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Chapter 24-Flowering Plant and Animal Coevolution
coevolutionary plant-animal associations
– alliances that have influenced the evoluton
of both partners.
These examples show that plants have acquired
traits that are attractive to particular animals, and the
animals’ behavior has evolved in ways that benefit
plants.
-Fleshy fruits are evolutionary products of
plant-animal dispersal relationships.
Flowering plant-animal coevolution interactions
are important in agriculture
The production of
crops such as
apples, cherries, and
other fruits rely on
bee pollinators.
Co-evolution is important in global ecology
The continued existence of most flowering plants
depends on appropriate pollinators or dispersal
agents.
Some plants rely on only a single species of
pollinator or dispersal agent.
Some plants rely on only a single species of
pollinator or dispersal agent.
If the population of a single pollinator or dispersal
agent declines or becomes extinct:
-the plants are more vulnerable to
extinction
Some plants rely on only a single species of
pollinator or dispersal agent.
If the population of a single pollinator or dispersal
agent declines or becomes extinct:
-the plants are more vulnerable to
extinction
-the population of any animals that rely on
the plants for food may also decrease or
become extinct.
Ex: Brighamia, a Hawaiian flowering plant
This plant has stopped reproducing naturally
because the specific pollinator has become
extinct.
It is important to understand the processes of pollination,
dispersal, and coevolutionary interactions for:
It is important to understand the processes of pollination,
dispersal, and coevolutionary interactions for:
-preservation of endangered plant and animal species
-restoration of damaged or altered habitats
-maintaining global biodiversity
Pollination
If pollination is accomplished and pollen and stigma
are compatible, a pollen grain will germinate to
form a pollen tube.
The sperm cells are then transported to egg cells
within ovules in the ovary.
Pollination
The flower is an adaptation that increases the
efficiency of pollination.
Most angiosperms produce bisexual flowers.
Most angiosperms produce bisexual flowers.
Bisexual flowers are comprised of:
-pollen-producing stamens
-ovule-containing carpels.
Bisexual flowers are both common and ancient.
The oldest living groups of flowering plants
(Amborella and some water lilies) have bisexual
flowers.
Some plants are self-fertile, and capable of self-
pollination and self-fertilization.
Reproductive strategies
Reproductive strategies
Self-pollination (selfing) occurs when pollen is
transferred to the stigma of the same plant.
Reproductive strategies
Self-pollination (selfing) occurs when pollen is
transferred to the stigma of the same plant.
Selfing results in reduced genetic diversity of the
offspring compared to cross-pollination.
Many plants are capable of selfing, including
many weedy species.
Reproductive strategies
Reproductive strategies- Self pollination
Disadvantages
• reduced genetic diversity
Advantages
• only a single plant is
required for pollination
• less energy
• low population densities
• plants that invade new or
disturbed habitats.
Some common plants generally reproduce by
selfing, including beans, peas, and tomatoes.
Reproductive strategies
A few extreme examples of self-pollinating
plants produce flowers that never open.
Almost all self-pollinating plants have flowers
that are less showy than their cross-pollinating
relatives.
Reproductive strategies
Almost all self-pollinating
plants have flowers that
are less showy than their
cross-pollinating relatives.
Reproductive strategies
Cross-pollination (outbreeding)
– mating of sperm and egg from genetically
different organisms of the same species.
Reproductive strategies
Reproductive strategies- Cross-pollination
Disadvantages
• energy expenditure
Advantages
increased genetic diversity
Many plants have mechanisms to increase the
chance of cross-pollination even though they may
be capable of self-pollination.
Reproductive strategies
The most obvious mechanism to insure cross-
pollination is the separation of the sexes into
different individuals (dioecious plants).
The willows are
dioecious, with
separate male and
female plants.
Self-pollination can be prevented (or greatly
reduced) in monoecious plants by various
factors including:
1) Different timing of production of pollen and the
receptivity of the stigma
Self-pollination can be prevented (or greatly
reduced) in monoecious plants by various
factors including:
1) Different timing of production of pollen and the
receptivity of the stigma
2) A genetic system that prevents the elongation of the
pollen tube on a stigma of the same plant (self-
incompatibility)
A flower’s own pollen can begin to grow through
the style toward the ovary.
Enzymes produced within the pollen tube destroy
pollen-tube RNA, which causes the tube to stop
growing.
