Evolutionary footprints of a cold relic in a rapidly warming world

With accelerating global warming, understanding the evolutionary dynamics
of plant adaptation to environmental change is increasingly urgent. Here
we reveal the enigmatic history of the genus Cochlearia (Brassicaceae), a
Pleistocene relic that originated from a drought-adapted Mediterranean
sister genus during the Miocene. Cochlearia rapidly diversified and
adapted to circum-Arctic regions and other cold-characterized habitat
types during the Pleistocene. This sudden change in ecological preferences
was accompanied by a highly complex, reticulate polyploid evolution, which
was apparently triggered by the impact of repeated Pleistocene glaciation
cycles. Our results illustrate that two early diversified arctic-alpine
diploid gene pools contributed differently to the evolution of this young
polyploid genus now captured in a cold-adapted niche. Metabolomics
revealed central carbon metabolism responses to cold in diverse species
and ecotypes, likely due to continuous connections to cold habitats that
may have facilitated widespread adaptation to alpine and subalpine
habitats, and which we speculate were coopted from existing drought
adaptations. Given the growing scientific interest in adaptive evolution
of temperature-related traits, our results provide much-needed taxonomic
and phylogenomic resolution of a model system as well as first insights
into the origins of its adaptation to cold.