Life-history traits do not evolve in isolation because they jointly determine fitness. Their relative importance, however, can be modulated by local ecological demands. Co-variation between traits covering the major life-history phases, such as seed dormancy, flowering time and growth rate varies with latitude in A. thaliana (Debieu et al. 2013). This pattern is independent of population structure, suggesting that it may result from the action of selection. This work supports a model in which patterns of trait co-variation can respond to selection.

Further work in our laboratory has shown that, in A. thaliana, major changes in life-history strategies may impact plant investment into defense. Indeed, patterns of covariation between gene expression and flowering time indicate that alleles decreasing the expression level of defense genes are assorted with alleles accelerating the transition to flowering (Glander et al Gen Biol Evol 2018).

Patterns of trait co-variation thus allow making powerful inference of ecological diversity. To understand the ecological importance of variation in stomata size, we have examined covariation between stomata size and water-use efficiency under non limiting water supply. We show that smaller stomata improve water-use efficiency (Dittberner et al. Mol Ecol 2018). Using genome-wide associations (GWAS), we observed that stomata size is a polygenic trait that contributes to optimize water-use efficiency in regions of the species range where escape strategies such as accelerated flowering time cannot be implemented.

We are currently expanding this work to understand the genetic underpinning and adaptive relevance of variation in growth rate and its co-variates across A. thaliana populations from Northern and Southern Europe.