Data from: Spontaneous mutation accumulation in multiple strains of the green alga, Chlamydomonas reinhardtii

Estimates of mutational parameters, such as the average fitness effect of a new mutation and the rate at which new genetic variation for fitness is created by mutation, are important for the understanding of many biological processes. However, the causes of interspecific variation in mutational parameters and the extent to which they vary within species remain largely unknown. We maintained multiple strains of the unicellular eukaryote Chlamydomonas reinhardtii, for approximately 1000 generations under relaxed selection by transferring a single cell every ∼10 generations. Mean fitness of the lines tended to decline with generations of mutation accumulation whereas mutational variance increased. We did not find any evidence for differences among strains in any of the mutational parameters estimated. The overall change in mean fitness per cell division and rate of input of mutational variance per cell division were more similar to values observed in multicellular organisms than to those in other single-celled microbes. However, after taking into account differences in genome size among species, estimates from multicellular organisms and microbes, including our new estimates from C. reinhardtii, become substantially more similar. Thus, we suggest that variation in genome size is an important determinant of interspecific variation in mutational parameters.

突变参数的估算（包括新突变的平均适合度效应、突变诱导产生适合度相关新遗传变异的速率），对于解析诸多生物学过程至关重要。然而，突变参数的种间变异成因，以及其在物种内部的变异程度，目前学界仍知之甚少。本研究以单细胞真核生物莱茵衣藻（Chlamydomonas reinhardtii）的多个菌株为实验材料，通过每约10代转移单个细胞的方式，在松弛选择条件下连续培养约1000代。结果显示，各实验品系的平均适合度随突变积累代数呈下降趋势，而突变方差水平则随之升高。在所估算的各类突变参数中，未发现不同菌株间存在显著差异的证据。单位细胞分裂对应的平均适合度变化量，以及单位细胞分裂对应的突变方差输入速率，整体上与多细胞生物的观测结果更为接近，而非其他单细胞微生物。然而，在考量物种间基因组大小差异后，多细胞生物与微生物（包括本研究针对莱茵衣藻的新估算结果）的相关参数估算值变得更为相近。据此，我们认为基因组大小的变异是造成突变参数种间差异的重要决定因素。