Transcript Lecture PPT - Carol Lee Lab

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]