Fehlberg Shannon D, Ranker Tom A
Desert Botanical Garden, 1201 N. Galvin Pkwy., Phoenix, AZ 85008-3437, USA.
Mol Phylogenet Evol. 2009 Feb;50(2):326-35. doi: 10.1016/j.ympev.2008.11.011. Epub 2008 Nov 27.
Pleistocene glaciations have had a profound influence on the genetic structure of plant species throughout the Northern Hemisphere because of range contractions, fragmentations, and expansions. Phylogeographic studies have contributed to our knowledge of this influence in several geographic regions of North America, however, very few phylogeographic studies have examined plant species in the Sonoran, Mojave, and Peninsular deserts. In this study, we used sequence data from the chloroplast DNA psbA-trnH intergenic spacer to obtain information on phylogeographic patterns among 310 individuals from 21 populations of Encelia farinosa ("brittlebush"; Asteraceae) across its range. We applied several population and spatial genetic analyses that allowed us to interpret our data with respect to Pleistocene climate change. These analyses indicate that E. farinosa displays patterns of genetic differentiation and geographic structuring consistent with postglacial range expansion. Populations of E. farinosa are characterized by distinct haplotype lineages significantly associated with geography. Centers of genetic diversity for the species occur in southwestern Arizona, the plains of Sonora, and Baja California Sur, all of which are putative sites of glacial refugia as predicted by analyses of macrofossil and pollen data. Nested clade analysis suggests that genetic structure in E. farinosa has been affected by past fragmentation followed by range expansion. Range expansion in several locations is further supported by significant departures from neutrality for values of Fu's F(S) and Tajima's D, and mismatch analyses.
更新世冰川作用对北半球植物物种的遗传结构产生了深远影响，原因在于分布范围的收缩、碎片化和扩张。系统地理学研究有助于我们了解这种影响在北美几个地理区域的情况，然而，很少有系统地理学研究考察索诺兰沙漠、莫哈韦沙漠和半岛沙漠中的植物物种。在本研究中，我们使用叶绿体DNA的psbA-trnH基因间隔区的序列数据，来获取关于分布范围内21个种群的310株粉苞菊（“脆叶菊”；菊科）个体间系统地理格局的信息。我们应用了多种种群和空间遗传分析方法，使我们能够依据更新世气候变化来解读数据。这些分析表明，粉苞菊呈现出与冰后期分布范围扩张相一致的遗传分化和地理结构模式。粉苞菊种群的特征是具有与地理显著相关的独特单倍型谱系。该物种的遗传多样性中心位于亚利桑那州西南部、索诺拉平原和南下加利福尼亚，所有这些都是根据大化石和花粉数据分析预测的冰川避难所假定地点。嵌套支系分析表明，粉苞菊的遗传结构受到过去碎片化随后分布范围扩张的影响。几个地点的分布范围扩张进一步得到了Fu氏F(S)和Tajima氏D值偏离中性以及失配分析的支持。
