Roca Alfred L, Georgiadis Nicholas, O'Brien Stephen J
Laboratory of Genomic Diversity, Basic Research Program, SAIC-Frederick, Frederick, MD 21702, USA.
Quat Int. 2007 Jul;169-170:4-16. doi: 10.1016/j.quaint.2006.08.008.
Studies of skull morphology and of nuclear DNA have strongly concluded that African elephants comprise two species. Nonetheless, Debruyne (2005) has suggested a single-species model for Loxodonta based on the polyphyly of a single genetic locus, mitochondrial DNA (mtDNA). Discordant patterns between mitochondrial and nuclear DNA markers were subsequently reported in some African savanna elephant populations, further supporting a two-species model, and prompting us to re-examine here the geographic distribution of different elephant morphotypes and their relationship to nuclear and mtDNA phylogeographic patterns. We used exact tests to compare the distribution of forest elephant-typical and savanna elephant-typical characteristics across eight published datasets containing morphological, mtDNA or nuclear DNA data for African elephants. Among the elephants examined by Debruyne (2005), we found that patterns of forest vs. savanna characteristics were significantly different (p < 10(-5)) between mtDNA and morphology, suggesting the presence of cyto-nuclear genomic dissociation. We show that the eight African elephant continent-wide datasets compared, including that of Debruyne (2005), together support a two-species model with cyto-nuclear genomic dissociation rather than a one-species model, and together indicate that Africa harbors two species of elephant.
对头骨形态和核DNA的研究已有力地得出结论，非洲象包含两个物种。尽管如此，德布鲁因（2005年）基于单个基因位点——线粒体DNA（mtDNA）的多系性，提出了一个关于非洲象属的单物种模型。随后，在一些非洲草原象种群中报告了线粒体和核DNA标记之间的不一致模式，进一步支持了双物种模型，并促使我们在此重新审视不同大象形态类型的地理分布及其与核DNA和线粒体DNA系统发育地理模式的关系。我们使用精确检验来比较在八个已发表的数据集中森林象典型特征和草原象典型特征的分布情况，这些数据集包含非洲象的形态学、线粒体DNA或核DNA数据。在德布鲁因（2005年）研究的大象中，我们发现线粒体DNA和形态学之间森林与草原特征的模式存在显著差异（p < 10^(-5)），这表明存在细胞核基因组解离。我们表明，所比较的八个全非洲象数据集，包括德布鲁因（2005年）的数据集，共同支持一个具有细胞核基因组解离的双物种模型，而不是单物种模型，并且共同表明非洲有两种大象。
