Spinks Phillip Q, Shaffer H Bradley
Section of Evolution and Ecology, University of California, Davis, California 95616, USA.
Mol Ecol. 2005 Jun;14(7):2047-64. doi: 10.1111/j.1365-294X.2005.02564.x.
We analysed phylogeography and population genetic variation across the range of the western pond turtle (Emys marmorata) using rapidly evolving mitochondrial and nuclear DNA sequence data. Nuclear DNA sequences from two unlinked introns displayed extremely low levels of variation, but phylogenetic analyses based on mtDNA recovered four well-supported and geographically coherent clades. These included a large Northern clade composed of populations from Washington south to San Luis Obispo County, California, west of the Coast Ranges; a San Joaquin Valley clade from the southern Great Central Valley; a geographically restricted Santa Barbara clade from a limited region in Santa Barbara and Ventura counties; and a Southern clade that occurs south of the Tehachapi Mountains and west of the Transverse Range south to Baja California, Mexico. An analysis of molecular variance (amova) based on regional hydrographic units revealed that populations from the Sacramento Valley north to Washington were virtually invariant, with no evidence of population substructure among northern river drainage basins. In other areas, E. marmorata contains considerable unrecognized variation, particularly in central and southern California and in northern Baja California, Mexico. Our northern clade is congruent with the distribution of the subspecies Emys marmorata marmorata (Washington-central California). However, no clade is congruent with the distribution of the southern subspecies Emys marmorata pallida from central California-Baja. Thus, recognition of the current subspecies split is not warranted, based on the available genetic evidence. Our amova and phylogenetic results, in conjunction with a growing comparative database for other codistributed aquatic taxa, confirm the occurrence of genetic breaks across the Tehachapi Mountains and Transverse Range bounding the southern end of the Great Central Valley, and point to southern California as a rich source of cryptic genetic variation.
我们利用快速进化的线粒体和核DNA序列数据，分析了西部锦龟（Emys marmorata）分布范围内的系统地理学和种群遗传变异。来自两个不连锁内含子的核DNA序列显示出极低的变异水平，但基于线粒体DNA的系统发育分析恢复了四个得到充分支持且地理上连贯的分支。其中包括一个大型的北方分支，由从华盛顿州南部到加利福尼亚州圣路易斯奥比斯波县、海岸山脉以西的种群组成；一个来自中央大谷地南部的圣华金谷分支；一个地理范围受限的圣巴巴拉分支，来自圣巴巴拉县和文图拉县的有限区域；以及一个南方分支，分布在 Tehachapi 山脉以南和横向山脉以西，一直延伸到墨西哥下加利福尼亚州。基于区域水文单元的分子方差分析（AMOVA）显示，从萨克拉门托谷到华盛顿州的种群几乎没有变异，北部河流流域之间没有种群亚结构的证据。在其他地区，西部锦龟包含大量未被认识到的变异, 特别是在加利福尼亚州中部和南部以及墨西哥下加利福尼亚州北部。我们的北方分支与亚种Emys marmorata marmorata（华盛顿州 - 加利福尼亚州中部）的分布一致。然而，没有一个分支与来自加利福尼亚州中部 - 下加利福尼亚州的南方亚种Emys marmorata pallida的分布一致。因此，根据现有的遗传证据，目前对亚种划分的认可并不合理。我们的AMOVA和系统发育结果，结合其他同域分布水生类群不断增长的比较数据库，证实了在界定中央大谷地南端的Tehachapi山脉和横向山脉存在遗传间断，并指出南加利福尼亚是隐性遗传变异的丰富来源。
