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Evolution et adaptation des Espeletiinae dans les Andes tropicales

Abstract : The high-elevations ecosystems in the Northern Andes, known as paramos, exhibit an exceptional diversity of species accounting for 10 to 20% of Andean flora's richness and contain the fastest alpine plant radiation in the world. The Espeletiinae (Asteraceae, Heliantheae), endemic to these habitats and among these major examples of Andean diversification, took advantage of the ecological benefits provided by the uplift of the páramos, by developing a remarkable morphological and ecological diversity in less than 3 Ma to cope with the abiotic stresses of these ecosystems. This complex of +/- 135 species includes branched tree life forms, dwarf rosettes, and caulescent as well sessile as giant rosettes, constituting an emblematic adaptation of tropical alpine environments. These plants are also diversified in páramo, in wetlands, open alpine meadows or rocky slopes from the upper limit of the Andean forests at 2500m altitude to the edges of the glaciers at 4600m. Such morphological and ecological diversity, in association with high sympatric rates between these species, led to the hypothesis of an adaptive radiation of Espeletiinae. However, the first phylogenetic reconstructions, testing this evolutionary origin, failed to depict any relationships between these species because of the very recent evolution of the complex, the use of traditional phylogenetic markers and/or the widely hybridization events, which could skew the phylogenetic signal. Today, the advent of new sequencing technologies offers new perspectives in phylogenomics. As a result of this thesis work, the use of random (shotgun-sequencing) and targeted genomic fragments (by ddRAD-sequencing method) made it possible to reconstruct for the first time robust phylogenies and to study the hybridization events inside this complex, bringing new answers to the evolution of these plants in the páramos.
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Charles Pouchon. Evolution et adaptation des Espeletiinae dans les Andes tropicales. Biodiversité et Ecologie. Université Grenoble Alpes, 2018. Français. ⟨NNT : 2018GREAV018⟩. ⟨tel-01989094⟩

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