Leaf traits of Ficus: an evolutionary prespective

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A presentation for the 2013 Applied Fieldcourse in Ecology and Evolution at the Xishuangbanna Tropical Botanical Garden.

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  • Good afternoon everyone! We will talk to you today about Leaf variation in Ficus, with an evolutionary perspective
  • Here’s our outline: YaoXin will introduce leaf diversity and Ficus, I, Si-Jin, will present our hypothesis, Huyen will tell you what we did, Wu Wei Huan will tell you what we found, and Gao Lao will discuss our findings.
  • Leaves are the organs primarily responsible for all photosynthesis. However, they often exhibit remarkable diversity. For example, this picture shows the diversity of leaves in the South African genus Pelargonium. The patterns of this diversity are not well understood
  • Ficus is a large pantropical genus, which has more than 800 species.There is a lot of diversity in Ficus, but today, we will focus on two aspects: Life history diversity, and leaf diversity
  • Our first focus is life history diversity in Ficus. A lot of Figs are hemi-epiphytic; in fact, the hemi epiphytic life style is thought to have evolved four times in this genus.Individuals of hemiepiphytes star their lives on tree branches, as shown in this picture. Many studies have shown that during this stage, hemiepiphytic figs often experience a lot of water stress, because their roots are not in the ground.Eventually, the roots take hold in the ground, and the water stresses may be different.
  • Leaves in Ficus are very diverse: this picture shows a set of leaves collected within XTBG. We can see variation in size, shape, morphology, and texture. Today, we will focus on leaf size.
  • Thinking about leaf size, we might expect that because big leaves are heavier, they require more structure to hold up. Structure can come in many ways, including vein structure and lamina toughness. Today, we will focus on lamina toughness of large leaves. We can also expect that for a species to evolve large leaves, the ancestral individuals also needed to have tough leaves.
  • So, based on what Yao Xin has introduced about Ficus, we can have two hypotheses. First, we can expect hemiepiphytes to have evolved to deal with water stressed environments. This hypothesis leads to a prediction that hemiepiphytes will have lower leaves with lower SLA, even when grown in common gardens with terrestrial figs. We can also hypothesize that because large leaves are harder to hold up, they will be tougher. We can test this by describing the relationship between leaf size and toughness. We also expect patterns of correlated evolution between these two traits.
  • Our study was conducted in Xishuangbanna Tropical Botanical Garden, Fig Collection , grow under same environmental conditions  common garden setting
  • For 3 prediction Reconstructed Ancestral trait of LA and toughness and use Phylogenetically Independent Contrasts to examined the co-evolution between them
  • These are our raw results, which show the variation of SLA, area,and toughness. The variation in area is huge, but SLA and toughness have less variation.
  • Here, we show the results of our test of prediction 1. We did not find significant difference in the leaf area and SLA of hemiepiphytic and terrestrial figs.
  • Here, we show the results of our test of prediction 2. Leaf size and lamina toughness do not show any significant relationship
  • Here, we show the results of our test of Prediction 3. This figure shows the estimates of area and toughness across the phylogeny. A dark blue color indicates that leaves are smaller or weaker; red indicate larger or stronger leaves. These two boxes seem to suggest that the patterns of trait evolution are not exactly similar.To statistically test whether the patterns of leaf area evolution and toughness are related, we calculated the PICs of leaf area and toughness. PICs are related to the rate of trait evolution across the phylogeny.If the patterns of leaf area change and toughness change are related, we will expect a significant relationship between the PICs of leaf area and the PICs of toughness.
  • Here is the graph of Area PICs and Toughness PICs. We did not find any significant relationship.
  • Our first prediction, that hemiepiphytic figs have smaller leaves with lower SLA compared to terrestrial figs, was not supported. This is in contrast to many other studies that have found this relationship; however, our study was uniquely conducted in a common garden setting. This suggests that environmental factors are driving the differences observed in nature. Although hemiepiphytes do not appear to be biologically predisposed to having leaves adapted for stress, they may have evolved other mechanisms to cope with water stress. For example, xylem water conductivity, and veins architecture may be different between hemiepiphytes and terresrials.
