Data from: Phase III of Wright's Shifting Balance Process and the variance among demes in migration rate

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.

由个体从高适合度同类群（deme）迁出、迁入低适合度同类群的差异化迁移所介导的同类群间选择（interdemic selection，阶段III），是赖特移位平衡理论（Wright's Shifting Balance Theory）中最具争议的内容之一。本研究推导了阶段III迁移与同类群间选择差S之间的关系，并阐明了其对群体分化系数（FST）的潜在影响。该关系揭示了阶段III迁移所介导的同类群间选择对集合种群（metapopulation）遗传结构的多样化效应。借助实验集合种群，本研究通过对比两种不同迁移模式下同类群间的遗传方差，探究了阶段III迁移对FST的影响：(1) 岛屿模型迁移（island model migration）；(2) 赖特阶段III迁移。尽管两种模式的平均迁移速率一致，但研究发现，阶段III迁移下同类群间的迁移速率方差显著高于岛屿模型迁移。由此，中性标记基因座（neutral marker locus）频率对应的FST在阶段III迁移模式下也显著高于岛屿模型迁移。通过提升FST，阶段III迁移强化了未受同类群间选择作用的性状在同类群间的遗传分化。这一特征使得赖特的演化过程与个体选择存在本质区别：个体选择会通过降低有效种群大小（effective population size），减小所有其他性状在同类群内部的遗传方差。本研究就阶段III迁移与随机迁移在实现峰位移（peak shifts）方面的有效性，以及具有间接效应的基因对同类群间变异的贡献，对上述发现进行了讨论。