| Summary: | The adaptive potential of a species can be defined as its capacity to cope with environmental change. Adaptive potential increases with phenotypic variation, from the intra-individual to the inter-population level, but factors controlling and explaining this variation still remain poorly understood.We studied four plant species from Iles Kerguelen in the sub-Antarctic region which is currently facing one of the strongest climate changes worldwide. Plant species from Iles Kerguelen are known to show high phenotypic integration (i.e. strong correlation among traits), a phenomenon that has been suggested to constrain trait variation. For these species we studied what constrains phenotypic variation, considering the external environment, the internal phenotypic integration and the associated performance costs. We found that intra-individual variation, i.e. plasticity, may be constrained by complex environmental change and the performance costs it triggers. In contrast, plasticity may be favored by high degree of phenotypic integration (Chapter 3). We found that inter-individual variation within populations may not be constrained by environmental factors, but may be favored by high phenotypic integration (Chapter 1). We found inter-population variation within regions may be constrained by restricted environmental variation (Chapter 1). Finally, we studied secondary metabolites (amines and flavonols) that connect environmental variation to phenotypic variation. We found that compositions and functions of these metabolites vary among regions, probably reflecting evolutionary differentiation among regions (Chapter 2). Patterns of variation betweenregions suggest that within species metabolites may be functionally redundant or versatile, for which to our knowledge our results are the first hint. Overall, we suggest that climate change in Kerguelen will impact plant species performance, and that the persistence of suitable wet habitats will be determinant in species capacities to cope with such changes. Furthermore, this ...
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