The genetics of adaptation at a species’ southern range edge

This study investigates the factors influencing the geographic distribution and adaptive potential of Arabidopsis lyrata subsp. lyrata, a plant species with a restricted distribution in Northern America. The research addresses questions posed by ecologists and evolutionary biologists regarding the limitations of species adaptation and the drivers of geographic distribution. The study integrates ecological and evolutionary perspectives. On the one hand, by exploring the interplay of ecological constraints resulting from steep environmental gradients. On the other hand, evolutionary challenges of genetic drift, reduced genetic diversity, and trade-offs between adaptive traits. The focus is on the southern range edge, where climate change is expected to impose rapid and frequent environmental shifts.
Chapter I investigates how genetic diversity is maintained in a dynamic dune landscape, revealing signs of local adaptation through a genome-wide association study. The analyses identify outlier genes associated with reproductive development, highlighting the role of landscape features and climate in driving genetic differentiation.
Chapter II explores genetic constraints on traits of adaptation using a greenhouse stress experiment that simulates climatic conditions at the southern range edge. While phenotypic performance differences suggest synergistic effects under multi-stress conditions, genetic variance-covariance matrices reveal complex patterns with potential limitations to multivariate genetic variation. Constraints between growth traits and their divergence from selection pressure emphasize the challenges of adapting to changing environmental conditions.
Chapter III examines the genomic basis of the differences in performance using a natural selection experiment along the southern range edge in the USA. Family effects within the greenhouse experiment explain a high fraction of the observed variance, emphasizing the complexity of natural environments. Gene-level analysis reveals low overlap between treatment and common garden sites for the same trait, highlighting the intricate genetic pathways involved in trait establishment.
In conclusion, the study highlights the complexity of genetic processes shaping adaptive potential. While genetic variability is present under range edge conditions, the multi-environmental nature introduces genetic constraints. The study underscores the importance of considering landscape context and genetic complexities in understanding a species' adaptive responses to environmental changes. The speed of adaptation remains a question, demanding further experiments focusing on real-time evolution. Additionally, broader genetic analyses and microclimate studies may provide deeper insights into the traits and genes underlying adaptive potential at the southern range edge.