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Universidade do Porto (2017)

The role of inter-island gene-flow during colonization and speciation processes on archipelagos : analysis of the Micromeria Benth. (Lamiaceae) on the Canary Islands

Cardoso Curto Manuel António

Titre : The role of inter-island gene-flow during colonization and speciation processes on archipelagos : analysis of the Micromeria Benth. (Lamiaceae) on the Canary Islands

Auteur : Cardoso Curto Manuel António

Université de soutenance : Universidade do Porto

Grade : Doutoramento em Biodiversidade, Genética e Evolução 2017

Résumé partiel
Most of the diversity found in oceanic islands is produced by adaptive radiation events. This process is promoted by the high availability of free niches and isolation from the mainland typical for these systems. Hybrid swarms, where different lineages are combined through hybridization, are more likely to result in adaptive radiation events because new combinations of genotypes increase the adaptive ability of populations. Since the year 2000 several studies suggested that genetic diversity was higher than expected in the Canary Islands, which led to the creation of the surfing syngameon hypothesis. This hypothesis states that this pattern of high genetic diversity is a consequence of the creation of hybrid swarms after multiple colonization events of the archipelago. These populations diverge into species connected by gene-flow and evolve dependently from each other, also known as species syngameon. Although the surfing syngameon hypothesis was originally developed to explain the colonization of the entire archipelago, the same process might be applied to the colonization process of each individual island. In the present thesis I intend to test if this is the case by using the Micromeria species endemic to the Canary Islands as a system. Micromeria is distributed throughout all islands and ecological zones of the Canary Islands, and it has a high morphological variation. This genus contains groups of morphologically identical species, the most remarkable example being the species previously classified as M. varia s.l. Based on molecular phylogenetic analyses they show independent origins, and since they occupy similar habitats on different islands, a case of convergent evolution is indicated. Alternatively, in light of the reticulate patterns described on oceanic islands, these results can also be a consequence of introgression with other species from the same islands. In this situation, the detection of a single origin is prevented if only a few markers are used. In this thesis I focus on and compare the hypothesis regarding the extension of the surfing syngameon hypothesis to the colonization of each island and the possible single origin of the M. varia s.l. phenotype. The first hypothesis was tested by analyzing genetic structure, gene-flow, and diversity patterns in wider (entire archipelago) and local (Tenerife) scales, including all Micromeria species. To test the second hypothesis, a genomic dataset was used to evaluate the phylogenetic relationships of the species previously classified as M. varia. These objectives could only be addressed by developing new sets of molecular markers. Three marker sets were developed : exon primed and intron spanning sequencing markers (EPIC) ; microsatellites ; and RAD sequencing markers. The type of information they provide and the biases associated with different types of markers are discussed.

Mots clés  : Oceanic islands, Canary Islands, Micromeria, adaptive radiations, species syngameon, microsatellites, RAD-seq., introgression, hybridization, phylogeographic, phylogenomics, molecular markers.

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Page publiée le 7 décembre 2017