Debruyne Régis
Muséum National d'Histoire Naturelle, Service de Systématique Moléculaire, FR 1541 CNRS, 43 rue Cuvier, F-75005 Paris, & UMR 5143 CNRS, Paléobiodiversité, 8 rue Buffon, F-75005 Paris, France.
Cladistics. 2005 Feb;21(1):31-50. doi: 10.1111/j.1096-0031.2004.00044.x.
Recent molecular phylogenies of the African elephants suggest that there is an evolutionary structure within Loxodonta africana. Some nuclear results (Roca et al., 2001) support the separation of the forest African elephant subspecies L. a. cyclotis as a species distinct from the savannah elephant L. a. africana, on the basis of the recognition of both forming highly divergent (reciprocally monophyletic) clades. Conversely, a mitochondrial survey (Eggert et al., 2002), while admitting a geographic partitioning of the genetic structure within African elephants, suggests retaining the status quo. They recognize three diagnosible entities (western, central and south-eastern Africa) with non-overlapping ranges within L. africana sensu lato. In order to address these conflicting views (historical fragmentation and speciation or isolation by distance, respectively), we have sequenced two datasets of 1961 bp (for 50 elephants) and about 3700 bp, respectively (for 20 elephants) of the mitochondrial DNA for both forms of elephants (cyclotis and africana). They span the cytochrome b gene, the control region and several RNAs. When compared with former mtDNA data, they provide the most comprehensive view of the African elephant phylogeny (78 mtDNA haplotypes, of which 44 are new) and provide the first insight into populations from the Democratic Republic of Congo. The genetic diversity of mtDNA was appraised and the stability of alternative phylogenetic trees was investigated. Our results are inconsistent with both those prior studies. They revealed two highly divergent molecular clades referred to as F and S, that do not conform to the morphological delineations of cyclotis and africana. A non-negligible proportion of specimens of L. a. africana display haplotypes prevailing in forest elephant populations (clade F). The geographic distribution of clades and areas of their co-occurrence support the hypothesis of incomplete isolation between forest and savannah African elephant populations, followed by recurrent interbreeding between the two forms. We state that the conclusions of prior studies resulted from insufficient character and/or geographic sampling. We conclude that there is no satisfying argument which can recognize two or more species of African elephants. We briefly comment on the meaning of such an attitude in a conservation viewpoint.
近期对非洲象的分子系统发育研究表明，非洲象（Loxodonta africana）内部存在一种进化结构。一些核基因研究结果（罗卡等人，2001年）支持将非洲森林象亚种L. a. cyclotis作为一个与非洲草原象L. a. africana不同的物种分离出来，这是基于二者形成高度分化（相互单系）分支的认识。相反，一项线粒体研究（埃格特等人，2002年）虽然承认非洲象内部存在遗传结构的地理划分，但建议维持现状。他们在广义的非洲象L. africana中识别出三个可诊断的实体（西非、中非和东南非），其分布范围不重叠。为了解决这些相互矛盾的观点（分别是历史上的片段化和物种形成或距离隔离），我们对两种非洲象（L. cyclotis和L. africana）的线粒体DNA进行了测序，分别获得了两个数据集，一个包含1961个碱基对（针对50头大象），另一个约为3700个碱基对（针对20头大象）。这些序列涵盖了细胞色素b基因、控制区和几个RNA。与之前的线粒体DNA数据相比，它们提供了关于非洲象系统发育的最全面视图（78个线粒体DNA单倍型，其中44个是新的），并首次深入了解了刚果民主共和国的象群。评估了线粒体DNA的遗传多样性，并研究了不同系统发育树的稳定性。我们的结果与之前的两项研究均不一致。结果显示存在两个高度分化的分子分支，分别称为F和S，这与L. cyclotis和L. africana的形态学划分不一致。相当比例的非洲草原象L. a. africana标本显示出森林象群中常见的单倍型（F分支）。分支的地理分布及其共存区域支持了非洲森林象和草原象种群之间未完全隔离，随后两种类型之间反复杂交的假说。我们指出，之前研究的结论是由于特征和/或地理采样不足导致的。我们得出结论，没有令人满意的论据能够将非洲象区分为两个或更多物种。我们从保护的角度简要评论了这种观点的意义。
