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SSStttooonnnyyy BBBrrrooooookkk UUUnnniiivvveeerrrsssiiitttyyy The official electronic file of this thesis or dissertation is maintained by the University Libraries on behalf of The Graduate School at Stony Brook University. ©©© AAAllllll RRRiiiggghhhtttsss RRReeessseeerrrvvveeeddd bbbyyy AAAuuuttthhhooorrr... Form, Function, and Phylogeny: Angiosperm Leaf Trait Evolution, with a Case Study in the Genus Dioscorea A Dissertation Presented by Ramona Lynn Walls to The Graduate School in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Ecology and Evolution Stony Brook University December 2009 Copyright by Ramona Lynn Walls 2009 Stony Brook University The Graduate School Ramona Lynn Walls We, the dissertation committee for the above candidate for the Doctor of Philosophy Degree, hereby recommend acceptance of this dissertation. R. Geeta - Dissertation Advisor Associate Professor, Department of Ecology and Evolution, Stony Brook University Massimo Pigliucci - Chairperson of the Defense Professor, Department of Ecology and Evolution, Stony Brook University Catherine Graham Assistant Professor, Department of Ecology and Evolution, Stony Brook University Manuel Lerdau Professor, Departments of Environmental Sciences and Biology, University of Virginia Noel Michele Holbrook Professor, Department of Organismic and Evolutionary Biology, Harvard University This dissertation is accepted by the Graduate School Lawrence Martin Dean of the Graduate School ii Abstract of the Dissertation Form, function, and phylogeny: Angiosperm leaf trait evolution, with a case study in the genus Dioscorea By Ramona Lynn Walls Doctor of Philosophy in Ecology and Evolution Stony Brook University 2009 Broad-scale correlations among leaf traits or between leaf traits and the environment support the hypothesis that natural selection in response to climate has played a major role in plant diversification. Yet species and leaf trait diversity is ultimately the result of divergences among closely related species. I examined trait relationships across these two scales to compare the roles of evolutionary history and natural selection in the diversification of leaf forms. This first chapter of this dissertation provides the first global-scale, phylogenetically based demonstration of relationships between leaf vein patterns and leaf functions in angiosperms. Minor vein density was significantly correlated with maximum photosynthetic rate, supporting the hypothesis of correlated evolution of leaf hydraulic capacity and photosynthetic ability. Evolutionary shifts in secondary vein type were accompanied by shifts in leaf life span, suggesting an adaptive relationship that is consistent with previously observed relationships between leaf form and climate. In contrast, the relationship between primary vein type and maximum photosynthetic rate appears to reflect the phylogenetic distribution of leaf traits, rather than adaptive co-evolution. The second chapter was at a narrower phylogenetic scale, but broad geographic scale. I examined relationships among leaf traits that are important for gas exchange and water delivery within the genus Dioscorea, and compared them to expectations from large-phylogenetic-scale studies. Some relationships within this genus were consistent with large-scale studies, while others were strikingly different and may indicate constraints among close relatives. This suggests that how species diversify along leaf trait co-variation axes will depend on the unique combinations of traits and ecological challenges present in different lineages. The third chapter examined a different set of 20 Dioscorea species collected from Mexico. I determined that species’ values of many leaf functional traits were correlated with the climate in which they occur using standard correlation methods, but not using phylogenetically-based methods. The same set of traits, and climate parameters were phylogenetically conserved. These results suggest that while these leaf traits are important for adaptation to climate, their current association with climate is a result of earlier adaptation followed by niche conservatism, iii rather than repeated adaptive evolution. The traits that I expected to be under selection by micro-environmental factors were not significantly correlated with climate parameters using either method and were not phylogenetically conserved. The relationship between whether or not traits were correlated with climate and whether or not they were phylogenetically conserved supports the notion that niche conservatism is tightly linked to functional trait conservatism. The combination of conserved traits and niches at one scale with labile traits and niches at another be responsible for the high diversity of Mexican Dioscorea species. The research presented in this dissertation demonstrates how the complementary processes of change (adaptive evolution) and lack of change (phylogenetic conservatism) may act together to generate biodiversity. iv Table of Contents List of Symbols and Abbreviations……………………………………………………...vii List of Figures….