The Sahara as a vicariant agent, and the role of Miocene climatic events, in the diversification of the mammalian order Macroscelidea (elephant shrews)

Abstract

Although the Sahara is a major geographical feature of the African continent, its role in the diversification of animal species is not well understood. We present here a molecular phylogeny for members of the endemic African mammalian order Macroscelidea (elephant shrews) with molecular-clock calculations; this molecular phylogeny provides convincing evidence that the genus Elephantulus is diphyletic. Elephantulus rozeti, the only elephant shrew species that resides north of the Sahara, is the sister group of a species from a different genus (Petrodromus tetradactylus), which resides just south of the Sahara. The split between these taxa coincided with major Miocene climatic events, which triggered the cooling and aridification of midlatitude continental regions, and a shift in the Sahara from a tropical to an arid environment. Thus, the North African distribution of E. rozeti is not the result of dispersion from an eastern species of the genus, but instead the result of a vicariant event involving the formation of the Sahara. The splitting events involved with most Elephantulus species in our analysis appear to coincide with these climatic events. This coincidence suggests that the environmental consequences associated with this period played an important role in the radiation of this order of mammals. The strongly supported phylogeny provides compelling evidence for a complex history of mosaic evolution, including pronounced bradytelic morphological evolution in some lineages, accelerated morphological evolution in others, and a remarkably slow rate of evolution of the male reproductive structure.

Reconstructing the tempo and mode of evolution in an extinct clade of birds with ancient DNA: The giant moas of New Zealand

“…As in most North American birds (36,37), moa speciation events occurred during the phase of rapid cooling before the Pleistocene, whereas phylogeographic subdivisions within species developed 1-2 mya after the onset of the Pleistocene Ϸ2.5 mya (38). Paleoenvironmental changes have therefore had a profound influence on the tempo and mode of evolution in moa, adding to the growing body of evidence that the evolutionary history of vertebrates has been shaped by many of the same large-scale environmental events (39)(40)(41)(42)(43).…”

Spatial genetic structure in the Laperrine's olive (Olea europaea subsp. laperrinei), a long-living tree from the central Saharan mountains

“…Since the upper Miocene, it represents a natural barrier between Mediterranean and Tropical Africa which is difficult to cross for living organisms (Douady et al, 2003). The number of species present in this area is particularly limited (Quézel, 1965), but the ratio of endemic species is relatively high in mountains that act as refugia for plants and animals due to higher rainfall in altitude.…”

Ancient watercourses and biogeography of the Sahara explain the peopling of the desert

“…For example, genetics indicates that the Sahara has been a barrier to the dispersal of Macroscelidea (elephant shrews) since the late Miocene when the desert first formed (6), whereas pollen analysis of terrestrial sediments from the central Sahara demonstrates that during the Holocene humid period an arid belt existed north of 22° (7). Furthermore, arid plant taxa are found continuously through Atlantic Ocean cores between 23°and 27°north for the last 250 ka suggesting a longlasting Saharan arid belt at this latitude (8).…”