Phylogeography and evolutionary genetics of the weasel : (Mustela Nivalis)

Tese de doutoramento, Biologia (Biologia Evolutiva), Universidade de Lisboa, Faculdade de Ciências, 2015Understanding how the biogeography and evolutionary history of species affect their current distribution, genetic variation, phenotypic diversity and adaptation to different environmental conditions, is a major challenge in evolutionary biology. In this thesis, the least weasel (Mustela nivalis) was used as a model to study the impacts of the Pleistocene climatic oscillations on the contemporary patterns of genetic diversity across its European populations and to investigate footprints of divergent selection between regions with different climate and environment. The phylogeography and genetic structure of the least weasel in the Western Palearctic was investigated by identifying and inferring distinct lineages, glacial refugia, colonization routes and demographic history. The results suggested the existence of five glacial refugia (viz. Northeastern, Italian, southern Balkan, Carpathian and Anatolian) that contributed to the current extent and patterns of genetic variation and differentiation observed across Europe, and also of secondary contact zones where differentiated lineages meet. The origin and introduction history of the populations in the Mediterranean and Atlantic islands (Azores and São Tomé) was also studied. The results indicate that weasels were probably introduced in the Mediterranean islands during the last millennium BC, most likely to control commensal rodent populations. Weasels were introduced into Sicily and Corsica by Greek settlers and/or merchants from western Anatolia and into Malta, Sardinia and Balearic Islands by Phoenician settlers and/or traders. The origin of the Azorean weasels seems to be the Balearic Islands, brought by settlers or traders likely the fifteenth or early sixteenth centuries, while the population in São Tomé apparently descends of animals brought from the Azores with the Portuguese colonization in the sixteenth century. Mitochondrial DNA and microsatellite markers were used in the two above studies. The first genetic assessment, using mitochondrial DNA, of the origin and taxonomic status of the Egyptian weasel (M. subpalmata) was also carried out in this thesis. The results provide no evidence to support the view that the Egyptian weasel is genetically distinct from the least weasel and suggest that the colonization of North Africa is most likely a result from a natural expansion from the Middle East. Finally, a population genomic study was undertaken, with the main goal of searching for signatures of selection that may represent adaptations to different environmental conditions at two latitudinal extremes in Europe. Using the restriction-site-associated DNA sequencing technology (RADSeq), 4,896 single nucleotide polymorphisms (SNPs) were identified among weasel populations from Finland and Portugal. Candidate outlier loci were detected through genome scans of genetic differentiation and a total of one hundred and six SNPs exhibited outlier patterns and may have been targets of divergent selection. In conclusion, the results of this thesis contributed to improve our knowledge about the biogeographic history and evolutionary genetics of the least weasel and constitute a first step towards a wider use of this species as a mammalian model in genomic studies of adaptation to contrasting climates and environments