Data from: Drought tolerance as an evolutionary precursor to frost and winter tolerance in grasses

Accumulating evidence is suggesting more frequent tropical-to-temperate
transitions than previously thought. This raises the possibility that
biome transitions could be facilitated by precursor traits. A wealth of
ecological, genetic and physiological evidence suggests overlap between
drought and frost stress responses, but the origin of this overlap, i.e.
the evolution of these responses relative to each other, is poorly known.
Here, we test whether adaptation to frost and/or severe winters in grasses
(Poaceae) was facilitated by ancestral adaptation to drought. We used
occurrence patterns across Köppen-Geiger climate zones to classify species
as drought, frost and/or winter tolerant, followed by comparative
analyses. Ancestral state reconstructions revealed different evolutionary
trajectories in different clades, suggesting both drought-first and
frost-first scenarios. Explicit simultaneous modelling of drought and
frost/winter tolerance provided some support for correlated evolution, but
suggested higher rates of gain of frost/winter tolerance in drought
sensitive rather than drought tolerant lineages. Overall, there is limited
support across grasses as a whole that drought tolerance acted as an
evolutionary precursor to frost or severe winter tolerance. Different
scenarios in different clades is consistent with present-day grasses being
either cold or drought specialists, possibly as a consequence of
trade-offs between different stress tolerance responses.