Pollination Biology

1
Pollination Biology

• The Coevolution of Insects and Flowering Plants

2
The Importance of Insect Pollination -1

• To insects
• bees and adult lepidopterans are entirely
  dependant on floral products for food
• bees occupy a low trophic level (herbivores) and
  thus there is abundant energy to support large
  populations

3
The Importance of Insect Pollination - 2

• To plants
• of great significance to both cultivated and
  non-cultivated plants many plants would become
  extinct without pollinators due to coevolutionary
  dependance

4
The Importance of Insect Pollination - 3

• To humans
• Direct impact - about 1/3rd. of our diet comes
  directly from plants (fruits, vegetables, nuts)
  or by
• Indirect impact (alfalfa, clover ? animals) that
  we consume

5
Steps in the Evolutionary Process of Pollination
6
1- Pollination in Gymnosperms

• All gymnosperms are wind pollinated
• Male and female cones lie far apart from one
  another even if they are on the same tree
• Great wastage of plant pollen (male)
• Why is wind pollination a successful strategy for
  gymnosperms?

7
Gymnosperms or Conifers
Male and Female Cones are Far Apart
8
Does Wind Pollination Work for Angiosperms?
9
Yes!
in plant communities where huge stands of
relatively few species occur (almost
monoculture) such as in grasslands and savannahs
10
Taiga (l) and Temperate Grassland
11
What Pollination System Would Be Most Effective
in Tropical Rain Forests?
Here, several hundred plant species may be
present in the immediate vicinity. The plants of
one species are few and far between. The biota is
much too complex to rely on wind pollination.
12
Tropical Rain Forest
13
What is needed is a magic bullet that can visit
one flower to pick up pollen and then seek and
find the next individual of that species and
carry the pollen to it.
14
Animal vectors are smart enough and agile enough
to do this.
Thus, plant species and animal species have
co-evolved to use each other to accomplish
feeding and reproductive needs
15
Pollination in Early Flowering Plants

• Use of lightweight, windborne pollen
• Early insect pollination of angiosperms
  (flowering plants) was accidental.
• Early insects were simply feeding on plants and
  bumped into anthers
• More efficient than wind however, and thus was
  selected for
• Early pollinators were very likely beetles or
  possibly flies

16
Scarab Beetles Tumbling Into Flower Head
17
Blister Beetle Pollinating Goldenrod
18
Flower Fly Receiving Pollen
19
Flower Flying Transferring Pollen
20
Pollination by a Long-Tongued Bee Fly
21
A Tachinid Fly Pollinator
22
Steps in the Evolutionary Process of Plant
Adaptations

• sticky pollen grains
• evolution of pollen as a food source
• production of floral scents (attractant odors)
  and sweet fluid (nectar) occurred and
• finally, development of flower colors and
  ultraviolet nectar guides on the petals

23
A Generalized Flower of an Angiosperm
24
Steps in the Evolutionary Process of Insect
Adaptations

• increased perception of odors and colors, over
  time, by pollinating insects
• increased ability to associate these sensory cues
  with food

25
Concept of Flower Constancy

• Defined as the degree to which a pollen forager
  restricts itself to one species of plant during
  the time that it is flowering.
• High flower constancy promotes increased
  efficiency in pollination to benefit of both
  plant and insect
• Flower constancy may influence temporal
  succession of flowering among different species
  in a given area

26
How Do Structural Plant Adaptations Facilitate
Flower Constancy?

• Nectar and pollen are plant resources
• They are usually well protected by floral parts
  (fusion of petals, etc. in a tube that surrounds
  the stamens
• Thus, a pollinator that goes from one species to
  another (i.e. has low flower constancy) will be
  less efficient because it has to figure out how
  to get into different flower types

27
A Generalized Flower of an Angiosperm
28
Concept of Degree of Pollinator Specialization

• Monolectic bees pollinate only one species of
  plant
• Oligolectic bees pollinate a number of species
  in within closely related families of plants
• Polylectic bees pollinate a wide variety of
  plant species

29
Monolectic Bees vs. Polylectic Bees

• Monolectic bees are highly specialized and
  coevolved with specific host plants ex. Andrena
  sp. pollinates Salix (willow) in early spring
• Monolectic bees are common in the tropics
• Oligolectic and polylectic bees, on the other
  hand, are generalists and are most common in
  temperate regions. Plants that they pollinate are
  likely to be receptive to other pollinating
  insects as well.

