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.

A molecular phylogeny and classification of the Cynodonteae (Poaceae: Chloridoideae) with four new genera: Orthacanthus, Triplasiella, Tripogonella, and Zaqiqah; three new subtribes: Dactylocteniinae, Orininae, and Zaqiqahinae; and a subgeneric classification of Distichlis

“…-Early molecular DNA studies of Trioidia s.str. suggesting that the genus is monophyletic (Mant & al., 2000;Peterson & al., 2010a) have been verified recently by extensive sampling that included 66 of the 69 species in the genus (Toon & al., 2015). We include 22 species in our strongly supported Triodia clade (BS = 100, PP = 1.00) that is sister to the Aeluropodinae and the Orininae.…”

Initial Expansion of C4 Vegetation in Australia During the Late Pliocene

“…C 33 is therefore proposed to be more sensitive to the presence of C 4 grasses on the landscape (Uno et al, 2016), while C 29 is less influenced by grasses. Phylogenetic evidence suggests that the moderately diverse C 4 grass tribe Triodiinae, characteristic of central Australian arid vegetation today, radiated in the Australian interior during the late Miocene (Toon et al, 2015). Phylogenetic evidence suggests that the moderately diverse C 4 grass tribe Triodiinae, characteristic of central Australian arid vegetation today, radiated in the Australian interior during the late Miocene (Toon et al, 2015).…”

Increased diversification rates are coupled with higher rates of climate space exploration in Australian Acacia (Caesalpinioideae)

“…At that time only the north-west displayed aridity, though central Australia likely had seasonal dryness (Martin, 2006;Huber & Goldner, 2012). Since the Eocene, Australia's climate has progressively dried, presenting ecological opportunities and resulting in spectacular radiations within one or more of the Australian biomes (Crayn et al, 2006;Rabosky et al, 2007;Crisp et al, 2009;Sanders et al, 2008;Watanabe et al, 2006;Catullo & Keogh, 2014;Toon et al, 2015;Lamont et al, 2016;Brennan & Oliver, 2017). For example, Australian rainforests now occupy a small fraction of their former extent, and many rainforest lineages are now extinct (Hill et al, 1999;Martin, 2006;Byrne et al, 2008Byrne et al, , 2011.…”