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Universidade do Porto (2015)

Evolutionary history of the Lesser Egyptian Jerboa, Jaculus jaculus, in Northern Africa using a multi-locus approach

Ana Filipa da Silva Moutinho

Titre : Evolutionary history of the Lesser Egyptian Jerboa, Jaculus jaculus, in Northern Africa using a multi-locus approach

Auteur : Ana Filipa da Silva Moutinho

Université de soutenance : Universidade do Porto

Grade : Mestrado em Biodiversidade, Genética e Evolução 2015

Résumé
Climate change and its effects on biodiversity is currently one of the most prominent scientific topics. The frequent shifts in climate caused significant changes in the Sahara-Sahel boundaries, leading to periodic modifications of the composition of habitats, thus influencing the distribution, ecology and evolution of the desert biota. Such dynamics resulted in new selective pressures and/or phylogeographic isolation of populations, causing events of genetic diversification, adaptation and eventually speciation. In this context, desert specialists such as African jerboas acquired the attention of researchers due to their broad geographic distribution across the SaharanArabian extent, and their great phenotypic and genetic polymorphism. Previous studies have recognized the existence of two divergent mitochondrial lineages within the Lesser Egyptian Jerboa (Jaculus jaculus), with a sympatric distribution in North West Africa. It has been proposed that the lineages could be reproductively isolated, forming two closely-related cryptic species. However, it was never evaluated if the reproductive isolation between clades indeed evolved, and if so, to what extent it had halted gene flow. In this respect, the present study aimed to verify the genome-wide signal of the differentiation between lineages, assess the evolutionary history of the species and estimate the potential processes driving speciation, thus highlighting the level of reproductive isolation between the putative species. By applying a comprehensive approach based on multiple independent loci and using population genetics, phylogenetic and phylogeographic methods, we validated the occurrence of two sympatric cryptic species within the Lesser Egyptian Jerboa. Both Structure and Isolation-with-Migration analyses showed very low frequency of gene flow between lineages, therefore suggesting strong, although not complete, reproductive isolation between species. The divergence level estimated is comparable to the one generally found between species, with the splitting age coinciding with the major climate shifts in North African regions during the Late Pliocene/Early Pleistocene boundary. The intralineages genetic variation suggested divergent demographic histories, where Lineage 1 experienced expansion slightly earlier than Lineage 2. Furthermore, the higher effective population size detected for Lineage 1 suggests an enhanced performance in occupying wider ranges when compared to Lineage 2, probably influenced by its competitive advantage over the micro-habitat preferences. According to the taxonomic norms, the two putative species could be named as J. jaculus and J. deserti, as has been previously proposed. We suggest that the process of speciation occurred in the presence of gene flow, wherein local adaptation probably had the key role in enhancing the recovered genetic diversity between species. However additional studies should be performed to further evaluate the possible geographic and ecological mechanisms behind the evolution and speciation in jerboas.

Mots clés  : cryptic species, demography, gene flow, local adaptation, natural selection, phylogenetics, population genetics, reproductive isolation, speciation

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