POLLINATION AND SEED DISPERSAL

Introduction

    Spring is time of rapid change

    NOW:

    • near end of leafing out
    • middle of flowering
    • entering into seed development for some

    Appropriate Time to Discuss Pollination and Seed Dispersal

    Important Roles: movement of plants, mixing of genes

     

Pollination

Definition: movement of male sex cell to female reproductive organ (differs from fertilization)

Occurs in both Gymnosperms and Angiosperms, but structures differ (cones versus flowers)

Two types of pollination are most important:

1. Wind

    examples-

      • Angiosperms: We often don’t even recognize that wind pollinated flowers are flowers because they are highly modified from flowers familiar to us. Aments (inflorescence modified for wind dispersal—no petals, big anthers, big stigmatic surfaces)
      • Gymnosperms: male cones of Pinaceae (big pollen sacs)
    • 2. Animals (primarily insects)
      • Gymnosperms: none that I know of
      • Angiosperms: animals were a major force in evolution of flower characteristics

       

      Major evolutionary trends in flowers:

    Flower evolved from shoots—leaves modified into different flower parts

Primitive flowers

  • many parts
  • unfused parts
  • radial symmetry

Advanced flowers

  • fewer # of parts
  • fusion of parts
  • attractants, guides and rewards
  • aroma, size and color (including rotting meat)
  • marking on petals to direct insects (honey guides)
  • nectar and pollen
  • bilateral symmetry
  • forces movement of insect through flower
  • inflorescence (including "division of labor")
  • greater efficiency—more reproductive parts/area
  • Pollination Ecology
  • A. Pollination Vectors
  • 1. Bees
  • a. Nectar of flower their chief source of nourishment
  • b. Prefer blue and yellow flowers
  • c. Honey guides
  • • lines on flower petals that lead bees to the nectar
  • d. Ultraviolet patterns on flowers visible to bees
  • 2. Beetles
  • a. Flowers generally white or dull in color
  • b. Strong yeasty, spicy, or fruity odors
  • 3. Flies
  • a. Flowers dull red or brown
  • b. Foul odors
  • c. Flowers called "carrion flowers"
  • 4. Moths and Butterflies
  • a. White or yellow in color
  • b. Sweet fragrances
  • 5. Birds
  • a. Flowers bright red or yellow and large inflorescences
  • b. Produce copious quantities of nectar in long floral tubes
  • 6. Bats
  • a. Generally tropical flowers that open at night
  • b. Large flowers or ball-like inflorescences
  • B. Orchid Flowers and Their Adaptations for Pollination
  • 1. Pollen grains produced in little sacs called pollinia
  • 2. Pollinia either stick to the insect pollinator or are forcibly "slapped" on the insect by a trigger mechanism
  • 3. Petals modified to resemble female wasp or bee
  • • male insects attempt to mate with flower and pick up pollinia in the process

  •  

    SEEDS AND FRUITS

    • We’ve discussed seeds and fruits before (Species descriptions, discussion of life history strategies
    • Today we will discuss characteristics in more detail, with real examples

    SEEDS-- completely matured and modified ovule containing an embryo

    Structure

    Functions
    • food material
    • germination
    • embryo
    • dispersal
    • seed coat
    • dormancy
    • protection from predation

    FRUITS—Mature ovary containing seeds

    Structure

    Functions
    • mature ovary wall
    • protection from predation
    • accessory tissue
    • dispersal

     

     

    PROTECTION:

    Morphological defenses: Structures that defend

    • spines of pine cones
    • large burs of chestnut
    • very dense pubescence

    Chemical defenses: toxic chemicals in seed coats, food material, or embryo

    • pea family
    • horse chestnut
    • Ginkgo biloba
    • tanins in oaks
    • immature fruit: sour, bitter

    Animal body guards: animals fight off predators

    e.g., ants defend some legumes

    Plant rewards ants with nectar (at base of fruit) and ants attack flies trying to lay eggs in fruit. Plant also supplies proteins/fats and lodging to ants.

    Escape in time

    predator satiation

     

    DISPERSAL

    Balistic—explosive release

    • scotch broom
    • dwarf mistletoe

    Wind

    • very small seeds (Salix, Populus, Liquidambar—fruits are capsules here)
    • hairs, plumes (Salix, Populus, Platanus)
    • wings

    samaras: Acer, Liriodendron,

    winged seeds: most Gymnosperms, Liquidambar

    • plant swaying: poppies
    • plant dispersed: tumble weeds

    Water

    • coconut

    Animals

    unintentional carrying

    • burs, barbs
    • stickum—dwarf mistletoe

    harvesting and caching

    • birds: jays, nutcrackers, passenger pigeons

      carry 70-100 seeds 10s of miles
      several pines (e.g. white bark pines, pinyon pines [pine nuts], Pinus pumila)

    • mammals: squirrels
    • big seeds: Aesculus, Quercus, Juglans, Carya, Fagus, Castanea
    • predator satiation

    eating

    • seed enclosed or attached to a edible material (food is reward for consumer)
    • fate of seed: (note: need to lighten balast)
      • discarded (we do that)-- fastest
      • regurgitated
      • passed through gut—slowest
    • characteristics of fruit
    • prominent display position
    • prominent color when ripe
    • protection

      green when immature
      bitter when immature

       

    • high energy cost to produce