  • Our second prediction, that larger leaves need to be stronger to be held up against gravity, was not supported. It is possible that the large leaves are held up primarily to the architecture of their veins and petioles, which were not considered in our study.We also found no support for our third prediction that leaf size and toughness have undergone correlated evolution. This makes sense in light of prediction 2, because the two traits are not correlated at the tips of the phylogeny, so they are unlikely to be correlated in their evoutionary histories. Before we propose some directions for future research, we would like to acknowledge some limitations of our study.
  • First off, our sampling intensity might not have accounted for intraspecific variation in the measured leaf traits, so we may not have approximated the true species means. Second, our test of Hypothesis I was unbalanced, as we had only 8 hemiepiphytic and 22 epiphytic fig species.And finally, all of our tests that involved using the phylogeny were limited because the Ficus phylogeny is not completely resolved. Our methods are sensitive to the toplogy and branch lengths of the tree, so they may change with any major change in the ficus phylogeny.
  • And now, we would like to offer some potential avenues of research. First off, because leaves are the organs that harvest all light energy into chemical energy, we think that it is very worthwhile to study their evolutionary patterns, which are not currently well understood.
  • Leaf traits of Ficus: an evolutionary prespective

    1. 1. Leaf variation in Ficus: an evolutionary perspective Kandlikar Gau-Lou Nguyen Hai Huyen Wu Wei-Huan Yao Xin Zeng Si-Jin 28 November 2013
    2. 2. Outline • • • • • Introduction to leaf diversity and Ficus Our hypotheses How we tested them What we found What it means 2
    3. 3. Leaf diversity • Leaves are the organs primarily responsible for photosynthesis • Evolutionary patterns of leaf variation are not well understood (Jones et al. 2008) Leaf variation in Pelargonium. Image from Nicotra et al. 2011 3
    4. 4. Introduction to Ficus • Ficus is a large pan-tropical genus with >800 species • Lot of variation in life history patterns and ecology, with an equally complex evolutionary history (Harrison 2005) • Leaves within the genus exhibit tremendous diversity 4
    5. 5. Hemiepiphytic Ficus • Many Ficus species have a “hemi-epiphytic” life style • Epiphytic stage associated with water stress (Holbrook & Putz 1996, Hao et al. 2010) Epiphytic and Terrestrial F. concinna, from Hao G.Y., et al. 2010 5
    6. 6. Leaf variation in Ficus 6
    7. 7. Leaf size variation • Large leaves require more “structure” to hold up against gravity (Niklas 1999) – Structure might come in many ways (Westbrook et al., 2012) • For large leaves to evolve, ancestors needed to have leaves with greater structure 7
    8. 8. Hypotheses • HI: Hemiepiphytic figs have evolved to deal with water stressed environments – Prediction: Hemiepiphytic figs have smaller leaves with lower specific leaf area (SLA), even when grown in common gardens with terrestrial figs • HII: Large leaves are harder to hold up than small leaves; thus they need to be tougher – Prediction: Leaf size ~ Leaf lamina toughness – Prediction: Leaf size and leaf toughness show patterns of correlated evolution 8
    9. 9. Study site • Xishuangbanna Tropical Botanical Garden = sampled individuals Ficus collection 9
    10. 10. Methods • Sampling intensity: – 2 trees/species; 3 leaves/tree • Leaf traits measurements according to published protocols (Perez-Harguindeguy et al. 2013) – Leaf Area, Toughness, and SLA • Life history data (i.e. epiphytic/terrestrial) collected from the Flora of China (eFloras 2008) 10
