Data from: Inter-population variation in mating system and late-stage inbreeding depression in Magnolia stellata

Inbreeding has the potential to cause evolutionary changes in populations, although these changes are likely to drive populations to extinction through inbreeding depression and reductions in genetic diversity. We investigated the mating system and late-stage inbreeding depression (δ) in 10 populations of Magnolia stellata using nine microsatellite markers and evaluated the effects of population size and the degree of population isolation through inbreeding and inbreeding depression on the persistence of populations. The outcrossing rates were very similar (~0.7) among populations, but the correlations of paternity, fractions of biparental inbreeding and inbreeding coefficients at the seed stage (FS) varied among populations, suggesting that the level of outcrossing was similar among populations, while the quality of it was not. A significant negative correlation was detected between FS and population size. The average value of δ was 0.709, and the values in six of the 10 populations were significant. The values of δ differed among populations, although clear relationships with population size and the degree of population isolation were not detected. However, in one population, which was very small and located in the edge of the species' range, we obtained a very low value of δ (-0.096), which may be indicative of purging or the fixation of deleterious alleles. Existing M. stellata populations that are small (and thus might be expected to have higher frequencies of inbreeding) and have large values of δ may be in danger of declining, even if the populations are located within the central region of the species range.

近交有可能引发种群的进化改变，但这类改变往往会通过近交衰退（inbreeding depression）与遗传多样性丧失，推动种群走向灭绝。本研究以9个微卫星标记（microsatellite markers）为分析工具，对10个星花木兰（Magnolia stellata）种群的交配系统与晚期近交衰退（δ）展开了调查，并基于近交与近交衰退效应，评估了种群大小、种群隔离程度对种群存续的影响。不同种群间的异交率（outcrossing rates）极为相近，均值约为0.7，但父本相关性、双亲近交比例以及种子阶段近交系数（FS）则存在显著的种群间差异，这表明尽管各群的异交水平相似，但其异交质量却并非一致。研究发现种子阶段近交系数（FS）与种群大小间存在显著负相关关系。晚期近交衰退（δ）的平均值为0.709，10个种群中有6个种群的δ值具有统计学显著性。尽管未检测到δ值与种群大小、种群隔离程度间存在明确关联，但不同种群的δ值仍存在显著差异。不过，在一个体型极小且分布于该物种种群分布范围边缘的种群中，我们测得的δ值极低（-0.096），这或许暗示存在遗传净化（purging）或有害等位基因（deleterious alleles）固定现象。即便位于该物种分布范围的核心区域，那些体型较小（因此预计近交频率更高）且δ值较高的现存星花木兰种群，也可能面临种群衰退的风险。