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Pollination

Pollination

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Pollination

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  1. Pollination

  2. Pollination • Definition: transfer of pollen from stamen to stigma • Contrast with herbivory. Animals eating plant products but: • 1) Most pollinators winged • 2) If insects, adults involved directly and not larvae • 3) Few mammals involved (except bats)

  3. The flower • Parts (see Fig. 6-1 in text)

  4. Life Cycle • Example of sporic meiosis: • Gametophytes make gametes BY MITOSIS • Zygote grows into diploid individual called sporophyte • Sporophyte makes meiospores BY MEIOSIS • Two bodies in one cycle: alternation of generations

  5. Life Cycle • Overview:

  6. Life Cycle • Overview: • Fertilization: union of sperm with egg to form zygote

  7. Floral variation • Parts may be fused • Example, petals fused to each other • Like parts fused: connation (ex., petals to petals) • Unlike parts fused: adnation (ex., stamens to petals). Snapdragon flower

  8. Floral variation • Fusing of petals can form floral tube (nectar made at bottom) • Only long-tongued pollinators can reach it. Anisacanthus (Acanthaceae) flower

  9. Floral variation • Flowers with both stamens and pistils: perfect flowers Another kind of perfection….

  10. Floral variation • Flowers with both stamens and pistils: perfect flowers • Some flowers imperfect. Either pistillate (have pistil) or staminate (have stamens). Pistillate flowers of Sagittaria Staminate flowers of Sagittaria

  11. Floral variation • Note: some species make pistillate flowers and carpellate flowers on separate individuals • This termed dioecy (MUST outcross to reproduce sexually) • Monoecy is when both sexes on same individual.

  12. Persimmon fruits Floral variation • Example of dioecious species: Persimmon (Diospyros) Pistillate flower Staminate flower

  13. Floral variation • Some flowers are missing one or more sets of basic parts: incomplete flowers • Note that all imperfect flowers are therefore incomplete!

  14. Floral variation • Floral symmetry: • Radial: can be divided into similar halves by several planes • Bilateral: can be divided into mirror images by 1 plane.

  15. Floral variation • Ovary position • Superior ovary: other parts attach below ovary (hypogynous: “hypo-” =below, “gyn-” =female)

  16. Floral variation • Example of superior ovary in a lily flower (ovary is E)

  17. Floral variation • Ovary position • Perigynous flower: ovary superior, but cup formed of fused sepals, petals, stamens around it.

  18. Floral variation • Ovary position • Inferior ovary: other parts attach above ovary (epigynous: “epi-”=above, “gyn-”=female).

  19. Floral variation • Example of inferior ovary: squash flower (this one is pistillate). Ovary

  20. Floral variation • Some flowers assembled into groups of flowers: inflorescence • Special inflorescence type: head • Example, sunflower and its relatives • Ray flowers have large fused petals (corollas fused), disk flowers small and crowded. ray flowers disk flowers

  21. Floral variation • Flowering dogwood (Cornus florida) • Inflorescence: white structures are modified leaves (bracts) that act like petals. Closeup showing individual greenish flowers Inflorescence

  22. Pollination • Why flowers so varied? Many form mutualism with animals to achieve pollination

  23. Mutualism Exceptions • Some flowering plants are wind pollinated (anemophily) • Some are water pollinated (hydrophily) Small, greenish grass flowers

  24. Pollination as Mutualism • Most flowering plants are pollinated by animals • This usually viewed as mutualism (where both species benefit) • Plant gets pollen transferred • Animal gets “reward”

  25. Rewards • Pollen: high in protein • Also has lipids, minerals, starch • Can be renewed by: • sequential anther dehiscence (multiple stamens) • poricidal anthers (buzz pollination)

  26. Rewards • Nectar: sugary fluid produced by nectar glands (nectaries) in flower • 10-60% mono- or disaccharides • May have amino acids too (butterfly flowers) • Renewable reward!

  27. Rewards • Oils/Resins: some used as construction materials, “cologne” (male solitary bee uses oil as female attractant), food for larvae (Krameria) • Edible petals (pineapple guava: New Zealand) Krameria wax gland: wasp food!

