和有性异交进行无性繁殖产生后代的频率差异，是影响植物种群遗传结构的主要因素。与具有相似等位基因频率的异交植物相比，自交植物和无性繁殖植物种群内的基因型较少，并且自交植物和无性繁殖植物中更多的遗传多样性是种群间差异的结果，而非有性异交植物。由于多样性水平降低，自交植物和无性繁殖植物可能较难对不断变化的环境做出适应性反应，并且由于基因型不会在不同家族谱系间混合，它们的种群可能会更快地积累有害突变。这些差异表明，自交和无性繁殖谱系在进化上可能寿命较短，这也可以解释为什么它们似乎往往是近期才出现的。尽管如此，不同繁殖方式的起源和维持必定与生存和繁殖的个体水平特性相关。有性异交植物会遭受异交成本，因为它们不会产生自交或无性繁殖后代，而自交植物和无性繁殖植物可能会产生异交后代。当环境减少了不同个体产生的配子结合的机会时，自交和无性繁殖也可能实现繁殖，这种现象被称为繁殖保障。异交成本和繁殖保障都会导致自交植物和无性繁殖植物在新形成的后代中占比过高，除非有性异交植物更有可能生存和繁殖，否则它们最终将被出现自交或无性变异的种群所取代。
