Abstract
The distribution range of a species corresponds to the geographical expression of its ecological niche, i.e. the set of biotic and abiotic conditions that allow the survival and reproduction of individuals. Thus, the genetic and phenotypic variability of a species is associated with the diversity of environments in which the species evolves. Among others, competition between plants, water stress or disturbances (i.e. partial or total destruction of biomass) represent major selection pressures for plants. However, adaptation within the range to these different environments is constrained by several evolutionary and ecological processes, particularly in relation to colonization history. In functional ecology, adaptation to different environments has been addressed by describing the diversity of functional traits based on interspecific comparisons. The study of trait relationships along environmental gradients has allowed the description of ecological strategies in plants at the interspecific scale, supposed to represent the adaptive response of populations to these environments. However, the adaptive nature of these ecological strategies remains to be determined and requires further study at the intraspecific scale to better understand the relationships between traits, performance and environments. Thus, studying the variability, distribution and evolution of the ecological strategies of a species within its distribution allows to question the local adaptation of the species in different environments, and to confront the expectations of functional ecology at the intraspecific scale. In this context, we used of the model species Arabidopsis thaliana, for which sequencing data allow a better understanding of the evolutionary mechanisms at the origin of phenotypic diversity. Its short life cycle and small size also make it an excellent model to study in controlled environments. Thanks to sequencing data, the demographic history of the species has recently been described and thus allows a better understanding of the geographical structure of phenotypic diversity and the evolution of the different ecological strategies that coexist within this species. Through a series of experiments, we have shown that the colonization of A. thaliana in northern Europe was concomitant with an adaptation to water stress, in trade-off with the reproductive capacity. Consequently, adaptation to water stress in northern Europe is one of the factors that determine the latitudinal limits of the range of this species. We also showed that the maintenance of the relict populations in the Iberian Peninsula was associated with a better tolerance to competition compared to the modern populations, which recolonized Europe from the Balkans 10,000 years ago. This tolerance to competition, associated with a higher seed mass, is in trade-off with the dispersal capacity, selected in return in these modern populations. Recent evolution of A. thaliana within its range is associated with adaptation to different land use, from forests to urban or agricultural environments. Populations in urban and agricultural environments show trait values associated with greater tolerance to disturbance, whereas populations in non-artificial environments show trait values associated with stress tolerance. Land use, in interaction with climate, is thus a major, yet still neglected, factor in the phenotypic and genotypic divergence of the species in Europe. Overall, this work allowed us to understand the evolution of the different ecological strategies during the colonization of the current distribution area of A. thaliana. These strategies are the result of major evolutionary trade-offs between stress survival, dispersal ability, competition tolerance and disturbance avoidance. An interdisciplinary approach, at the crossroads of functional ecology, biogeography and evolutionary biology, has led to a better understanding of the ecological and evolutionary determinants of a species' range