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ETH ZURICH (2013)

Low impact of altitude and landscape composition on patterns of genetic variation in semi-dry grassland plants

Hahn Thomas

Titre : Low impact of altitude and landscape composition on patterns of genetic variation in semi-dry grassland plants

Auteur : Hahn Thomas

Etablissement de soutenance : ETH ZURICH

Grade : Doctor of Sciences 2013

Résumé partiel
Climate change is among the most serious threats for global biodiversity. Many mountain regions experience particularly strong climatic changes while mountain plants are expected to be especially sensitive to such changes. Potential reactions of plants to the changing environmental conditions are plastic responses, genetic adaptation or migration to locations where environmental conditions are becoming suitable, the ultimate alternative being local extinction. The upwards migration potential for plants in mountain areas is determined by several factors. For plant populations in the current upper range periphery, population fitness and particularly seed production are important prerequisites to successfully establish new populations at higher altitudes. In predominantly outbreeding plants, fitness of populations is often linked to genetic diversity and inbreeding. For clonal plants, a high investment in vegetative reproduction can reduce sexual reproduction. In the semi-dry grassland species, Briza media, Trifolium montanum and Ranunculus bulbosus, I investigated the effect of altitude on neutral genetic diversity, genetic differentiation, levels of inbreeding as well as the importance of clonal reproduction, using AFLP fingerprints. I studied the impact of landscape composition on historic gene flow among populations. This PhD project is part of the CCESBioChange project and is strongly linked to the PhD projects of Esther Frei and Philippe Matter. In the first study, I tested whether in the three model species upper peripheral plant populations in mountainous areas are smaller, genetically depleted, genetically more differentiated and more inbred compared to populations at lower altitudes. Estimations of size, isolation and genetic diversity of populations were not affected by altitude and only in B. media inbreeding was greater at higher altitudes. Genetic differentiation was slightly greater among populations at higher altitudes in B. media and individuals within populations were more related to each other compared to individuals in lower altitude populations. A similar but less strong pattern of differentiation and relatedness was observed in T. montanum, while in R. bulbosus no effect of altitude was apparent. Because populations in the upper periphery were not genetically depauperate or isolated, they may be important source populations for migration under climate change. In the second study, I assessed how altitude, landscape elements and individual density affect genetic differentiation in T. montanum within two valleys in South-Eastern Switzerland (Canton Grisons). Forest area had in both valleys no effect on historical gene flow at the landscape scale. Within one valley, area of semi-dry grassland, road area and altitude slightly 5 influenced genetic differentiation among sampling sites, suggesting regional variation in effects. These patterns of genetic differentiation suggests that a future increase in forest area, due to land use abandonment, at least in the short term is unlikely to directly impact on patterns of genetic diversity in T. montanum.

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