Department of Ecology, Evolution and Behavior, University of Minnesota, Saint Paul, MN 55108, USA.
Mol Ecol. 2010 May;19(9):1877-97. doi: 10.1111/j.1365-294X.2010.04622.x. Epub 2010 Mar 30.
The integration of fossil and molecular data can provide a synthetic understanding of the ecological and evolutionary history of an organism. We analysed range-wide maternally inherited mitochondrial DNA and paternally inherited chloroplast DNA sequence data with coalescent simulations and traditional population genetic methods to test hypotheses of population divergence generated from the fossil record of Douglas-fir (Pseudotsuga menziesii), an ecologically and economically important western North American conifer. Specifically, we tested (i) the hypothesis that the Pliocene orogeny of the Cascades and Sierra Nevada caused the divergence of coastal and Rocky Mountain Douglas-fir varieties; and (ii) the hypothesis that multiple glacial refugia existed on the coast and in the Rocky Mountains. We found that Douglas-fir varieties diverged about 2.11 Ma (4.37 Ma-755 ka), which could be consistent with a Pliocene divergence. Rocky Mountain Douglas-fir probably resided in three or more glacial refugia. More variable molecular markers would be required to detect the two coastal refugia suggested in the fossil record. Comparison of mitochondrial DNA and chloroplast DNA variation revealed that gene flow via pollen linked populations isolated from seed exchange. Postglacial colonization of Canada from coastal and Rocky Mountain refugia near the ice margin at the Last Glacial Maximum produced a wide hybrid zone among varieties that formed almost exclusively by pollen exchange and chloroplast DNA introgression, not seed exchange. Postglacial migration rates were 50-165 m/year, insufficient to track projected 21st century warming in some regions. Although fossil and genetic data largely agree, each provides unique insights.
化石和分子数据的整合可以为生物体的生态和进化历史提供综合的理解。我们利用合并模拟和传统的种群遗传方法分析了广泛分布的母系线粒体 DNA 和父系叶绿体 DNA 序列数据，以检验从道格拉斯冷杉（Pseudotsuga menziesii）的化石记录中产生的种群分化假说，道格拉斯冷杉是一种生态和经济上重要的北美西部针叶树。具体来说，我们检验了以下假说：（i）喀斯喀特山脉和内华达山脉的上新世造山运动导致了沿海和落基山道格拉斯冷杉品种的分化；（ii）在沿海和落基山脉存在多个冰川避难所的假说。我们发现，道格拉斯冷杉品种大约在 211 万年前（437 万至 75.5 万年前）发生分化，这与上新世的分化时间一致。落基山道格拉斯冷杉可能存在于三个或更多的冰川避难所中。需要更多具有变异性的分子标记来检测化石记录中暗示的两个沿海避难所。线粒体 DNA 和叶绿体 DNA 变异的比较表明，通过花粉连接的种群的基因流与种子交换隔离。末次冰期最大冰川期时，沿海和落基山避难所的冰缘附近的加拿大的后冰川期殖民化产生了一个广泛的杂种带，这些杂种带几乎完全是由花粉交换和叶绿体 DNA 渐渗形成的，而不是由种子交换形成的。后冰川期的迁移率为 50-165 米/年，在某些地区不足以追踪到 21 世纪的预计变暖。尽管化石和遗传数据在很大程度上是一致的，但每一个都提供了独特的见解。
