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Etude des processus de spéciation associés à une zone de transition biogéographique : exemple de l'algue brune Lessonia nigrescens

Abstract : Understanding the mechanisms that limit the natural range of species distribution is a major challenge in biodiversity, because it falls within the descripti on of global change and the analysis of its evoluti on. Using a combination of both ecological and genetic approaches, this thesis aimed to understand the mechanisms responsible for the origin of the distribution of genetic diversity, and those that contribute to their maintenance in the brown algae Lessonia nigrescens. This large brown alga (kelp) forms veritable forests and dominates the intertidal rocky shore along the Chilean coast. The first objective of this thesis was to study the phylogeography of this species, and compared it with that of the phylogenetically closest species, Lessonia trabeculata, which is present at the subtidal level. Through an approach that used markers from each of the genomic compartment, it has been revealed a concordance between the biogeographic transition zone described at 30°S and a major discontinuity in L. nigrescens, whereas L. trabeculata did not show such any genetic structuring. The combination of the phylogeographic approach with population genetics have shown that the two lineages described in L. nigrescens constitute cryptic species, reproductively isolated and, although have overlapping distributio n ranges, they are never observed in sympatry. In order to better understand the processes acting in the contact zone, reciprocal transplants and response to temperature experiments were made. The results show that the distribution of these cryptic species along the Chilean coast is undoubtedly under the effect of some environmental factors. However, the absence of sympatry at a local scale cannot be explained without including mechanisms linked to reproductive isolation and/or a competitive interaction between both species. Moreover, the presence of cryptic species having distinct ecological niches has a direct consequence on the management of the natural resource. Particularly, the species distributed northern of the 30°S (PP species) seems to have a high risk of extinction, because of the important anthropic and natural perturbations at which it is exposed.
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Submitted on : Monday, April 29, 2013 - 10:58:56 AM
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  • HAL Id : tel-00814626, version 1

Citation

Florence Tellier. Etude des processus de spéciation associés à une zone de transition biogéographique : exemple de l'algue brune Lessonia nigrescens. Biodiversité. Université Pierre et Marie Curie - Paris VI, 2009. Français. ⟨NNT : 2009PA066765⟩. ⟨tel-00814626⟩

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