Evolution of Plant Biodiversity

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Evolution of Plant Biodiversity
Gymnosperms dominate
Seedless vascular plants
of families
First gymnosperms
Mackenzie 2003
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Phylum Anthophyta, Angiosperms (Flowering
plants) 250,000 species named to date
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Key Angiosperm featuresAngion container,
sperm seed
Advanced transport tissues tracheids vessels
in xylem tissue, wide channels for
moving water Flowers
pollination syndromes more efficient
reproduction deliver your pollen to eggs of
your own species Protected seeds inside fruit
provides means of dispersal for offspring, via
animals that eat fruit, or wind, or water
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Key Angiosperm featuresAngion container,
sperm seed
Advanced transport tissues tracheids vessels
in xylem tissue, wide channels for
moving water tracheids have
an extra, outer cell wall re-inforced with
lignin, a super-strong material that allows
stems of plants to stand upright - there are
holes in the lignin wall to allow water to flow
from one to the next - cells are dead by the
time they function in water transport - wood is
basically just lots of tracheids pressed together
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Tracheids and vessel elements
Gymnosperm xylem tissue contains only
tracheids Angiosperm xylem contains both
tracheids and vessel elements Tracheids
elongated single cells that transport water in
the xylem tissue - pass water
cell-to-cell Vessel elements wider vessels
?
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Tracheids and vessel elements
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Understand the progressive adaptations to life on
dry land that culminated in the
super-successful angiosperms
p. 639
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Reproductive structures of seed plants
Gymnosperms Angiosperms
Flower
Pistil/Carpel(s)
Stamen
Petal
Sepal
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Tip of stamen is the anther, which contains the
microsporangia produce microspores grow
into pollen grains, housing male
gametophyte (only 2 cells big!)
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Anther releasing pollen grains (after meiosis)
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Base of carpel ovary, protective structure that
contains ovules the megaspore inside each
ovule grows into the female gametophyte 1 egg
nucleus 2 polar nuclei, which will become the
endosperm
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Double Fertilization
Pollen grain has 2 cells 1 grows into pollen
tube, penetrates ovary other 1 forms 2
sperm sperm 1 fertilizes egg sperm 2
fuses with both polar nuclei to form the
endosperm (3N, triploid) Endosperm becomes
food for the growing embryo
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Double Fertilization
Each ovule is initially surrounded by two
integuments After fertilization, these become
the hardened seed coat The whole ovary wall
then thickens into the pericarp, the thick
outer wall of the fruit
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Ovule becomes seed, ovary becomes fruit
Campbell Reece 2002
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Angiosperm seeds arent exposed like naked
gymnosperm seeds Instead, they are protected
by a ripened ovary wall (pericarp),
sometimes with additional accessory
parts like the outer tissue of this apple
Stern 1991
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Pollination syndromes
Co-evolution between angiosperms and their animal
pollinators - animal gets a reward of sugary
nectar (energy-rich) - plant attaches or
dusts animal with pollen, which will then be
transferred to the next flower Termed
co-evolution because changes in one partner
trigger compensating changes in the other
- for example
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This flower has a mechanism causing stamens to
arch over and dust the back of a honeybee with
pollen
Plants pollinated by nocturnal animals (moths,
bats) have flowers that bloom at night
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Many flowers are distinctively shaped so only
a co-evolved pollinator has the right length
appendage to reach in, get the nectar reward
Hummingbird pollinated flowers are usually red
with long tubes
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Some flowers have patterns in ultraviolet part of
light spectrum - invisible to us but clear to
insect eyes can form landing strips
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Seed dispersal
wind-dispersed seeds are fluffy or have
wings to increase drag
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Fruit dispersal
burrs dry fruit with hooks to stick to animals
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Fruit dispersal
Most plants invest lots of energy in their fruit
for one reason ? This disperses the
offspring of the plant, as the animal eventually
poops out the undigested seeds somewhere else
The seeds of many plants cannot develop until
they have passed through an animals digestive
system! ?
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vascular plants
p. 648 of Freeman 3rd ed.
Gymnosperms
angiosperms
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Carnivorous plants
A source of nitrogen is essential for cells to
make proteins - usually nitrate, the
water-soluble compound NO3-2
Plants that live in nutrient-poor, swampy
conditions may be unable to get nitrogen from
the soil through their roots Some therefore
capture and digest insects as a source of
nitrogen Venus flytrap swings closed when 2 of 3
trigger hairs are bent by an insect Other
plants drown insects in contained water or
catch them on sticky leaves
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Parasitic angiosperms
Cuscuta sp. (dodder)
Monotropa sp.
Non-photosynthetic parasitize other plants to
obtain nutrition
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Plant Chemistry
Because plants cant move, many produce toxic
chemicals to protect themselves from herbivorous
animals and competitors - many plants leach
chemicals out into the surrounding soil to
inhibit growth of competitors (termed
allelopathy) - others produce toxins such as
caffeine nicotine, to deter herbivorous
animals from eating their leaves Humans use
plant chemicals as medicinal or recreational
drugs - 25 of modern medicines involve the
plant products - co-evolved insect herbivores
can tolerate chemical defenses of their
particular host plant, leading to host
specialization
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Plant Revenge
Plants can tell when a caterpillar is eating
them, by recognizing its spit Plants may
release airborne chemicals that attract wasps,
which come and sting the caterpillar The wasps
paralyze the caterpillar and lay their eggs
inside it ? wasp larvae eat the living
but paralyzed caterpillar from the inside
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Plant-insect Coevolution Biodiversity
Most species on earth, by the numbers, are
herbivorous insects - more than 135,000
species of beetles feed on flowering
plants Studies suggest that when angiosperms
started speciating, beetles that fed on them also
divided into specialist populations, which each
evolved into new beetle species Coevolution can
promote species formation - when one plant
evolves into two different species, so do its
parasites, predators and pollinators!
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Plant-insect Coevolution Biodiversity
Consider what happens when an ancestral plant
undergoes speciation and evolves into two
distinct plant species...
mountains
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Plant-insect Coevolution Biodiversity
Consider what happens when an ancestral plant
undergoes speciation and evolves into two
distinct plant species...
Rain forest species
Desert species
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Plant-insect Coevolution Biodiversity
But what happens to the pollinators (say,
butterflies) and herbivores (beetles) that were
symbionts of that ancestral plant...?
herbivore (beetle)
pollinator (butterfly)
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Plant-insect Coevolution Biodiversity
But what happens to the pollinators (say,
butterflies) and herbivores (beetles) that were
symbionts of that ancestral plant...?
Rain forest species
Desert species
Pollinators and herbivores also form new species
when their host plant speciates coevolution
promotes formation of many new species
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Human Dependency on Angiosperms
Crucial to the global carbon cycle Critical
habitat for animals (including us) Our economy
is dependent upon angiosperms (ecosystem
functions) Sources of everyday products (e.g.
hardwoods, medicines) Source of our food
(directly or indirectly) over 80 of our food
comes from only six species rice, soy,
wheat, corn, sorghum, and millet