An evolutionary perspective on leaf economics: phylogenetics of leaf mass per area in vascular plants Olivier Flores1,2, Eric Garnier1, Ian J. Wright3, Peter B. Reich4,5, Simon Pierce6, Sandra Dıaz7, Robin J. Pakeman8, Graciela M. Rusch9, Maud Bernard-Verdier1, Baptiste Testi1, Jan P. Bakker10, Renee M. Bekker10, Bruno E. L. Cerabolini11, Roberta M. Ceriani12, Guillaume Cornu13, Pablo Cruz14, Matthieu Delcamp13, Jiri Dolezal15, Ove Eriksson16, Adeline Fayolle13, Helena Freitas17, Carly Golodets18, Sylvie Gourlet-Fleury13, John G. Hodgson19, Guido Brusa11, Michael Kleyer20, Dieter Kunzmann20,21, Sandra Lavorel22, Vasilios P. Papanastasis23, Natalia Perez-Harguindeguy 7, Fernanda Vendramini7 & Evan Weiher24 1CNRS, Centre d’Ecologie Fonctionnelle et Evolutive (CEFE), UMR 5175, 1919 route de Mende, 34293 Montpellier Cedex 5, France 2UMR PVMBT, UniversitedelaR eunion, CIRAD, 7 chemin de l’IRAT, 94710 Saint–Pierre, France 3Department of Biological Sciences, Macquarie University, New South Wales 2109, Australia 4Department of Forest Resources and Institute on the Environment, University of Minnesota, St Paul, Minnesota 5Hawkesbury Institute for the Environment, University of Western Sydney, Hawkesbury, New South Wales, Australia 6Department of Plant Production, University of Milan, via Celoria 2, I-20133 Milan, Italy 7Instituto Multidisciplinario de Biologıa Vegetal (CONICET - UNC) and FCEFyN, Universidad Nacional de Cordoba, Casilla de Correo 495, Velez Sarsfield 299, 5000 Cordoba, Argentina 8James Hutton Institute, Craigiebuckler, Aberdeen, AB15 8QH, UK 9Norwegian Institute for Nature Research, Tungasletta 2, 7485 Trondheim, Norway 10Community and Conservation Ecology Group, PO Box 14, 9750 AA Haren, The Netherlands 11DBSF, Universita degli Studi dell’Insubria, Via J.H. Dunant 3, I- 21100 Varese, Italy 12Centro Flora Autoctona, c/o Consorzio Parco Monte Barro, via Bertarelli 11, I-23851 Galbiate (LC), Italy 13UR B&SEF CIRAD, TA C-105/D, Campus International de Baillarguet, 34398 Montpellier Cedex 5, France 14INRA UMR 1248 AGIR, Equipe ORPHEE, BP 52627 - Auzeville, 31326 Castanet-Tolosan, France 15Institute of Botany, Academy of Sciences of the Czech Republic, Dukelska 135, CZ-37982, Trebon, Czech Republic 16Department of Botany, Stockholm University, Stockholm 106 91, Sweden 17Centre for Functional Ecology, University of Coimbra, Coimbra, Portugal 18Department of Molecular Biology and Ecology of Plants, Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel 19Department of Archaeology, The University, Sheffield S1 4ET, UK 20Landscape Ecology Group, Carl von Ossietzky University of Oldenburg, P.O. Box 2503, 26111 Oldenburg, Germany 21Landscape Ecology & Consulting, Lerchenstrasse 20, 26215 Wiefelstede, Germany 22Laboratoire d’Ecologie Alpine (CNRS UMR 5553) and Station Alpine Joseph Fourier (UMS-UJF-CNRS 2925), Universite Joseph Fourier, BP 53, F-38042 Grenoble, Cedex 09, France 23Laboratory of Rangeland Ecology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece 24Department of Biology, University of Wisconsin-Eau Claire, Phillips Hall 353, Eau Claire, Wisconsin 4702-4004 Keywords Brownian model, functional trait, Ornstein– Uhlenbeck model, phenotypic evolution. Abstract In plant leaves, resource use follows a trade-off between rapid resource capture Correspondence Olivier Flores, CNRS, Centre d’Ecologie and conservative storage. This “worldwide leaf economics spectrum” consists of Fonctionnelle et Evolutive (CEFE), UMR 5175, a suite of intercorrelated leaf traits, among which leaf mass per area, LMA, is 1919 route de Mende, 34293 Montpellier one of the most fundamental as it indicates the cost of leaf construction and Cedex 5, France. light-interception borne by plants. We conducted a broad-scale analysis of the Tel: +262 262 499 250; evolutionary history of LMA across a large dataset of 5401 vascular plant spe- + Fax: 262 262 499 293; cies. The phylogenetic signal in LMA displayed low but significant conserva- E-mail: olivier.fl[email protected] tism, that is, leaf economics tended to be more similar among close relatives than expected by chance alone. Models of trait evolution indicated that LMA Funding Information evolved under weak stabilizing selection. Moreover, results suggest that different This work was supported by the ANR project optimal phenotypes evolved among large clades within which extremes tended A-BI-ME (Activites humaines, dynamique et to be selected against. Conservatism in LMA was strongly related to growth gestion de la BIodiversite en milieu form, as were selection intensity and phenotypic evolutionary rates: woody – MEditerraneen, ANR-05-BDIV-014, 2006 plants showed higher conservatism in relation to stronger stabilizing selection 2008). ª 2014 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. 