    11. 11. F hispida F fistulosa F semicordata ● F sur F beipeiensis F auriculata F oligodon Phylogenetic Methods • Used a published Ficus phylogeny (Cruaud et al. ● F racemosa F tikoua F villosa F sarmentosa F deltoidea F stenophylla F ischnopoda F hirta F ruficaulis F tinctoria F subulata F cyrtophylla F henryi ● 2012) • Thirty species shared between XTBG Ficus collection and the phylogeny ● ● F concinna F cyathistipula ● ● F virens F religiosa ● ● ● ● F stricta ● F maclellandii F benjamina ● ● ● F altissima F annulata F glaberrima ● ● ● 11
    12. 12. Data Analysis • Testing prediction 1 – T-Tests to compare leaf area and SLA of HE/Ter • Testing prediction 2 – Test for relationship between Leaf Area and Toughness • Testing prediction 3 – Ancestral Trait Reconstruction and Phylogenetically Independent Contrasts (PICs) of Area and Toughness in R package phytools (Felsenstein 1985; Revell 2012) 12
    13. 13. Results F hispida F fistulosa F semicordata F sur F beipeiensis F auriculata F oligodon F racemosa F tikoua F villosa F sarmentosa F deltoidea F stenophylla F ischnopoda F hirta F ruficaulis F tinctoria F subulata F cyrtophylla F henryi F virens F religiosa F concinna F cyathistipula F stricta F maclellandii F benjamina F altissima F annulata F glaberrima SLA Area Toughness 13
    14. 14. Results • Prediction 1 (Hemiepiphytes ~ smaller leaves with low SLA) Log Area of HE and Terrestrial Ficus species SLA of HE and epiphytic and terrestrial Ficus specie SLA variation between Terrestrial Ficus species 250 p=0.40 200 150 SLA 5 100 4 3 Area log logArea 6 p=0.90 Epi Ter Epi Ter 14
    15. 15. Results, cont. • Prediction 2 (Leaf area ~ Leaf toughness) Log Area vs. Toughness 5 4 3 log Area (cm^2) 6 p=0.91 200 400 600 800 1000 1200 1400 Toughness (N/m^2) 15
    16. 16. Results, cont. • Prediction 3 (Leaf area ~ Leaf toughness across the phylogeny) 16
    17. 17. Reconstruction of Toughness Reconstruction of log Area F hispida F hispida F hispida F hispida F fistulosa F fistulosa F fistulosa F fistulosa F semicordata F semicordata F semicordata F semicordata F sur F sur F sur F sur F beipeiensis F beipeiensis F beipeiensis F beipeiensis F auriculata F auriculata F auriculata F auriculata F oligodon F oligodon F oligodon F oligodon F racemosa F racemosa F racemosa F racemosa F tikoua F tikoua F tikoua F tikoua F villosa F villosa F villosa F villosa F sarmentosa F sarmentosa F sarmentosa F sarmentosa F deltoidea F deltoidea F deltoidea F deltoidea F stenophylla F stenophylla F stenophylla F stenophylla F ischnopoda F ischnopoda F ischnopoda F ischnopoda F hirta F hirta F hirta F hirta F ruficaulis F ruficaulis F ruficaulis F ruficaulis F tinctoria F tinctoria F tinctoria F tinctoria F subulata F subulata F subulata F subulata F cyrtophylla F cyrtophylla F cyrtophylla F cyrtophylla F henryi F henryi F henryi F henryi F virens F virens F virens F virens F religiosa F religiosa F religiosa F religiosa F concinna F concinna F concinna F concinna F cyathistipula F cyathistipula F cyathistipula F cyathistipula F stricta F stricta F stricta F stricta F maclellandii F maclellandii F maclellandii F maclellandii F benjamina F benjamina F benjamina F benjamina F altissima F altissima F altissima F altissima F annulata F annulata F annulata F annulata F glaberrima F glaberrima F glaberrima F glaberrima 3.05 trait value 6.787 6.787 2 20 cm3.05trait value 800 cm2 length=0.023 length=0.023 239.572 1374.305 239.572 200 grams trait value 1500 trait value 1374.305 length=0.023 length=0.023 grams 17
    18. 18. Results, cont. • Prediction 3 PICs of Log Area vs. PICs of Toughness 1 0 -1 -2 PICs of log area 2 p = 0.34 p=0.36 -500 0 500 PICs of toughness 1000 18
