Kärkkäinen Katri, Koski Veikko, Savolainen Outi
Department of Genetics, University of Oulu, 90570, Oulu, Finland.
Department of Forest Ecology, Finnish Forest Institute, Box 18, 01301, Vantaa, Finland.
Evolution. 1996 Feb;50(1):111-119. doi: 10.1111/j.1558-5646.1996.tb04477.x.
The magnitude of inbreeding depression caused by recessive mutations in a population is dependent on the mutation rate and on the intensity of selection against the mutations. We studied geographical differences in the level of early inbreeding depression of Scots pine in a common garden experiment. The mean abortion rate of experimentally self-pollinated seeds was significantly lower (75.4%) among trees that originated from northern populations (66-69°N) than among trees from more southern (60-62°N) populations (86.5%). Thus, the number of embryonic lethal equivalents was lower in the northern populations (4.5) than in the southern ones (6.9). The outcrossing rate at the mature seed stage was slightly lower in the northern populations (average 0.93) than in the southern one (0.99). The estimated selfing rate at the zygote stage varied from 0-0.28 in the populations. The reduction in the magnitude of inbreeding depression in the north may have been caused by increased levels of self-fertilization in the northern populations. The proportion of self-fertilized seedlings and adults was very small in all populations (F ≈ 0), indicating high inbreeding depression also in later life stages. The high level of inbreeding depression in the partially selfing Scots pine can be explained by mutation-selection balance only if the mutation rate is high.
一个种群中隐性突变导致的近亲繁殖衰退程度取决于突变率以及针对这些突变的选择强度。我们在一个共同花园实验中研究了苏格兰松早期近亲繁殖衰退水平的地理差异。来自北方种群（北纬66 - 69°）的树木实验自花授粉种子的平均败育率（75.4%）显著低于来自更南方种群（北纬60 - 62°）的树木（86.5%）。因此，北方种群中胚胎致死当量的数量（4.5）低于南方种群（6.9）。北方种群在成熟种子阶段的异交率（平均0.93）略低于南方种群（0.99）。在合子阶段估计的自交率在各种群中从0 - 0.28不等。北方近亲繁殖衰退程度的降低可能是由于北方种群中自花受精水平的提高。所有种群中自花受精的幼苗和成年个体比例都非常小（F≈0），这表明在生命后期阶段也存在高度的近亲繁殖衰退。只有当突变率很高时，部分自交的苏格兰松中高度的近亲繁殖衰退才能用突变 - 选择平衡来解释。
