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
– More chemistry less behavior
– Maybe more evolution by “hopeful monsters”
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
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
Fig phylogeny
C
c
B
b
D
d
E
e
F
f
Wasp phylogeny
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
• 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
Twentieth Century Fox