Department of Zoology, Faculty of Science, University of South Bohemia, 370 05 České Budějovice, Czech Republic.
Department of Zoology, Faculty of Science, University of South Bohemia, 370 05 České Budějovice, Czech Republic.
Mol Phylogenet Evol. 2018 Sep;126:105-115. doi: 10.1016/j.ympev.2018.04.003. Epub 2018 Apr 4.
Root-rats of the genus Tachyoryctes (Spalacidae) are subterranean herbivores occupying open humid habitats in the highlands of Eastern Africa. There is strong disagreement about species diversity of the genus, because some authors accept two species, while others more than ten. Species with relatively high surface activity, the giant root-rat Tachyoryctes macrocephalus, which is by far largest member of the genus, and the more fossorial African root-rat Tachyoryctes splendens, which eventually has been divided up to 12-13 species, represent two major morphological forms within the genus. In our study, we carried out a multilocus analysis of root-rats' genetic diversity based on samples from 41 localities representing most of Tachyoryctes geographic distribution. Using two mitochondrial and three nuclear genes, we found six main genetic clades possibly representing separate species. These clades were organised into three basal groups whose branching is not well resolved, probably due to fast radiation in the late Pliocene and early Pleistocene. Climatic changes in that time, i.e. fast and repeated changes between extremely dry and humid conditions, which both limited root-rat dispersal, probably stimulated their initial genetic diversification. Contrary to expectation based on the largest root-rat diversity in Kenya (up to eight species by some authors), we found the highest diversity in the Ethiopian highlands, because all but one putative species occur there. All individuals outside of Ethiopia belong to a single recently diverged and expanded clade. This species should bear the name T. annectens (Thomas, 1891), and all other names of taxa described from outside of Ethiopia should be considered its junior synonyms. However, to solve taxonomic issues, future detailed morphological analyses should be conducted on all main clades together with genetic analysis of material from areas of their supposed contact. One of the most interesting findings of the study is the internal position of T. macrocephalus in T. splendens sensu lato. This demonstrates the intriguing phenomenon of accelerated morphological evolution of rodents occupying the Afroalpine zone in Ethiopia. Finally, we discuss how the distribution of Tachyoryctes is influenced by competition with another group of subterranean herbivores on the continent, the African mole-rats. We assume that both groups do not compete directly as previously expected, but specialisation to different subterranean niches is the main factor responsible for their spatial segregation.
高山根田鼠（沙鼠科）是生活在东非高原开阔湿润生境中的穴居食草动物。关于该属的物种多样性存在很大分歧，因为一些作者只接受两个物种，而另一些作者则接受超过十个物种。相对来说，表面活动较高的物种，即迄今为止该属中最大的成员巨型高山根田鼠（Tachyoryctes macrocephalus），以及更穴居的非洲高山根田鼠（Tachyoryctes splendens），最终被分为 12-13 个物种，代表了该属内的两种主要形态形式。在我们的研究中，我们对来自代表高山根田鼠地理分布大部分地区的 41 个地点的样本进行了多基因座遗传多样性分析。利用两个线粒体和三个核基因，我们发现了六个主要的遗传分支，可能代表不同的物种。这些分支组成了三个基础组，它们的分支关系不太明确，可能是由于上新世晚期和更新世早期的快速辐射。当时的气候变化，即极度干燥和湿润条件之间快速而反复的变化，既限制了高山根田鼠的扩散，也可能刺激了它们最初的遗传多样化。与基于肯尼亚高山根田鼠最大多样性的预期相反（一些作者认为有多达 8 个物种），我们发现埃塞俄比亚高原的多样性最高，因为除了一个假定的物种外，其他所有物种都在那里。埃塞俄比亚以外的所有个体都属于一个最近分化和扩张的分支。这个物种应该被命名为 T. annectens（托马斯，1891 年），而所有其他在埃塞俄比亚以外描述的分类群的名称都应被视为其同物异名。然而，为了解决分类学问题，未来应该对所有主要分支进行详细的形态分析，并对假定接触区域的材料进行遗传分析。该研究最有趣的发现之一是巨型高山根田鼠在广义高山根田鼠 sensu lato 中的内部位置。这证明了埃塞俄比亚非阿勒皮地区啮齿动物形态进化加速的有趣现象。最后，我们讨论了高山根田鼠的分布如何受到与非洲地下食草动物鼹鼠科竞争的影响。我们假设这两个群体并不像以前预期的那样直接竞争，而是对不同的地下生态位的特化是导致它们空间隔离的主要因素。
