Ethiopian highlands as a cradle of the African fossorial root-rats (genus Tachyoryctes), the genetic evidence.

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.