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）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），并提升种群间异交产生的杂种优势（heterosis）。我们以一种多年生植物的8个大种群与8个小种群为研究对象，基于种群内与种群间人工授粉产生的子代适合度，估算了各群体的相对有效种群大小以及种群间的迁移水平，并对比了平均适合度、杂种优势与近交衰退。研究发现种群间迁移受限，且与遗传漂变的预期相符：小种群的平均适合度较对照降低68%；小种群的杂种优势显著高于大种群，其均值为70%、标准误（SE）为14，而大种群的杂种优势均值为7%、标准误为27；小种群的近交衰退水平虽未达显著差异，但略低于大种群，小种群近交衰退均值为0.29%、标准误为28，大种群则为0.28%、标准误为23。遗传漂变会促使有害突变得以在小种群中固定，这可能对种群存续构成威胁。种群间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与有效种群大小的相关数据仍较为匮乏。纳入种群大小与迁移模式真实变异的理论模型，可更精准地预测小型种群存续面临的遗传威胁。