Data from: Evolution of haploid–diploid life cycles when haploid and diploid fitnesses are not equal

Many organisms spend a significant portion of their life cycle as haploids and as diploids (a haploid–diploid life cycle). However, the evolutionary processes that could maintain this sort of life cycle are unclear. Most previous models of ploidy evolution have assumed that the fitness effects of new mutations are equal in haploids and homozygous diploids, however, this equivalency is not supported by empirical data. With different mutational effects, the overall (intrinsic) fitness of a haploid would not be equal to that of a diploid after a series of substitution events. Intrinsic fitness differences between haploids and diploids can also arise directly, for example because diploids tend to have larger cell sizes than haploids. Here, we incorporate intrinsic fitness differences into genetic models for the evolution of time spent in the haploid versus diploid phases, in which ploidy affects whether new mutations are masked. Life-cycle evolution can be affected by intrinsic fitness differences between phases, the masking of mutations, or a combination of both. We find parameter ranges where these two selective forces act and show that the balance between them can favor convergence on a haploid–diploid life cycle, which is not observed in the absence of intrinsic fitness differences.诸多生物在其生命周期的相当一部分阶段以单倍体（haploid）和二倍体（diploid）形式存在，即拥有单倍体-二倍体生命周期。然而，能够维持这类生命周期的演化进程目前仍不明确。既往多数倍性演化模型均假设，新突变在单倍体与纯合二倍体（homozygous diploid）中的适合度效应（fitness effect）相等，但这一等价性并未得到实证数据的支持。若突变效应存在差异，经历多轮替换事件（substitution event）后，单倍体的整体内在适合度（intrinsic fitness）将与二倍体不相等。单倍体与二倍体之间的内在适合度差异也可直接产生，例如二倍体的细胞尺寸通常大于单倍体。本研究将内在适合度差异纳入针对单倍体与二倍体阶段时长演化的遗传模型（genetic model）中，该模型中倍性会影响新突变是否被掩盖。生命周期演化可受阶段间内在适合度差异、突变掩盖效应，或二者共同作用的影响。本研究找到了这两种选择压力（selective force）发挥作用的参数范围，并证明二者的平衡可促成单倍体-二倍体生命周期的趋同演化，而这一现象在缺乏内在适合度差异的情况下不会出现。