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Theses

Phenotypic and genetic characterisation of the carabid beetle Merizodus soledadinus along its invasion gradient at the subantartic Kerguelen Islands

Abstract : Global trade and human movements increase the likelihood of long-distance transportation of propagules and their subsequent introduction into new geographic regions. In some instances, newly established species can become dominant in invaded communities, at the expense of native species. Besides threatening invaded communities and ecosystem functions, biological invasions constitute natural experiments that allow to study eco-evolutionary processes in real time, including the occurrence of new biotic interactions affecting community composition, rapid adaptation to novel environmental conditions, or dispersal evolution at range margins. Because of their impoverished native communities, oceanic islands’ ecosystems are particularly sensitive to biological invasions, and the French subantarctic islands are no exception. For instance, the flightless predatory carabid beetle Merizodus soledadinus is native from the southern tip of South America, and has been accidentally introduced to the Kerguelen Islands in 1913. In the present work, we aimed at understanding the main mechanisms underlying the invasive success of this insect at the Kerguelen Islands. Using a vast array of methodologies, ecological features of M. soledadinus were investigated with analytical procedures scaling from population to molecule through the individual level. Genetic investigations support the historically-based hypothesis of a single introduction event at a unique location of the Kerguelen Islands. No genetic structure was observed among individuals sampled from different populations along the invasion gradient. We tested the hypothesis of spatial sorting of populations during range expansion, by exploring phenotypic changes among individuals sampled along the invasion gradient. The measured phenotypic traits revealed major differentiation of adults according to the residence time of their populations, confirming the occurrence of spatial sorting of populations during geographic expansion. We also demonstrated that the geographic expansion of M. soledadinus, and microhabitat selection, are primarily governed by the availability of water resources, as suggested by the high sensitivity to water stress of adults of this ground beetle. In parallel, colonisation of altitudinal habitats is governed by thermal conditions, which seem to be physiologically constraining from 200m asl onwards. As the altitudinal distribution of M. soledadinus still extends, we concluded that ongoing climatic changes play a pivotal role in this expansion. Finally, adults of this ground beetle are long-lived and active year-round. The ecological knowledge of M. soledadinus characteristics and spatial expansion dynamics suggest that the colonisation process of the Kerguelen archipelago by this species will continue. Altogether, these data could be used for parametrising range expansion models that would delineate dispersal pathways and expansion rates, in the objective to assist stakeholders’ management decisions.
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Tiphaine Ouisse. Phenotypic and genetic characterisation of the carabid beetle Merizodus soledadinus along its invasion gradient at the subantartic Kerguelen Islands. Biodiversity and Ecology. Université Rennes 1, 2016. English. ⟨NNT : 2016REN1B017⟩. ⟨tel-01494619⟩

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