Abstract
BackgroundThe Ethiopian highlands are a biodiversity hotspot, split by the Great Rift Valley into two distinct systems of plateaus and mountains. The Rift Valley is currently hot and dry and acts as a barrier to gene flow for highland-adapted species. It is however unlikely that the conditions in the Rift were inhospitable to highland species during the entire Pleistocene. To assess the significance of the Ethiopian Rift as a biogeographic barrier as well as the impact Pleistocene climatic changes have had on the evolution of Ethiopian organisms, we performed phylogeographic analyses and developed present and past niche models on seven anuran species with different elevational and ecological preferences.ResultsWe found that highland species on the east and the west sides of the Rift are genetically differentiated and have not experienced any detectable gene flow for at least 0.4 my. In contrast, species found at elevations lower than 2500 m do not show any population structure. We also determined that highland species have lower effective population sizes than lowland species, which have experienced a large, yet gradual, demographic expansion, starting approximately half a million year ago.ConclusionsThe pattern we report here is consistent with the increasingly warmer and drier conditions of the Pleistocene in East Africa, which resulted in the expansion of savanna, the fragmentation of forests and the shrinking of highland habitats. Climatic niche models indicated that the Rift is currently non suitable for most of the studied species, but it could have been a more permeable barrier during the Last Glacial Maximum. However, considering the strong genetic structure of highland species, we hypothesize that the barrier mechanisms at the Rift are not only climatic but also topographical.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0774-1) contains supplementary material, which is available to authorized users.
Highlights
The Ethiopian highlands are a biodiversity hotspot, split by the Great Rift Valley into two distinct systems of plateaus and mountains
Ptychadena cooperi was always found near water, usually large ponds and slow running streams and rarely in flooded grasslands and never in the large streams favored by Amietia sp
We reconstructed the evolutionary history of seven frog species with different elevational and ecological preferences and we examined the impact the Great Rift Valley (GRV) has had on their population structure
Summary
The Ethiopian highlands are a biodiversity hotspot, split by the Great Rift Valley into two distinct systems of plateaus and mountains. The Ethiopian highlands constitute the largest continuous mountain system in Africa These highlands are a biodiversity hotspot [1], for amphibians as ~40 % of the species found in the highlands are endemic [2, 3]. The Ethiopian highlands are split by the Great Rift Valley (GRV) in two systems of plateaus and mountains: the Western highlands (or Abyssinian massif ) and the Eastern highlands (or Harar massif ). During drier periods the GRV could have acted as a barrier to dispersal for highland-adapted species as their distribution was being pushed to higher elevations. When the climate was wetter, highland species could have expanded their distribution toward low elevations and could have eventually dispersed across the GRV
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