Hamilton J A, Eckert C G
Department of Biology, Queen's University, Kingston, Ontario, Canada.
Mol Ecol. 2007 Apr;16(8):1649-60. doi: 10.1111/j.1365-294X.2007.03241.x.
Species may often exhibit geographic variation in population genetic structure due to contemporary and historical variation in population size and gene flow. Here, we test the predictions that populations on the margins of a species' distribution contain less genetic variation and are more differentiated than populations towards the core of the range by comparing patterns of genetic variation at five microsatellite loci between disjunct and core populations of the perennial, allohexaploid herb Geum triflorum. We sampled nine populations isolated on alvar habitat within the eastern Great Lakes region in North America, habitats that include disjunct populations of several plant species, and compared these to 16 populations sampled from prairie habitat throughout the core of the species' distribution in midwestern Canada and the USA. Alvar populations exhibited much lower within-population diversity and contained only a subset of alleles found in prairie populations. We detected isolation by distance across the species' range and within alvar and prairie regions separately. As predicted, genetic differentiation was higher among alvar populations than among prairie populations, even after controlling for the geographic distance between sampled populations. Low diversity and high differentiation can be accounted for by the greater contemporary spatial isolation of alvar populations. However, the genetic structure of alvar populations may also have been influenced by postglacial range expansion and contraction. Our results are consistent with alvar populations being founded during an expansion of prairie habitat during the warmer, hypsithermal period approximately 5000 bp and subsequently becoming stranded on isolated alvar habitat as the climate grew cooler and wetter.
由于种群大小和基因流的当代及历史变化，物种在种群遗传结构上常常表现出地理变异。在此，我们通过比较多年生异源六倍体草本植物三叶委陵菜（Geum triflorum）间断分布种群和核心种群在五个微卫星位点的遗传变异模式，来检验以下预测：物种分布边缘的种群比分布核心区域的种群遗传变异更少且分化程度更高。我们在北美五大湖地区东部的阿尔瓦栖息地对九个隔离种群进行了采样，这些栖息地包含几种植物的间断分布种群，并将其与从加拿大中西部和美国中西部该物种分布核心区域的草原栖息地采样的16个种群进行比较。阿尔瓦种群的种群内多样性低得多，且仅包含草原种群中发现的部分等位基因。我们分别在整个物种分布范围内以及阿尔瓦和草原区域内检测到了距离隔离。正如预测的那样，即使在控制了采样种群之间的地理距离之后，阿尔瓦种群之间的遗传分化仍高于草原种群。低多样性和高分化可归因于阿尔瓦种群在当代更大的空间隔离。然而，阿尔瓦种群的遗传结构也可能受到冰期后范围扩张和收缩的影响。我们的结果与阿尔瓦种群在约5000年前较温暖的高温期草原栖息地扩张期间形成，随后随着气候变冷变湿而被困在孤立的阿尔瓦栖息地的情况一致。
