Department of Biology, Indiana University, Bloomington, IN 47405, USA.
Evolution. 2013 Jun;67(6):1591-7. doi: 10.1111/evo.12088. Epub 2013 Apr 4.
Interdemic selection by the differential migration of individuals out from demes of high fitness and into demes of low fitness (Phase III) is one of the most controversial aspects of Wright's Shifting Balance Theory. I derive a relationship between Phase III migration and the interdemic selection differential, S, and show its potential effect on FST . The relationship reveals a diversifying effect of interdemic selection by Phase III migration on the genetic structure of a metapopulation. Using experimental metapopulations, I explored the effect of Phase III migration on FST by comparing the genetic variance among demes for two different patterns of migration: (1) island model migration and (2) Wright's Phase III migration. Although mean migration rates were the same, I found that the variance among demes in migration rate was significantly higher with Phase III than with island model migration. As a result, FST for the frequency of a neutral marker locus was higher with Phase III than it was with island model migration. By increasing FST , Phase III enhanced the genetic differentiation among demes for traits not subject to interdemic selection. This feature makes Wright's process different from individual selection which, by reducing effective population size, decreases the genetic variance within demes for all other traits. I discussed this finding in relation to the efficacy of Phase III and random migration for effecting peak shifts, and the contribution of genes with indirect effects to among-deme variation.
局域种群间的选择——个体从适合度高的局域种群中迁出，进入适合度低的局域种群（第三阶段），这是 Wright 连续平衡理论最具争议的方面之一。我推导出了第三阶段迁移与局域种群间选择差，S 之间的关系，并展示了它对 FST 的潜在影响。该关系揭示了局域种群间选择通过第三阶段迁移对复合种群遗传结构的多样化效应。通过使用实验复合种群，我通过比较两种不同迁移模式下（1）岛屿模型迁移和（2）Wright 的第三阶段迁移，来探究第三阶段迁移对 FST 的影响。尽管平均迁移率相同，但我发现，与岛屿模型迁移相比，第三阶段的迁移率在局域种群之间的方差明显更高。因此，对于中性标记基因座的频率来说，第三阶段的 FST 比岛屿模型迁移的 FST 更高。通过增加 FST ，第三阶段增强了不受局域种群间选择影响的性状的局域种群之间的遗传分化。这一特征使得 Wright 的过程不同于个体选择，后者通过降低有效种群大小，降低了所有其他性状的局域种群内的遗传方差。我讨论了这一发现与第三阶段和随机迁移在产生峰值转移方面的有效性，以及间接效应基因对局域种群间变异的贡献。