30
Dont Confuse Concepts
an oligolectic bee can have high flower
constancy but simply visits a succession of
flowering species that mature at different times
during the growing season
31
Honey Bees Are Polylectic How Do We Know This?
Because of the great variety of commercial honeys
that are available in supermarkets honey
derived from sweet clover is just one of many
that are available
32
Characteristics of Honey Bees That Make Them Good
Pollinators

• branched hairs or setae
• scopa and pollen baskets
• pollen comb and brush on leg
• proboscis
• bees can tell time, have good color vision and
  are excellent communicators

33
Are Bumble Bees Good Pollinators ?

• Yes! In terms of efficiency, they are very
  efficient pollinators
• However, due to having annual colonies rather
  than perennial ones, they are not present in
  sufficient numbers for spring-pollinated crops
• Bumble bees become very efficient in mid to late
  summer

34
Are Solitary Bees Good Pollinators?

• Yes but they also fluctuate greatly in
  population numbers

35
Comparison of Number of Alfalfa Flowers
Visited/Minute

• Honey bee 7 to 17
• Bumble bee 10 to 30
• Solitary bee 9 to 40

36
Percentage of Flowers that Were Visited that Were
Actually Pollinated

• Honey bees 2
• Bumble bees 80
• Solitary bees 95-100

Conclusions?
37
Common Pollination Strategies -1
38
Honey Bee Laden With Pollen
39
Hind Leg of Worker Bee
Pollen basket
Pollen press
Pollen comb
40
Halictid Bee and Host
41
Carpenter Bee Busy at Work!
42
Conopid Fly (Wasp Mimic) Pollinating a Berry Bush
43
Skipper/Coreopsis Coevolution
44
Swallowtail/Thistle Coevolution
45
Common Pollination Strategies - 2
46
A Sphinx-Pollinated Flower
47
Purple Trillium Produces a Carrion-Like Odor
and Is Attractive to Flies
48
Green Bottle Fly and Composite Host
49
How Plants Attract Insects - 1

• Visual Cues
• Petals or sepals with obvious size, shape and
  color
• Butterflies like red and yellow colors
• Bees prefer colors at the blue end of the
  spectrum
• Moths and bats see only white or very pale colors
• Bulls eyes, splotches and nectar guides are
  important - especially against a green background

50
How Plants Attract Insects - 2

• Olfactory cues
• Flower fragrance may vary from sweet and pungent
  to fetid (manure) odors to carrion odors

51
How Plants Attract Insects 3

• Shape Considerations must attract the vectors
  and prevent pollen and nectar robbers from
  stealing the rewards
• See next slide for examples

52
Flower Shape Insect Vector

• Flowers hang down and have long styles and
  filaments
• Easy entrance
• Landing platform, perches

• hovering insects
• heavy-bodied beetles
• Non-hovering insects and birds

53
Rewards for Good Vectors -1

• Nectar
• comes from a nectary which is connected to phloem
• a carbohydrate rich droplet but weak in trace
  vitamins and minerals
• critical for hummingbirds and butterflies
• evaporated nectar is honey

54
Rewards For Good Vectors -2

• Pollen
• A decent vegetable food contains protein,
  starch, oil and other nutrients
• Richer than nectar in vitamins and minerals
• A basic protein supply bees and beetles
• Fortunately enough sticks to the body to get
  transferred to the second flower

55
Bees vs. Wasps

• Bees feed their larvae honey which is a mixture
  of nectar and pollen
• Wasps feed their larvae meat mostly paralyzed
  arthropods
• Bees have plumose or feather-like hairs
• Wasps have unbranched hairs like we do
• Bees evolved from hunting wasps (Sphecoidea)

56
Solitary Bees

• Over 20,000 known species of bees known and
  greatest portion by far are solitary
• A solitary bee is a female that provisions and
  lays an egg in a cell in a nest by herself.
• A continuum from solitary to eusociality as we
  have previously discussed

57
A Solitary Eumenid Bee Pollinating Goldenrod
58
Lots of Speciation in the Genus Andrena (Family
Andrenidae)!
59
Closeup of Andrenid Bee
60
Andrenid Bee Nesting Site
61
Communal Nesting

• Nests are built individually, but many nests may
  occupy a small area due to local conditions (soil
  type, etc.)

exposed, sandy area
forest litter
62
How Pheromones Are Involved

• Bring the two sexes together prior to mating
• In some species, males will mark the female with
  a pheromone after mating -- that makes her
  unattractive to other males

63
END