TY - JOUR T1 - The grass subfamily Pooideae: late Cretaceous origin and climate-driven Cenozoic diversification JF - bioRxiv DO - 10.1101/462440 SP - 462440 A2 - , Y1 - 2018/01/01 UR - http://biorxiv.org/content/early/2018/11/06/462440.abstract N2 - Aim Frost is among the most dramatic stresses a plant can experience and complex physiological adaptations are needed to endure long periods of sub-zero temperatures. Due to the need for evolving these complex adaptations, transitioning from tropical to temperate climates is regarded difficult and only half of the world’s seed plant families have temperate representatives. Here, we study the transition from tropical to temperate climates in the grass subfamily Pooideae, which dominates the northern temperate grass floras. Specifically, we investigate the role of climate cooling in diversification.Location Global, temperate regionsTime period Late Cretaceous-CenozoicMajor taxa The grass subfamily PooideaeMethods We date a comprehensive Pooideae phylogeny and test for the impact of paleoclimates on diversification rates. Using ancestral state reconstruction, we investigate if Pooideae ancestors experienced frost and winter. To locate the area of origin of Pooideae we perform biogeographical analyses.Results We estimated a late Cretaceous origin of the Pooideae (66 million years ago (Mya)), and all major clades had already diversified at the Eocene-Oligocene transition climate cooling (34 Mya). Climate cooling was a probable driving force of Pooideae diversification. Pooideae likely evolved in mountainous regions of southwestern Eurasia in a temperate niche experiencing frost, but not long winters.Main conclusion Pooideae originated in a temperate niche and experienced cold temperatures and frost long before the expansion of temperate biomes after the Eocene-Oligocene transition. This suggests that the Pooideae ancestor had adaptations to temperate climate and that extant Pooideae grasses share responses to low temperature stress in Pooideae. Throughout the Cenozoic falling temperatures triggered diversification. However, complex mechanisms for enduring strongly seasonal climate with long, cold winters most likely evolved independently in lower taxonomic lineages. Our findings provide insight into how adaptations to historic changes in chill and frost exposure influence distribution of plant diversity today. ER -