Data from: Effects of population size and isolation on heterosis, mean fitness, and inbreeding depression in a perennial plant

In small isolated populations, genetic drift is expected to increase chance fixation of partly recessive, mildly deleterious mutations, reducing mean fitness and inbreeding depression within populations and increasing heterosis in outcrosses between populations. We estimated relative effective sizes and migration among populations and compared mean fitness, heterosis, and inbreeding depression for eight large and eight small populations of a perennial plant on the basis of fitness of progeny produced by hand pollinations within and between populations. Migration was limited, and, consistent with expectations for drift, mean fitness was 68% lower in small populations; heterosis was significantly greater for small (mean = 70%, SE = 14) than for large populations (mean = 7%, SE = 27); and inbreeding depression was lower, although not significantly so, in small (mean = )0.29%, SE = 28) than in large (mean = 0.28%, SE = 23) populations. Genetic drift promotes fixation of deleterious mutations in small populations, which could threaten their persistence. Limited migration will exacerbate drift, but data on migration and effective population sizes in natural populations are scarce. Theory incorporating realistic vari- ation in population size and patterns of migration could better predict genetic threats to small population persistence.

在小型隔离种群中，遗传漂变（genetic drift）预期会提升部分隐性、轻度有害突变的随机固定概率，降低种群内的平均适合度与近交衰退（inbreeding depression），并提升种群间异交的杂种优势（heterosis）。我们针对一种多年生植物（perennial plant）的8个大种群与8个小种群，基于种群内及种群间人工授粉（hand pollinations）产生的子代适合度，估算了各群体的相对有效种群大小与种群间迁移率，并比较了它们的平均适合度、杂种优势与近交衰退。研究结果显示种群间迁移受限，且与遗传漂变的理论预期一致：小种群的平均适合度较对照组降低68%；小种群的杂种优势（均值=70%，标准误SE=14）显著高于大种群（均值=7%，SE=27）；而小种群的近交衰退（均值=0.29%，SE=28）虽低于大种群（均值=0.28%，SE=23），但未达到显著水平。遗传漂变会促进有害突变在小种群中固定，这可能对种群存续构成威胁。有限的迁移会加剧遗传漂变的效应，但目前自然种群中关于迁移率与有效种群大小的实测数据仍较为匮乏。将种群大小的现实变异与迁移模式纳入考量的理论模型，能够更精准地预测小型种群存续所面临的遗传威胁。