In my research projects, I study the evolutionary processes that govern the adaptation of populations to new environments and shape the evolutionary dynamics of these populations. On the one hand, I aim to understand the factors and mechanisms that promote adaptation and influence the adaptive ability of the organism. On the other hand, and in a complementary way, I am also interested in understanding the factors that limit and constrain adaptation.
Evolutionary rescue to understand limits of adaptation
Due to climate change and human disturbance, environmental changes are becoming more rapid and frequent. Populations undergoing these challenging environments, will adapt or decline and risk eventually going extinct. The process by which a population adapts to this stress, reducing the risk of extinction, is called ‘evolutionary rescue’. Many factors, as the genetic diversity of populations, the duration of stress to which individuals are exposed, the negative density dependence, etc. can impact the probability that a population will rescue or not. The influence of these factors and their interaction has already been demonstrated theoretically or with elegant experiments using yeast, algae and bacteria and populations harboring substantial standing genetic variation. Nevertheless, in diploid sexual species with small populations, the conditions that permit evolutionary rescue are likely to be more stringent and are less understood. Therefore, I am using the flour beetle Tribolium castaneum to perform evolutionary rescue experiments in an attempt to understand the factors influencing and limiting adaptation.
Local adaptation to host plant: from experimental populations to natural populations
Local adaptation corresponds to the dynamic process of increased matching of phenotypic features of an organism to its local environmental conditions. While this process is widespread, the evolutionary forces and ecological factors influencing its dynamics remains unclear. To further our understanding of the local adaptation process, I conducted experiments in the laboratory and in the field. Using the model organism Drosophila suzukii, a generalist crop pest, I focused on adaptation to the host plant
Using experimental evolution, many local adaptation studies have shown that populations evolving in one environment experience an increase in fitness in both their own selective environment and in an alternative contrasted environment. Using adaptive landscape theory, we can understand these surprising results. During adaptation, the increase in fitness in one environment of a population initially maladapted is associated with an increase and then a decrease in fitness in the other environment. To test these predictions, I performed an experimental evolution where populations of D. suzukii evolved in three different fruits. Using reciprocal transplant experiments at different time steps, we measured how fitness correlations between environments change over time. This project illustrates how temporal study of fitness changes in selective and alternative environments across multiple generations allows a better characterization of the dynamics of local adaptation compared to typical cross-sectional studies performed over a single generation.
Because of the multitude of interacting factors, the evolution of local adaptation in the field remains more difficult to track. While coarse-grained environments are expected to promote local adaptation, fine-grained environments are expected to promote adaptive phenotypic plasticity. However, when heterogeneity is intermediate, it remains unclear the extent to which these effects contribute to maintain the match between phenotype and local environment. We sampled natural populations of D. suzukii on different fruits to perform a reciprocal transplant experiment over multiple generations in the laboratory. We developed a new statistical method and estimate the relative contributions of adaptive phenotypic plasticity and local adaptation in these patterns. We show that rapid evolution of local adaptation to host fruits. This study demonstrates that spatially and temporally variable selection can maintain genetic and phenotypic variation and that local adaptation can evolve rapidly in natural populations.
Genomic basis of adaptation and evolutionary changes during a biological invasion
Within their introduced range, populations of invasive species are likely to have successfully adapted, over a short period of time, to a wide range of biotic and abiotic conditions that they might not have experienced in their region of origin. They thus represent attractive evolutionary situations for characterizing the genomic basis of adaptation to new environments, a major challenge in modern evolutionary biology. To identify genomic selection signals associated with the invasion of Drosophila suzukii, we used the sequences of population-specific pools of individual DNA (Pool-Seq) representative of the current worldwide genetic diversity of the species in both its native and invasive ranges. Using recent methodology developed by Mathieu Gautier and implemented in the computer program BayPass, we conducted association analyses with the invasive versus native status of the genotyped populations and with bioclimatic variables corresponding to the geographical locations of the populations. Capitalizing on the detailed genomic resources available in Drosophila melanogaster, its sister species, we will further perform a detailed annotation of the associated variants to identify physiological pathways involved during the invasive process.