Li Y, Akimoto S
Department of Ecology and Systematics, Graduate School of Agriculture, Hokkaido University, Sapporo, Japan.
J Evol Biol. 2017 Jul;30(7):1347-1360. doi: 10.1111/jeb.13107. Epub 2017 May 19.
Frequency-dependent selection is a fundamental principle of adaptive sex ratio evolution in all sex ratio theories but has rarely been detected in the wild. Through long-term censuses, we confirmed large fluctuations in the population sex ratio of the aphid Prociphilus oriens and detected frequency-dependent selection acting on these fluctuations. Fluctuations in the population sex ratio were partly attributable to climatic factors during the growing season. Climatic factors likely affected the growth conditions of host plants, which in turn led to yearly fluctuations in maternal conditions and sex ratios. In the process of frequency-dependent selection, female proportion higher or lower than ca. 60% was associated with a reduction or increase in female proportion, respectively, the next year. The rearing of aphid clones in the laboratory indicated that mothers of each clone produced an increasing number of females as maternal size increased. However, the mean male number was not related to maternal size, but varied largely among clones. Given genetic variance in the ability to produce males among clones, selection should favour clones that can produce more numerous males in years with a high female proportion. Population-level sex allocation to females was on average 71%-73% for three localities and more female-biased when maternal conditions were better. This tendency was accounted for by the hypothesis of competition among foundresses rather than the hypothesis of local mate competition. We conclude that despite consistent operation of frequency-dependent selection, the sex ratio continues to fluctuate because environmental conditions always push it away from equilibrium.
频率依赖选择是所有性别比例理论中适应性性别比例进化的一个基本原则，但在野外很少被检测到。通过长期普查，我们证实了蚜虫梨长管蚜种群性别比例的大幅波动，并检测到频率依赖选择作用于这些波动。种群性别比例的波动部分归因于生长季节的气候因素。气候因素可能影响了寄主植物的生长条件，进而导致母体条件和性别比例的年度波动。在频率依赖选择过程中，高于或低于约60%的雌性比例分别与次年雌性比例的降低或增加相关。在实验室中饲养蚜虫克隆体表明，随着母体体型的增加，每个克隆体的母体产生的雌性数量增多。然而，平均雄性数量与母体体型无关，但在克隆体之间差异很大。鉴于克隆体之间产生雄性能力的遗传差异，选择应有利于在雌性比例高的年份能产生更多雄性的克隆体。三个地点对雌性的种群水平性别分配平均为71%-73%，当母体条件更好时，性别比例更偏向雌性。这种趋势是由雌虫之间竞争的假设而非本地配偶竞争的假设来解释的。我们得出结论，尽管频率依赖选择持续起作用，但性别比例仍在波动，因为环境条件总是使其偏离平衡。
