Kisdi Éva, Geritz Stefan A H
Department of Genetics, Eötvös University, 1088, Budapest, Múzeum krt. 4/A, Hungary.
Department of Zoology, University of Maryland, College Park, Maryland, 20742.
Evolution. 1999 Aug;53(4):993-1008. doi: 10.1111/j.1558-5646.1999.tb04515.x.
We demonstrate how a genetic polymorphism of distinctly different alleles can develop during long-term frequency-dependent evolution in an initially monomorphic diploid population, if mutations have only small phenotypic effect. As a specific example, we use a version of Levene's (1953) soft selection model, where stabilizing selection acts on a continuous trait within each of two habitats. If the optimal phenotypes within the habitats are sufficiently different, then two distinctly different alleles evolve gradually from a single ancestral allele. In a wide range of parameter values, the two locally optimal phenotypes will be realized by one of the homozygotes and the heterozygote, rather than by the two homozygotes. Unlike in the haploid analogue of the model, there can be multiple polymorphic evolutionary attractors with different probabilities of convergence. Our results differ from the population genetic models of short-term evolution in two aspects: (1) a polymorphism that is population genetically stable may be invaded by a new mutant allele and, as a consequence, the population may fall back to monomorphism, (2) long-term evolution by allele substitutions may lead from a population where polymorphism is not possible into one where polymorphism is possible.
我们证明了，如果突变仅具有较小的表型效应，那么在一个初始为单态的二倍体群体中，截然不同的等位基因的遗传多态性如何在长期频率依赖进化过程中形成。作为一个具体例子，我们使用了莱文（1953）的软选择模型的一个版本，其中稳定选择作用于两个栖息地中每个栖息地内的一个连续性状。如果栖息地内的最优表型差异足够大，那么两个截然不同的等位基因会从单个祖先等位基因逐渐进化而来。在广泛的参数值范围内，两个局部最优表型将由其中一个纯合子和杂合子实现，而不是由两个纯合子实现。与该模型的单倍体类似物不同，可能存在多个具有不同收敛概率的多态进化吸引子。我们的结果在两个方面与短期进化的群体遗传模型不同：（1）一个群体遗传上稳定的多态性可能会被一个新的突变等位基因入侵，结果，群体可能会退回到单态，（2）通过等位基因替代的长期进化可能会使一个不可能存在多态性的群体转变为一个可能存在多态性的群体。
