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 What are the three most important* events in the evolution of life on earth? Oxygenic photosynthesis (cyanobacteria) Invasion of land (plants) 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

Multiple origins of “trees” 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 Viola (Some flowers self in bud) Arabidopsis (pollen shed onto stigma) Hibiscus (active selfing; Ruan et al. 2010)

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 Female phase Male phase Aeonium

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 Androdioecy: Males (top) + hermaphrodites Wild strawberry Datisca http://raven.iab.alaska.edu/~dewolf/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.. Greater diversity in sexual systems More chemistry less behavior Opium Poppy Hops Coffee Natural rubber

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. Rudall PJ, Bateman RM. 2002. Trends Plant Sci. 8(2):76-82. Biol Rev Camb Philos Soc.77(3):403-441

Living gymnosperms have unisexual cones Are flowers monsters? Living gymnosperms have unisexual cones Seed cone Pollen cone

Are flowers monsters? A flower is a bisexual “cone” 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 critical for reproduction important for agriculture Apple

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)

Feel free to contact me: dbaum@wisc.edu 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: dbaum@wisc.edu