  28. Pollination • Benefits of animal pollination for plant • 1) Directed dispersal of pollen. Can get delivered from stamen to stigma with less waste • Floral cues and attractants: • Color and shape • Scent • Warmth (thermogenic plants: rare) Skunk cabbage

  29. Pollination • Benefits of animal pollination for plant • 1) Directed dispersal of pollen. • This aided by learning of floral visitors: decreases “handling time” • Fosters “floral constancy” (visiting single species on foraging trip) by bees Bumblebee visits to touch-me-not

  30. Pollination • Benefits of animal pollination for plant • 2) Style of flower as “selective racetrack” stigma style ovary 2 ovules

  31. Pollination Pollen grains • Benefits of animal pollination • 2) Style of flower as “selective racetrack” • Keep in mind that 1 pollen grain can fertilize 1 ovule • Suppose 5 pollen grains arrive on stigma stigma style ovary 2 ovules

  32. Pollination Pollen grains • Benefits of animal pollination • 2) Style of flower as “selective racetrack” • Keep in mind that 1 pollen grain can fertilize 1 ovule • Suppose 5 pollen grains arrive on stigma • Start to make pollen tubes • How many can fertilize an ovule? stigma pollen tubes style ovary 2 ovules

  33. Pollination Pollen grains • Benefits of animal pollination • 2) Style of flower as “selective racetrack” • Keep in mind that 1 pollen grain can fertilize 1 ovule • Suppose 5 pollen grains arrive on stigma • Start to make pollen tubes • How many can fertilize an ovule? • 2! First 2 to arrive! • Rest? LOSERS! stigma style ovary 2 ovules

  34. Pollination Pollen grains • Benefits of animal pollination • 2) Style of flower as “selective racetrack” • Pollen tubes are haploid (1n) • Haploid means only 1 allele (gene version) for every trait stigma style ovary 2 ovules

  35. Pollination Pollen grains • Benefits of animal pollination • 2) Style of flower as “selective racetrack” • Pollen tubes are haploid (1n) • Haploid means only 1 allele (gene version) for every trait • If an allele is recessive, then it will be expressed (can’t be masked by another, dominant allele) stigma style ovary 2 ovules

  36. Pollination Pollen grains • Benefits of animal pollination • 2) Style of flower as “selective racetrack” • Pollen tubes are haploid (1n) • Haploid means only 1 allele (gene version) for every trait • If an allele is recessive, then it will be expressed (can’t be masked by another, dominant allele) • So, fittest (fastest) pollen grains mate • Inferior genes don’t get passed to offspring. stigma style ovary 2 ovules

  37. Pollination • Style of flower as “selective racetrack” • Is there evidence that this works? • Example, Coyote melon • Gourd growing in U.S. deserts.

  38. Pollination • Style of flower as “selective racetrack” • Study done in 2000 showed that • 1) takes 900 pollen grains to fully pollinate flower • 2) 1 pollinator visit puts 650 grains/flower. By 2 hours, >4000 grains deposited on stigma • 3) Seeds produced from over-pollinated flowers produced more vigorous seedlings (compared to seeds from flowers with <900 pollen grains on stigma).

  39. Outcrossing • Major benefit of sexual reproduction: generate genetic variation • This enhanced by mating with others (outcrossing)

  40. Outcrossing • How to favor outcrossing: • 1) Dioecy Bet hedging! Some selfing can occur if no cross pollination Imperfect flowers

  41. Outcrossing • How to favor outcrossing: • 2) Floral morphology • Heterostyly: Distyly and tristyly

  42. Outcrossing Protandry • How to favor outcrossing: • 3) Floral phenology • Protandry: anthers dehisce first • Protogyny: stigma becomes receptive first

  43. Outcrossing • How to favor outcrossing: • 4) Self-incompatibility: prevents germination of self pollen or slows self pollen tube growth

  44. Pollinator Specialization • May be learned • May be species-specific • Monolecty: Flowers of 1 plant species visited • Oligolecty: Flowers of few plant species visited • Polylecty: Flowers of many plant species visited

  45. Specialization • Benefits of taxonomic specialization • Better service: can match phenology of plant/pollinator • Decrease competition (must match flower/pollinator traits) • Plant: Minimize stigma clogging with heterospecific pollen

  46. Pollination syndromes • Disclaimer: Note that we must make broad generalizations and exceptions exist to most statements!

  47. Pollination syndromes • Bee pollination: Melittophily • Bees: • intelligent, agile • visual animals: good eyesight (including UV light) • good smellers (good sense of smell) • day-active

  48. Pollination syndromes • Bee pollination • Bee pollinated flowers: • Colorful (usually not red) • Landing platform: place where bee can land on flower • Mildly fragrant. • Nectar guides: patterns of lines or dots that can guide bee to reward • Sometimes these only visible in UV light (which bees see). Petals in visible light (left) and UV (rt)

  49. Pollination syndromes • Fremontodendron decumbens (endangered chaparral shrub) flowers • UV reflectance photo (right)

  50. Pollination syndromes • Beetle pollination: Cantharophily • Beetles are: • Clumsy • Have poor vision • Dumb(er) • Active during the day (many flower-visiting ones).