Leaf shape and size track habitat transitions across forest–grassland boundaries in the grass family (Poaceae)

Abstract

Grass leaf shape is a strong indicator of their habitat with linear leaves predominating in open areas and ovate leaves distinguishing forest‐associated grasses. This pattern among extant species suggests that ancestral shifts between forest and open habitats may have coincided with changes in leaf shape or size. We tested relationships between habitat, climate, photosynthetic pathway, and leaf shape and size in a phylogenetic framework to evaluate drivers of leaf shape and size variation over the evolutionary history of the family. We also estimated the ancestral habitat of Poaceae and tested whether forest margins served as transitional zones for shifts between forests and grasslands. We found that grass leaf shape is converging toward different shape optima in the forest understory, forest margins, and open habitats. Leaf size also varies with habitat. Grasses have smaller leaves in open and drier areas, and in areas with high solar irradiance. Direct transitions between linear and ovate leaves are rare as are direct shifts between forest and open habitats. The most likely ancestral habitat of the family was the forest understory and forest margins along with an intermediate leaf shape served as important transitional habitat and morphology, respectively, for subsequent shifts across forest–grassland biome boundaries.

High silicon concentrations in grasses are linked to environmental conditions and not associated with C4 photosynthesis

“…Inference about broad trends in the evolution of Si concentration may additionally run into complications related to long‐term changes in the Earth's climate and atmosphere. Climatic conditions have changed substantially over ~100 million years since grasses first evolved and began to diversify (Gallaher et al., 2019; Strömberg, 2011; Zachos, Dickens, & Zeebe, 2008), and it is possible that entirely non‐analog conditions existed on Earth during this time (e.g., see discussion in Dunn et al., 2015). Consequently, inferences based on extant grasses growing under modern climatic regimes may not be wholly reliable for reconstructing patterns in the past.…”

Continued Adaptation of C4 Photosynthesis After an Initial Burst of Changes in the Andropogoneae Grasses

“…In previous grass phylogenetic trees, Andropogoneae formed a large clade entirely composed of C \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} species, and its closest known C \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{3}$\end{document} relatives belonged to a different group containing multiple independent C \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} lineages ( GPWG II 2012 ; Gallaher et al 2019 ). The branch leading to Andropogoneae was, therefore, long, preventing the precise inference of changes leading to C \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} evolution in this group.…”

“…Besides generating some of the most productive plants in the world, their C \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} trait also increased the diversification of Andropogoneae, which in turn has shaped ecosystems around the world ( Osborne 2008 ; Edwards et al 2010 ; Forrestel et al 2014 ; Spriggs et al 2014 ; Sage and Stata 2015 ). Because 1) they are separated from other C \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} grass lineages in the phylogeny by several C \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{3}$\end{document} branches ( Grass Phylogeny Working Group II GPWG II 2012 and 2) the different C \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} lineages differ in the underlying genetic changes, Andropogoneae are accepted as a C \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} origin independent from those in other groups of grasses ( Sinha and Kellogg 1996 ; Christin et al 2008 , Christin et al 2010 ; Vicentini et al 2008 ; Edwards and Smith 2010 ; Sage et al 2011 ; GPWG II 2012 ; Emms et al 2016 ; Gallaher et al 2019 ; Niklaus and Kelly 2019 ).…”

3D shape analysis of grass silica short cell phytoliths: a new method for fossil classification and analysis of shape evolution

“…The average number of transitions between states over 5000 simulations were calculated. We used the plastome-based phylogenetic trees of Gallaher et al (2019), dropping the tips of taxa not represented by phytolith data. There are two major alternate phylogenetic hypotheses for the relationships among Bambusoideae tribes (Triplett et al, 2014;Guo et al, 2019).…”