Data from: Genetic estimates of population age in the water flea, Daphnia magna

Genetic datasets can be used to date evolutionary events, even on recent time scales if sufficient data are available. We used statistics calculated from multilocus microsatellite datasets to estimate population ages in data generated through coalescent simulations and in samples from populations of known age in a metapopulation of Daphnia magna in Finland. Our simulation results show that age estimates improve with additional loci and define a time frame over which these statistics are most useful. On the most recent time scales, assumptions regarding the model of mutation (infinite sites vs. stepwise mutation) have little influence on estimated ages. In older populations, size homoplasy among microsatellite alleles results in a downwards bias for estimates based on the infinite sites model. In the Finnish D. magna metapopulation, our genetically derived estimated ages were biased upwards. Potential sources of this bias include: the underlying model of mutation, gene flow, founder size, and the possibility of persistent source populations in the system. Our simulated data show that genetic age estimation is possible, even for very young populations, but our empirical data highlight the importance of factors such as migration and founding size when these statistics are applied in natural populations.

遗传数据集可用于进化事件的定年，若数据量充足，即便针对极近的时间尺度亦可实现该目标。本研究借助多位点微卫星（multilocus microsatellite）数据集计算得到的统计量，对溯祖模拟（coalescent simulations）生成的数据，以及芬兰大型溞（Daphnia magna）集合种群中已知年龄的种群样本开展了种群年龄估算。模拟结果显示，随着位点数量增加，年龄估算的精度得以提升，同时本研究明确了此类统计量发挥最优效用的时间窗口。在极近的时间尺度下，关于两类突变模型的假设——无限位点模型（infinite sites model）与逐步突变模型（stepwise mutation model）——对年龄估算结果几乎无影响。在老龄种群中，微卫星等位基因间的大小同态现象会导致基于无限位点模型的年龄估算结果出现向下偏差。在芬兰的大型溞集合种群中，本研究通过遗传学方法得到的年龄估算结果存在向上偏差。造成该偏差的潜在来源包括：底层突变模型、基因流、奠基者种群大小，以及研究系统中存在持久源种群的可能性。本研究的模拟数据表明，即便针对极为年轻的种群，遗传年龄估算也具备可行性；但实证数据则凸显出，将此类统计量应用于自然种群时，迁移与奠基者大小等因素的重要性不容忽视。