………………………………………………………………………....ix List of Tables…………………………………………………………………………….xii Acknowledgements……………………………………………………………………..xiii Introduction: Form, function, and phylogeny: Why are there so many different leaf forms?……………………………………………………………………………………..1 Literature Cited……………………………………………………………………5 Chapter 1: Phylogeny and adaptation in the evolution of angiosperm vein patterns……..8 Abstract..……………………..………………………………………………..…..8 Introduction………………..………………………………………………………8 Methods…………………………………………………………………………..11 Results……………………………………………………………………………12 Discussion………………………………………………………………………..13 Acknowledgments………………………………………………………………..17 Literature Cited…………………………………………………………………..18 Tables…………………………………………………………………………….22 Figure Legends…..……………………………………………………………….23 Figures……………………………………………………………………………24 Chapter 2: Trait correlations across phylogenetic scales: Stomatal traits and leaf size affect leaf function in unexpected ways in the genus Dioscorea ………………………..28 Abstract..……………………..…………………………………………………..28 Introduction………………..……………………………………………………..28 Methods…………………………………………………………………………..31 v Results……………………………………………………………………………34 Discussion………………………………………………………………………..36 Acknowledgments…………………………………………………………….….43 Literature Cited…………………………………………………………………..44 Tables…………………………………………………………………………….50 Figure Legends…..……………………………………………………………….52 Figures……………………………………………………………………………54 Chapter 3: Leaf functional traits, climate niches, and phylogenetic conservatism in Mexican Dioscorea species……………………………………..………………………..66 Abstract..……………………..…………………………………………………..66 Introduction………………..……………………………………………………..66 Methods…………………………………………………………………………..68 Results……………………………………………………………………………73 Discussion………………………………………………………………………..75 Acknowledgments……………………………………………………………….80 Literature Cited…………………………………………………………………..81 Tables…………………………………………………………………………….85 Figure Legends…..…………….…………………………………………………90 Figures…………………………..………………………………………………..91 Conclusions…………………………………………………………………………….…94 Literature Cited…………………………………………………………………..98 Bibliography……………………………………………………………………………..99 Appendices……………………………………………………………………………..116 vi List of Symbols and Abbreviations Term Definition Units -2 -1 Aarea maximum photosynthetic rate on an area μmol CO2 m sec basis (Chapter 1 or 2) -1 -1 Amass maximum photosynthetic rate on a mass nmol CO2 g sec basis (Chapter 1) -1 -1 Amax maximum photosynthetic rate on a mass μmol CO2 g sec basis (Chapter 2) Capacitance change in relative water content with MPa-1 change in water potential, a measure of leaf water holding capacity ci leaf internal CO2 concentration not used in this document GCL guard cell length mm -2 -1 gmin minimum conductance, also cuticular mmol H2O m sec conductance. Loss of water per time of leaves with fully closed stomata -2 -1 gs stomatal conductance mol H2O m sec Kleaf leaf hydraulic conductance Mpa-1 m-2 sec-1 -1 -1 3 Kt-mr theoretical midrib conductivity (function mmol m Mpa sec x 10 of the number of midrib conduits and their size) Lamina area lamina area cm2 LLS leaf life span months LMA leaf mass per area g m-2 L:W length to width ratio unitless MR TE area average area of the tracheary elements in mm the midrib MR VB area cross-sectional area of the midrib vascular mm bundle MVD minor vein density mm mm-2 N content, %N nitrogen content of dry leaves unitless -2 Narea N content on an area basis g m Nmass N content on a mass basis, same as N unitless content or %N Pet area cross-sectional area of the petiole mm2 Pet VB area cross-sectional area of all vascular mm bundles in the petiole PVD primary vein density cm cm-2 RWC Relative water content unitless SD stomatal density #stomata mm-2 SI stomtal index #stomata/#guard cells SPI stomatal pore index (SDxGLC^2) unitless vii WC water content (mass of water/wet mass at unitless full turgor) -1 WUEinst instantaneous water use efficiency μmol CO2 mol H20 Ψmin leaf minimum water potential MPa δ13C carbon isotope discrimination parts per thousand (unitless) viii List of Figures Chapter 1 Fig. 1. Schematic representation of A. primary and B. secondary vein patterns. These illustrations represent possible leaf shape/vein type combinations, but there were different shapes within each category.……………………………………………………………..24 Fig. 2. Box plots of primary vein type versus A. Amass, B. Nmass, and C. LMA. Lower case letters indicate statistically similar values among categories, using standard ANOVA. Upper case letters indicate