Tonsor Stephen J, Kalisz Susan, Fisher Jill, Holtsford Timothy P
Kellogg Biological Station, 3700 Gull Lake Drive, Michigan State University, Hickory Corners, Michigan, 49060.
Department of Botany and Plant Pathology, Department of Zoology, Michigan State University, East Lansing, Michigan, 48824.
Evolution. 1993 Jun;47(3):833-843. doi: 10.1111/j.1558-5646.1993.tb01237.x.
We explored the extent to which the soil seed bank differed genetically and spatially in comparison to two actively growing stages in a natural population of Plantago lanceolata. All seed-bank seeds, seedlings, and adults of P. lanceolata within eight subunits in a larger population were mapped, subjected to starch gel electrophoresis, and allozyme analysis in 1988. Gel electrophoresis was also used to estimate the mating system in two years, 1986 and 1988. The spatial distributions of seeds, seedlings, and adults were highly coincident. Allele frequencies of the dormant seeds differed significantly from those of the adults for four of the five polymorphic loci. In addition, a comparison of the genotype frequencies of the three life-history stages indicated that the seed bank had an excess of homozygotes. Homozygosity, relative to Hardy-Weinberg expectations, decreased during the life cycle (for seed bank, seedlings, and adults respectively: F = 0.19, 0.09, 0.01; F = 0.14, 0.04, -0.12). Spatial genetic differentiation increased sixfold during the life cycle: (for seed bank, seedling and adults: F ∗∗∗ = 0.02, 0.05, 0.12). The apparent selfing rate was 0.01 in 1986 and 0.09 in 1988. These selfing rates are not large enough to account for the elevated homozygosity of the seed bank. Inbreeding depression, overdominance for fitness, and a "temporal Wahlund's effect" are discussed as possible mechanisms that could generate high homozygosity in the seed bank, relative to later life-history stages. In Plantago lanceolata, the influence of the mating system and the "genetic memory" of the seed bank are obscured by the time plants reach the reproductive stage.
我们探究了在披针叶车前草的一个自然种群中，土壤种子库与两个活跃生长阶段相比，在遗传和空间上的差异程度。1988年，对一个较大种群中八个亚单位内的所有披针叶车前草种子库种子、幼苗和成株进行了定位，进行淀粉凝胶电泳和等位酶分析。凝胶电泳还用于估计1986年和1988年这两年的交配系统。种子、幼苗和成株的空间分布高度一致。在五个多态位点中的四个位点上，休眠种子的等位基因频率与成株的等位基因频率存在显著差异。此外，对三个生活史阶段的基因型频率进行比较表明，种子库中纯合子过剩。相对于哈迪-温伯格预期，纯合度在生命周期中降低（种子库、幼苗和成株的F值分别为：0.19、0.09、0.01；F值分别为：0.14、0.04、-0.12）。空间遗传分化在生命周期中增加了六倍：（种子库、幼苗和成株：F*** = 0.02、0.05、0.12）。1986年的表观自交率为0.01，1988年为0.09。这些自交率不足以解释种子库中升高的纯合度。近亲繁殖衰退、适合度的超显性以及“时间性瓦伦德效应”被讨论为可能导致种子库相对于后期生活史阶段具有高纯合度的机制。在披针叶车前草中，当植物达到生殖阶段时，交配系统和种子库的“遗传记忆”的影响变得模糊不清。
