Comparative Phylogeography of Ethiopian anurans: impact of the Great Rift Valley and Pleistocene climate change

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.

Diversification of African tree frogs (genus Leptopelis) in the highlands of Ethiopia

“…The GRV has shaped the genetic structure of a multitude of plants and animals. These include the frog genera Amietia, Ptychadena and Xenopus (Evans et al., ; Freilich et al., ; Manthey et al., ), mammals, for example, the Gelada baboon and the Ethiopian wolf (Belay & Mori, ; Gottelli et al., ), as well as plants (Kebede et al., ; Silvestrini et al., ). The split between populations on either side of the GRV appears to be older in Leptopelis (~4–6 mya) than in other genera of frogs such as Amietia (0.4 mya), Ptychadena (0.4–0.5 mya) and Xenopus (~1–3.5 mya).…”

“…Studies of other frog species that inhabit the Arsi plateau revealed no evidence of population structure within the plateau, for example, within Amietia nutti (Freilich et al., ; Manthey et al., ), Xenopus clivii (Evans et al., ), Ptychadena cooperi and P. cf . neumanni 2 (Freilich et al., , ; Reyes‐Velasco et al., ). Ptychadena cf.…”

“…The amphibian fauna of the region is of special interest, as it contains five endemic genera (four anurans and one caecilian), while about half of all amphibian species in the country are endemic (Largen & Spawls, ; Mengistu, Nagel, Getahun, Saber, & Loader, ). Many of the endemic taxa of these highlands have affinities to lowland species from other regions of Africa (Freilich, Tollis, & Boissinot, ; Freilich et al., ; Loader et al., ; Siu‐Ting et al., ), while several species that are lowland generalists elsewhere have adapted to high elevations in the Ethiopian highlands (Largen & Spawls, ).…”

“…The Great Rift Valley (GRV) crosses the highlands from NE to SW, dividing them into two main blocks, which are the Abyssinian massif to the north, and the Harar massif to the south (see Figure ). The GRV is known to be an important barrier to the dispersal of a multitude of taxa (Evanno, Regnaut, & Goudet, ; Freilich et al., ; Gottelli, Marino, Sillero‐Zubiri, & Funk, ; Kebede, Ehrich, Taberlet, Nemomissa, & Brochmann, ; Manthey, Reyes‐Velasco, Freilich, & Boissinot, ; Reyes‐Velasco, Manthey, Bourgeois, Freilich, & Boissinot, ; Smith, Noonan, & Colston, ). Other hydrological features also played an important role in the complex geology of the region and in the diversification of Ethiopian taxa, in particular the Omo River Valley and the Blue Nile Valley (Evans, Bliss, Mendel, & Tinsley, ; Freilich et al., ; Gottelli et al., ; Manthey et al., ; Reyes‐Velasco et al., ).…”

Integrating life history traits into predictive phylogeography

“…Although many current comparative phylogeographic data sets are taxonomically restricted, for example to a regional avifauna (e.g., Kirchman & Franklin, 2007), or to regional anurans (e.g., Freilich et al, 2016), cross kingdom studies (e.g., Carstens, Brunsfeld, Demboski, Good, & Sullivan, 2005;Hewitt, 1996;Sérsic et al, 2011) and syntheses (e.g., Médail & Diadema, 2009;Soltis, Morris, McLachlan, Manos, & Soltis, 2006) are beginning to accumulate. The broad taxonomic sampling of such studies leads to inherent difficulties related to the comparison of genetic variation, but model selection and species-specific simulations represent powerful tools to test ecosystem-wide hypotheses (e.g., Carstens et al, 2005;Carstens & Richards, 2007) and make species-specific predictions (e.g., Ruffley et al, 2018;Smith, Ruffley, Tank, Sullivan, & Carstens, 2017), enabling such cross-kingdom comparisons.…”