Recent evolution of flowering time across multiple European plant species correlates with changes in aridity - Greenhouse data

Ongoing global warming and increased drought frequencies have a large impact on plant populations and potentially drive evolutionary adaptations. Historical comparisons, where plants grown from seeds collected in the past (“ancestors”) are compared to plants grown from freshly collected seeds from the same populations (“descendants”), are a powerful method to investigate such evolutionary changes across many taxa. When applied to multiple species simultaneously, historical comparisons can reveal recent parallel evolutionary shifts. We used 21-38 year old seeds of 13 European plant species, stored in seed banks and originating from Mediterranean and temperate regions, for a greenhouse experiment that investigated shifts of flowering phenology, as a potential result of adaptive evolution to increased drought over the last decades. We additionally used single nucleotide polymorphism (SNP) markers to quantify relatedness and levels of genetic variation, and to characterize potential neutral processes and differences in sampling schemes. We found that, across species, descendants grew faster and advanced their flowering, and that these shifts were correlated with changes in aridity at the population origins, suggesting that drought induced evolution of earlier flowering. In 6 out of the 13 species, however, the SNP markers detected strong differences in genetic variation and relatedness between ancestors and descendants, indicating that other evolutionary processes may have contributed to genetic changes. Our results suggest that changes in aridity due climate change may have influenced the evolutionary trajectories of many plant species in different regions of Europe, and that flowering phenology may be one of the key traits that is rapidly evolving. Our study provides further evidence that seed bank collections, with some limitations, are a largely untapped resource for investigating the impact of global environmental changes on plant populations.