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Universidade do Porto (2016)

Phylogeographic patterns in two North Saharan reptiles from the Western Maghreb

Joana Rodrigues Lopes dos Santos

Titre : Phylogeographic patterns in two North Saharan reptiles from the Western Maghreb

Auteur : Joana Rodrigues Lopes dos Santos

Université de soutenance : Universidade do Porto

Grade : Mestrado em Biodiversidade, Genética e Evolução 2016

Résumé
The Western Maghreb region is considered a hotspot of biodiversity and an important reservoir of endemism due to the heterogeneous climate and topography of this region and its complex geological history which have shaped the availability and distribution of numerous and varied habitats. Molecular assessments have successfully revealed a complexity of genetic lineages within many species, especially reptiles. However, the actual existing biodiversity is clearly underestimated due to large area cover by this region, the difficult access to remote areas and the political instability of many of these regions. In the Western Maghreb, the few studies available have focused on the northern regions of the Atlas Mountains. Therefore to contribute towards a better knowledge about diversity patterns of North Saharan species, this study involved a phylogeographic assessment, using a multilocus approach on two case studies. Ptyodactylus oudrii, the fan-footed gecko, inhabits the Eastern foothills of the Atlas Mountains and proximal arid regions from Morocco to Algeria. Previous preliminary studies detected considerable levels of genetic variability within this species, potentially indicating the presence of a cryptic species complex. In this work, we carried out a comprehensive phylogeographic screening, particularly in the possible contact zones between lineages, in order to determine the level of genetic variability and gene-flow within P.oudrii and to assess whether these lineages represent cryptic species. Maximum likelihood and Bayesian phylogenetic analyses based on two mitochondrial (12S and Cyt-b) and two nuclear (MC1R and RAG-2) markers showed four divergent genetic lineages with a strict association with geography. None of these lineages were found in sympatry and the level of haplotype sharing between them was minimal at all loci investigated. The orogeny of the Atlas Mountains took place at about the same time of the cladogenetic events between these lineages, thus suggesting a possible scenario of allopatric divergence mediated by the onset of a geographical barrier. An integrative approach will be necessary in order to assess the taxonomy of these lineages which should be treated distinct “species”, as according to molecular data. Uromastyx nigriventris, the spiny-tailed lizard, inhabits semi-deserts of sand, gravel and small rocks, in Morocco and Algeria. Previous works, focused on the Uromastyx genus, suggested only recently that U. nigriventris is a distinct species with low levels of intraspecific variation. We performed Maximum likelihood and Bayesian Inference phylogenetic analysis based on one mitochondrial gene (ND2) and two nuclear (RAG-1 and MC1R) markers to assess the genetic diversity and phylogeographic patterns of U. nigriventris. We found two divergent mitochondrial lineages with a clear association with geography : one in the northeastern and the other in the southwestern portions of the species’ range. The recent divergence of the lineages can be associated with the low variation of nuclear loci and the few instances of nuclear haplotype sharing between the two lineages suggesting a pattern of incomplete lineage sorting. Further research is needed to identify whether the lineages occur in sympatry or not. We speculated on a possible role of the Erg Chebbi formation as a long-term barrier between the two lineages in addition of the expansion of arid climate, during the Pleistocene and Pliocene climatic oscillations. Further studies are needed to confirm this hypothesis and to assess whether species co-distributed with U. nigriventris show similar phylogeographic patterns. Distinct processes associated with past climate and geologic events have been responsible for shaping the pattern of diversity, in the two studied Saharan species. Further research is required to understand the phylogeographic patterns and evolutionary processes shaping the distribution and genetic variation of species from the Western Maghreb, and in order to identify similar phylogeographic patterns and ecologic responses. Those findings will contribute to identify cryptic diversity, as well as priority target for conservation in terms of species and areas.

Mots Clés : Phylogeography ; Western Maghreb ; Biodiversity ; Atlas Mountains ; Pleistocene/Pliocene ; climatic oscillations ; Ptyodactylus oudrii ; Uromastyx nigriventris ;

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Page publiée le 1er janvier 2018, mise à jour le 23 août 2018