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Transcript
Evolution of Plants David Baum Game plan • What are “plants” and how did they evolve? • Differences between plant and animal evolution • Some stories of plant evolution What are the three most important* events in the evolution of life on earth? 1. Oxygenic photosynthesis (cyanobacteria) 2. Invasion of land (plants) 3. Human agriculture and technology *Profoundly affecting the globe’s chemistry and ecology Early land plants were low to the ground Over-time became larger, more complex, and acquired a vascular system Time Streptophytes Angiosperms (300,000) Gnetales (80) Conifers (650) Ginkgo (1) “pteridophytes” Cycads (290) Elkinsia† Aneurophytes† Archaeopteris† Ferns, Horsetails (10,500) “bryophytes” Lycophytes (1,200) Aglaophyton† Hornworts (240) Mosses (10,000) “green algae” Liverworts (8,000) Charales Coleochaetales Chlorophytes Multiple origins of “trees” “gymnosperms” Spermatophytes Lignophytes Euphyllophytes Tracheophytes Polysporangiophytes Stomatophytes Embryophytes Crane and Leslie (2014) Why? http://www.earthhistory.org.uk/recolonisation/vegetation-in-devonian An evolutionary arm’s race • The Red Queen principle Now, here, I see it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that! (Through the Looking Glass, Lewis Carroll) Competition for light (and other resources) is a very important driver of plant evolution Problems that plants faced • Gain light, water, nutrients • Escaping predators (once animals invaded land) • Sex! If you want to know more: Botany 130, 300, 305, 401, 500 Fern sperm cell Are there differences between plant and animal evolution? • Very few – plants are excellent “model systems” • But.. – Greater diversity in sexual systems • Abundant asexuality • Self-incompatibility • Sexual system diversity Self-pollination is important in some species • Reproductive assurance Arabidopsis (pollen shed onto Hibiscus (active selfing; stigma) Ruan et al. 2010) Viola (Some flowers self in bud) Some species produce seeds asexually • May still require (self) pollen Dandelion - Taraxacum Blackberry- Rubus Mechanisms that promote cross-pollination • Spatial separation of anthers and stigma in a flower Wild buckwheat Mechanisms that promote cross-pollination • Spatial separation of anthers and stigma in a flower • Temporal separation of pollen release and stigma receptivity Male phase Aeonium Female phase Mechanisms that promote cross-pollination • Spatial separation of anthers and stigma in a flower • Temporal separation of pollen release and stigma receptivity • Self-incompatibility (SI) Mechanisms that promote cross-pollination • Spatial separation of anthers and stigma in a flower • Temporal separation of pollen release and stigma receptivity • Self-incompatibility Self pollen Cross pollen Tsuchimatsu et al. (2010) Nature Mechanisms that promote cross-pollination • Spatial separation of anthers and stigma in a flower • Temporal separation of pollen release and stigma receptivity • Self-incompatibility • Dioecy Salix (Willow) Actually it is more complicated • Gynodioecy: Females + hermaphrodites Wild strawberry • Androdioecy: Males (top) + hermaphrodites Datisca http://raven.iab.ala datiscaPics.html Consequences • SI taxa speciate slower than SC taxa • But they also go extinct slower • SI has higher net rate of diversification Emma E. Goldberg et al. Science 2010;330:493-495 Are there differences between plant and animal evolution? • Very few – plants are excellent “model systems” • But.. Hops – Greater diversity in sexual systems – More chemistry less behavior Natural rubber Opium Poppy Coffee Are there differences between plant and animal evolution? • Very few – plants are excellent “model systems” • But.. – Greater diversity in sexual systems – More chemistry less behavior – Polyploidy more common Chester et al. 2010. Genes 1(2), 166-192. Are there differences between plant and animal evolution? • Very few – plants are excellent “model systems” • But.. – – – – Greater diversity in sexual systems More chemistry less behavior Polyploidy more common More evolution by “hopeful monsters” (maybe) Examples of “hopeful monsters?” Rudall PJ, Bateman RM. 2003. Trends Plant Sci. 8(2):76-82. Rudall PJ, Bateman RM. 2002. Biol Rev Camb Philos Soc.77(3):403-441 Are flowers monsters? Pollen cone Living gymnosperms have unisexual cones Seed cone Are flowers monsters? Megasporophyll Microsporophyll (stamen) A flower is a bisexual “cone” (although unisexual flowers have evolved in many groups) If so: quite successful! • ~300,000 species of flowering plants • Dominate all land ecosystems (and several aquatic ones) • Provide all food resources for humans Pollination Stories Pollination • Pollination is transfer of pollen from anthers to stigma • Pollination ≠ fertilization • Necessary to make seeds Apple – critical for reproduction – important for agriculture Pollination (only occurs in seed plants) avoids the need for motile sperm • Pollen is a minute male plant • Can be carried by wind (rarely water) • More commonly animals do it – Insects – Birds – Mammals Pollen needs to deliver the gametes to the egg cells Stigma Pollen tubes grow through plant tissues – navigated chemically Pollen tubes grow through plant tissues – navigated chemically Plants have evolved diverse ways to get pollen from one flower to another • Wind • Water (rare) • Animals – Mutualistic (give a reward) – Parasitic (trick the animal) • Plant evolution is similar to other multicellular eukaryotes • But they are a great model for studying evolution (e.g., the evolution of sex) • Coevolution with animals for pollination (and dispersal) is important • Botany is cool Feel free to contact me: [email protected]