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 More chemistry less behavior Maybe more evolution by “hopeful monsters”

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

Are there differences between plant and animal evolution? Very few – plants are excellent “model systems” But.. Greater diversity in sexual systems Abundant asexuality More chemistry less behavior Maybe more evolution by “hopeful monsters” Polyploidy

Why is polyploidy common in plants? Tolerance of different ploidy levels during development (dosage compensation?) Often make unreduced gametes (“rescues” meiotic problems) Chester et al. 2010. Genes 1(2), 166-192.

Why is polyploidy common in plants? Tolerance of different ploidy levels during development (dosage compensation?) Often make unreduced gametes (“rescues” meiotic problems) http://www.amjbot.org/content/95/6/713/F1.large.jpg

Why is polyploidy common in plants? Tolerance of different ploidy levels during development (dosage compensation?) Often make unreduced gametes (“rescues” meiotic problems) Many crops are polyploid wheat and potato http://www.amjbot.org/content/95/6/713/F1.large.jpg

Polyploidy – Whole Genome Duplications Very many instances in land plant evolution All land plants are ancient polyploids Plants have lots of “extra” genes

Polyploidy – Whole Genome Duplications Very many instances in land plant evolution All land plants are ancient polyploids Plants have lots of “extra” genes Sometimes polyploidy is associated with speciation Allopolyploidy Hybrid speciation D. Soltis and P. Soltis: Am. J. Bot

Pollination Stories

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)

How do you think this evolved? What else would you like to know?

At the other extreme: Figs and fig wasps figs are “tomb blossoms”

Implications There is a one-to-one relationship between a fig species and its wasp pollinator species Predicts cospeciation: that the figs and wasp

Prediction: One-to-one species association Cospeciation A a C c B b D Wasp phylogeny Fig phylogeny C c B b D d E e F f

Actual result Host switching Weiblen and Bush (2002)

Desert Ecology and Evolutionary Biology Botany 575 • Tom Givnish and Kate McCulloh Weekly meetings in Spring 2016 / field trip March 19 – 27, 2016 Deserts are extreme environments that support an unexpected diversity of plant species and adaptations. An historic opportunity to study speciation and photosynthetic/hydraulic adaptations in desert plants, especially winter annuals, is likely this year due to a massive El Niño. We will visit a wide range of desert habitats and conduct research during a 8-day field trip to southern California this spring, complemented by lab work and writing papers for publication. • Open to undergrads and grad students • Meets 1:00 – 2:15 W • Costs ca. $675/student • Applications due December 1 – http://botany.wisc.edu/Botany-575

Feel free to contact me: dbaum@wisc.edu Plant evolution is similar to other multicellular eukaryotes Arm’s race for light Polyploidy is especially important Coevolution with animals for pollination (and dispersal) is important Botany is REALLY important Feel free to contact me: dbaum@wisc.edu

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