2799 This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. An Evolutionary Perspective on Leaf Economics O. Flores et al. Received: 3 October 2013; Revised: 28 and lower evolutionary rates compared to herbaceous taxa. The evolutionary March 2014; Accepted: 2 April 2014 history of LMA thus paints different evolutionary trajectories of vascular plant species across clades, revealing the coordination of leaf trait evolution with – Ecology and Evolution 2014; 4(14): 2799 growth forms in response to varying selection regimes. 2811 doi: 10.1002/ece3.1087 Introduction LMA would have evolved under strong selection and be conserved along plant lineages, which would generate a Although leaf morphology has evolved manifold varia- consistent and detectable phylogenetic signal. tions across vascular plant species, there is strong evi- Phylogenetic signal can be broadly defined as the infor- dence of a universal spectrum constraining leaf mation conveyed by the variation in phenotypic trait val- functioning from rapid resource capture to efficient ues within and across clades along a phylogeny. In the resource use (Grime et al. 1997; Reich et al. 1997; Dıaz present study, we conducted a comprehensive analysis of et al. 2004; Wright et al. 2004). This worldwide leaf eco- the evolutionary history of leaf economics across the phy- nomics spectrum (Wright et al. 2004) consists of the cor- logeny of vascular plants based on the analysis of the phy- related variation among several key plant traits, including logenetic signal in LMA. Variation in trait similarity leaf mass per area (LMA, the ratio between leaf dry mass among taxa may reveal patterns of either trait diversifica- and leaf area) which describes the dry mass investment tion or trait conservatism within clades, that is, the ten- for light interception per unit leaf area (Lambers and dency for relatives to be more similar than expected by Poorter, 1992). LMA captures a central axis of functional chance alone. Such macroevolutionary patterns may pro- variation in plants (Grime et al. 1997; Grime 2001; West- vide insight into the microevolutionary processes (e.g., oby et al. 2002; Dıaz et al. 2004), correlating negatively selection and drift) shaping trait evolution within lineages with mass-based photosynthetic rate and leaf macronutri- (Hansen and Martins, 1996; Hansen 1997; Diniz-Filho ent concentrations (Reich et al. 1997; Wright et al. 2004), 2001). and positively with leaf life span (Wright et al. 2004). At Variation in leaf mass per area was charted across a dated large spatial scales, LMA varies across climatic gradients, phylogeny of 5401 species spanning all major clades of vas- displaying on average higher values in hotter, drier, and cular plants. Using phylogenetic comparative analyses, we higher irradiance habitats, particularly once other factors, analyzed the phylogenetic signal in LMA and compared such as deciduousness or plant functional type composi- observed patterns to expectations based on different models tion, are taken into account (Reich et al. 1997; Wright of trait evolution. We show that LMA exhibits low but sig- et al. 2004; Reich et al. 2007; Poorter et al. 2009). nificant overall phylogenetic conservatism across vascular Despite a sound knowledge of the physiological and plant clades. We identify different clades displaying signifi- ecological correlates of LMA, we remain largely ignorant cant phylogenetic patterns of either trait conservatism or of the evolutionary history that gave rise to the present- diversification. Moreover, we tested the interaction between day wide variation in this key trait. Two types of overall the evolutionary histories of LMA and growth form across evolutionary behavior may be expected for a vegetative species. We note that potential additional explanatory vari- trait such as LMA: it can either be evolutionary labile and ables such as biogeography or pedo-climatic conditions vary independently from the phylogeny across species, were outside the scope of the present study. We found that which can lead to high functional convergence across patterns of LMA evolution consistently differed across clades (Kraft et al. 2007), or it may alternatively display growth forms, revealing evidence for a higher conservatism phylogenetic patterns structured by selection within plant and slower trait evolution in woody species than in herba- lineages (Blomberg et al. 2003; Losos 2008). In the labile ceous species. trait hypothesis, we nonetheless expect consistent evolu- tion with other plant traits, or syndromes such as growth Material and Methods