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