Self-pollination can be prevented (or greatly
reduced) in monoecious plants by various
factors including:
1) Different timing of production of pollen and the
receptivity of the stigma
2) A genetic system that prevents the elongation of the
pollen tube on a stigma of the same plant (self-
incompatibility)
3) A genetic system that prevents genes expressed in
cells at the stigma surface allow genetically distinct
pollen from flowers of the same species, but not
genetically identical pollen
These early roadblocks prevent the formation of
unhealthy, inbred embryos, allowing eggs the
change to successfully outbreed.
A number of plants do not require pollination at
all to produce seeds.
Apomixis is the general term for this type of
reproduction, where no fusion of egg and sperm
nuclei occurs.
Although there are showy flowers produced,
pollen is not actually involved in seed production
and offspring are clones of the single parent
plant.
In many plants, pollination is affected by vectors.
A vector is some factor, either biotic or abiotic, that
transfers the pollen from one flower to another.
Different flowers have features that adapt them to
pollination by different types of vectors.
Different flowers have features that adapt them to
pollination by different types of vectors.
The set of flower and pollen traits that adapt a plant
for pollination by a particular vector is its
pollination syndrome.
This system almost always includes some kind of
reward for the vector, such as nectar or pollen.
Nectar is typically rich in sugar and pollen has high
protein content.
Flower color
Beetles, flies and bats are generally not
attracted by flower color.
Flower color
Beetles, flies and bats are generally not
attracted by flower color.
Plants pollinated by these vectors have dull
colored flowers.
Flower color
Wind pollinated flowers often lack petals.
Flower color
Visual pollinators often prefer different colors.
Flower color
Visual pollinators often prefer different colors.
Bee flowers are often blue (and generally
ultraviolet), whereas bird flowers are red or
orange.
Nectar guides
Nectar guides are generally present on bee and
butterfly flowers.
Nectar guides
Patterns on flowers act somewhat like a “bull’s
eye” guiding the pollinator to the nectar reward.
Nectar guides
In some bee flowers, the nectar guides are most
visible with UV light.
Bees can see in the UV spectrum.
Odor
Pollinators that are not attracted by colors are
usually attracted by strong odors.
Odor
Moths forage at night.
Odor
They can pick out pale or white flowers, but they
are strongly attracted to sweet odors.
Nectar and Pollen
Most biotic vectors are rewarded with nectar.
Nectar and Pollen
The nectar is usually “hidden” so that only the
vector with special structures can access the
nectar.
Nectar and Pollen
This feature is best seen in butterfly and moth
flowers, where nectar often is in deep spurs that
require a long proboscis to access.
Nasturtium
spur
Nectar and Pollen
Pollen is another reward for vectors, but the
amount varies among the flower types.
Nectar and Pollen
Beetle and bat flowers typically have the most
pollen reward.
Flower shape
Flower shape is also quite different for each type
of pollinating vector.
Beetle Flowers
Beetle flowers are typically not very colorful
and lack nectar guides and nectaries.
Beetle Flowers
The flower is regular, with a dish shape.
There is abundant pollen and numerous
stamens and pistils.
Beetle Flowers
The beetles are attracted to the flower by the
abundant pollen and can often eat significant
portions of the flower.
Fly Flowers
The main feature of fly flowers is their stench
of putrid meat.
This attracts the flies without requiring a
reward.
Fly Flowers
The largest flowers are fly flowers found in
the tropics.
Bee Flowers
Bee flowers come in many colors and
shapes, but they do not have spurs that are
found in butterfly and moth flowers.
Abundant high-sugar nectar is normal.
Butterfly and Moth Flowers
These two flower types often have
similar tubular shapes, but butterfly
flowers are adapted to the visual
foraging of butterflies and moth
flowers are adapted to the nighttime
foraging of moths.
Butterfly and Moth Flowers
These two flower types often have
similar tubular shapes, but butterfly
flowers are adapted to the visual
foraging of butterflies and moth
flowers are adapted to the nighttime
foraging of moths.
Bird Flowers
Bird flowers are often pendant (hang
downward) and tubular.
Bird Flowers
Bird flowers are often pendant (hang
downward) and tubular.
The bird vectors have long, thin
beaks to access the nectar.
Bat Flowers
Bat flowers are fairly common in the tropics.
Bat Flowers
Bat flowers are fairly common in the tropics.
Most are pendant, large flowers that open at
night.
Wind Flowers
Wind pollinated flowers are not
showy, produce massive amounts of
pollen, and have the anthers and
stigmas exserted (emergent from the
flower)
Water is also a pollen vector in a few plants.
Vallisneria male and female flowers