    19. 19. Discussion • Prediction 1 (Hemiepiphytic figs ~ low leaf area and SLA) – Not supported – Environmental factors drive reported leaf variation (e.g. Holbrook & Putz 1996) – Hemiepiphytes may have evolved other mechanisms to deal with water stress 19
    20. 20. Discussion • Prediction 2 (Leaf area ~ lamina toughness) – Not supported – Veins and petioles may be sufficient to support large leaves. • Prediction 3 (Leaf area ~ lamina toughness across phylogeny) – Not supported – Evolution of leaf size and toughness not correlated across the phylogeny 20
    21. 21. Discussion: Limitations • Sampling intensity may not have accounted for intraspecific variation in leaf traits • Unbalanced data set to test Hypothesis I • Ficus phylogeny is still being developed (e.g. Yao et al. 2013), and our methods are sensitive to the phylogeny used 21
    22. 22. Future Directions • The evolutionary history of leaves is not well understood • Ficus is an ideal group to study this diversity – Morphological, distributional, and life history variation • Studies based on leaf morphology, structure, venation, and architecture (Nicotra et al., 2011) • Characterize leaf transcriptomes – Determine molecular basis for variation 22
    23. 23. Acknowledgements • AFEC Instructors and Organizers – Liu Jing-Xin, Drs. Richard Corlett, Alice Hughes, Kyle Tomlinson, Uromi Goodale, Eben Goodale, Ferry Slik – Other XTBG research groups, especially the Evolutionary Ecology, Plant Ecophysiology, and PlantAnimal Interaction groups, and Pan Bo for helping with Ficus identification • XTBG Ficus collection management staff • Numerous tutorials/guides to comparative phylogenetics in R 23
    24. 24. References • • • • • • • • • • • Cruaud, A., et al. 2012. An extreme case of plant-insect codiversification: figs and figpollinating wasps. Systematic Botany 61(6), 1029-1047 Felsenstein K. 1985. Phylogenetics and the comparative method. American Naturalist 125, 1-15.. Hao, G-Y., et al. 2010. Differentiation in leaf water flux and drought tolerance traits in hemiepiphytic and non-hemiepiphytic Ficus tree species. Functional Ecology 24(4), 731740 Harrison, R.D. 2005. Figs and the diversity of tropical rainforests. BioScience 55(12), 1053-1064. Holbrook, N.M., and Putz, F.E. 1996. From epiphyte to tree: differences in leaf structure and leaf water relations associated with the transition in growth form in eight species of hemiepiphytes. Plant, Cell and Environment 19, 631-642. Jones, C.S., et al. 2008. Leaf shape evolution in the South African genus Pelargonium L’He’R. (Geraniaceae). Evolution 63-2, 479-497 Niklas, K.J. A mechanical perspective on foliage leaf form and function. New Phytologist 143, 19-31. Nicotra, A.B., et al. The evolution and functional significance of leaf shape in the Angiosperms. Functional Plant Biology 38, 535-552 Revell, L.J. phytools: an R package for phylogenetic comparative biology (and other things). Methods in Ecology and Evolution 3(2), 217-223. Westbrook, J.W. et al. 2011. What makes a leaf tough? Patterns of correlated evolution between leaf toughness traits and demographic rates among 197 shade tolerant woody species in a Neotropical forest. The American Naturalist 177(6), 800-811. Yao, X., et al. Exon-Primed Intron-Crossing (EPIC) Markers for Evolutionary Studies of Ficus and Other Taxa in the Fig Family (Moraceae). Appications in Plant Science 1(10). 24
    25. 25. 3 1 2 4 5 1. South China Agricultural University 3,5. Xishuangbanna Tropical Botanical Garden 25 2. University of Science, Vietnam National University 4. University of Minnesota
    26. 26. Questions? 26
    27. 27. F. auriculata F. ruficaulis F. hirta F. cyathistipula F. deltoidea F. ischnopoda F. hispida F. cyrtophylla 27

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