Evidence for recent evolution of cold tolerance in grasses suggests current distribution is not limited by (low) temperature

Abstract

Temperature is considered an important determinant of biodiversity distribution patterns. Grasses (Poaceae) occupy among the warmest and coldest environments on earth but the role of cold tolerance evolution in generating this distribution is understudied.
We studied cold tolerance of Danthonioideae (c. 280 species), a major constituent of the austral temperate grass flora. We determined differences in cold tolerance among species from different continents grown in a common winter garden and assessed the relationship between measured cold tolerance and that predicted by species ranges. We then used temperatures in current ranges and a phylogeny of 81% of the species to study the timing and mode of cold tolerance evolution across the subfamily.
Species ranges generally underestimate cold tolerance but are still a meaningful representation of differences in cold tolerance among species. We infer cold tolerance evolution to have commenced at the onset of danthonioid diversification, subsequently increasing in both pace and extent in certain lineages. Interspecific variation in cold tolerance is better accounted for by spatial than phylogenetic distance.
Contrary to expectations, temperature – low temperature in particular – appears not to limit the distribution of this temperate clade. Competition, time or dispersal limitation could explain its relative absence from northern temperate regions.