title: Key innovation or adaptive change? A test of leaf traits using Triodiinae in Australia.
abstract: The evolution of novel traits ("key innovations") allows some lineages to move into new environments or adapt to changing climates, whereas other lineages may track suitable habitat or go extinct. We test whether, and how, trait shifts are linked to environmental change using Triodiinae, C4 grasses that form the dominant understory over about 30% of Australia. Using phylogenetic and relaxed molecular clock estimates, we assess the Australian biogeographic origins of Triodiinae and reconstruct the evolution of stomatal and vascular bundle positioning. Triodiinae diversified from the mid-Miocene, coincident with the aridification of Australia. Subsequent niche shifts have been mostly from the Eremaean biome to the savannah, coincident with the expansion of the latter. Biome shifts are correlated with changes in leaf anatomy and radiations within Triodiinae are largely regional. Symplectrodia and Monodia are nested within Triodia. Rather than enabling biome shifts, convergent changes in leaf anatomy have probably occurred after taxa moved into the savannah biome-they are likely to have been subsequent adaptions rather than key innovations. Our study highlights the importance of testing the timing and origin of traits assumed to be phenotypic innovations that enabled ecological shifts.
authors.affiliation: School of Biological Sciences, The University of Queensland, Brisbane QLD 4072, Australia.
authors.forename: A
authors.initials: A
authors.lastname: Toon
authors.affiliation: Research School of Biology, The Australian National University, Canberra ACT 2601, Australia.
authors.forename: M D
authors.initials: MD
authors.lastname: Crisp
authors.affiliation: School of Agriculture and Food Sciences, The University of Queensland, Brisbane QLD 4072, Australia.
authors.forename: H
authors.initials: H
authors.lastname: Gamage
authors.affiliation: 1] School of Biological Sciences, The University of Queensland, Brisbane QLD 4072, Australia [2] Research School of Biology, The Australian National University, Canberra ACT 2601, Australia.
authors.forename: J
authors.initials: J
authors.lastname: Mant
authors.affiliation: Research School of Biology, The Australian National University, Canberra ACT 2601, Australia.
authors.forename: D C
authors.initials: DC
authors.lastname: Morris
authors.affiliation: School of Agriculture and Food Sciences, The University of Queensland, Brisbane QLD 4072, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Schmidt
authors.affiliation: School of Biological Sciences, The University of Queensland, Brisbane QLD 4072, Australia.
authors.forename: L G
authors.initials: LG
authors.lastname: Cook
mesh_terms: D001315:Australia; D018515:Plant Leaves / Q000033:anatomy & histology*; D006109:Poaceae / Q000145:classification / Q000502:physiology*; D013045:Species Specificity