Morris Ashley B, Baucom Regina S, Cruzan Mitchell B
Department of Botany and.
Am J Bot. 2002 Jan;89(1):29-36. doi: 10.3732/ajb.89.1.29.
Persistent seed banks may provide information on historical changes in the genetic composition of populations. We used stratified sampling of the soil seed bank of Astragalus bibullatus (Pyne's ground plum) to assess levels of temporal variation in population genetic structure and to infer historical changes in the levels of inbreeding and relative gene flow. This species has an extremely limited distribution in the Central Basin of Tennessee, where it is found in open areas and along the edges of cedar glades. Protein electrophoresis was conducted on seedlings grown from seeds that had been recovered from three successive 1 cm thick layers of soil sampled from six sites. Analyses of seven polymorphic allozyme loci indicated that there were substantial levels of genetic differentiation among soil layers and sites. Higher levels of genetic diversity were found in seed than in vegetative populations that had been sampled in a previous study. Seed populations from the uppermost soil layer had higher heterozygote deficiencies, displayed higher levels of differentiation among sites, and had higher private allele frequencies than seed populations from the lower two layers. The change in heterozygosity and distribution of genetic variation among sites for the youngest soil layer is consistent with a pattern of increased selfing, sib mating, and decreased gene flow among populations. These changes in inbreeding and relative levels of gene flow are corroborated by information on historical land use practices in the region and support the hypothesis that loss of appropriate habitat has led to smaller population sizes and a more fragmented distribution of this cedar glade endemic.
持久种子库可能提供有关种群遗传组成历史变化的信息。我们对胀果紫云英（派恩氏地李）的土壤种子库进行分层抽样，以评估种群遗传结构的时间变化水平，并推断近亲繁殖水平和相对基因流的历史变化。该物种在田纳西州中部盆地的分布极为有限，生长于开阔地带以及雪松沼泽边缘。对从六个地点采集的连续三层1厘米厚土壤中回收的种子培育出的幼苗进行了蛋白质电泳分析。对七个多态性等位酶位点的分析表明，土壤层和地点之间存在显著的遗传分化。与之前研究中采样的营养体种群相比，种子中发现了更高水平的遗传多样性。最上层土壤层的种子种群比下面两层的种子种群具有更高的杂合子缺陷，位点间分化水平更高，且私有等位基因频率更高。最年轻土壤层的杂合度变化和位点间遗传变异分布与自交、同胞交配增加以及种群间基因流减少的模式一致。该地区历史土地利用实践的信息证实了近亲繁殖和相对基因流水平的这些变化，并支持了以下假设：适宜栖息地的丧失导致了种群规模减小以及这种雪松沼泽特有植物的分布更加碎片化。
