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Plants And Pollination Biology


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Plants And Pollination Biology

  1. 1. J.D. Lewis Fordham University Plants and pollination biology (what’s a nice plant like you doing in a place like this?)
  2. 2. The importance of flowers <ul><li>Flowers evolved relatively recently, yet ~ 80% of all plant species are flowering plants </li></ul><ul><ul><li>e.g, of the > 4600 plant species in the NE US, roughly 4000 are flowering plants </li></ul></ul><ul><li>The rapid diversification of flowering plants suggests that pollination is a key, if not the key, factor limiting plant populations </li></ul>
  3. 3. Reproduction in plants <ul><li>Plants may reproduce sexually or asexually </li></ul><ul><li>Most asexual reproduction in plants involves vegetative structures </li></ul><ul><li>Agamospermy : asexual production of seeds </li></ul><ul><ul><li>is found in a variety of species </li></ul></ul><ul><ul><li>generally results in clones </li></ul></ul>
  4. 4. Sexual reproduction <ul><li>Sexual reproduction involves the combining of two gametes, sperm cells and eggs, to form a new zygote (embryo) </li></ul>
  5. 5. Floral structure <ul><li>Pollen grains are produced in the anthers , part of the stamen , and carry sperm cells </li></ul><ul><li>Eggs are produced in the ovary , which is part of the carpel </li></ul>
  6. 6. Floral structure <ul><li>In addition to anthers and carpels, flowers typically have petals and sepals </li></ul>
  7. 7. The parts of a flower <ul><li>Calyx : the sepals collectively </li></ul><ul><li>Corolla : the petals collectively </li></ul><ul><li>Perianth : the calyx and corolla collectively </li></ul><ul><li>Androecium : the stamens collectively </li></ul><ul><li>Gynoecium : the carpels collectively </li></ul>
  8. 8. Arrangement of flower parts <ul><li>Parts may be in spirals along an elongated receptacle or may be in whorls </li></ul><ul><li>Floral parts of same whorl may be fused, and parts of different whorl(s) may be fused </li></ul><ul><li>Ovary position may not always be at the base of the flower </li></ul>
  9. 9. Variations in flower structure <ul><li>Regular : flowers that are radially symmetrical </li></ul><ul><ul><li>parts of whorl are similar in shape and radiate from the center of the flower </li></ul></ul><ul><ul><li>color patterns may be irregular </li></ul></ul><ul><li>Irregular (zygomorphic): flowers that are bilaterally symmetrical </li></ul><ul><ul><li>e.g., snapdragons </li></ul></ul>
  10. 10. Inflorescences <ul><li>Arrangement of flowers in aggregations </li></ul><ul><li>Is another key aspect of pollination ecology </li></ul><ul><ul><li>Aggregations of flowers may increase the attractiveness to pollinators </li></ul></ul><ul><ul><li>The form of the inflorescence may affect the behavior of pollinators </li></ul></ul>
  11. 16. Flower form and pollination <ul><li>Pollen transfer usually occurs by wind, water or animals </li></ul><ul><li>Flower form generally reflects the mode of pollen dispersal </li></ul><ul><ul><li>Animal-pollinated flowers are showy; wind-pollinated flowers are not </li></ul></ul><ul><ul><li>Evolutionarily, showy flowers may be a disadvantage in wind-pollinated plants </li></ul></ul>
  12. 17. Wind pollination <ul><li>No need to produce showy flowers, scents or nectar </li></ul><ul><li>Anthers and stigmas are well-exposed </li></ul><ul><li>Males and females are separated on the same plant </li></ul><ul><li>Plants often grow in dense clusters </li></ul>
  13. 18. Aquatic plants <ul><li>Plants in 31 genera of 11 families produce flowers underwater </li></ul><ul><li>Aquatic plants often produce large pollen that moves on the surface of the water </li></ul><ul><ul><li>pollen often is sticky and forms rafts </li></ul></ul><ul><li>In some marine species, pollen release coincides with low tide </li></ul><ul><li>Stigmas often are modified for pollen contact </li></ul>
  14. 19. Visual displays <ul><li>Animal-pollinated plants coevolved with their pollinators </li></ul><ul><li>Selection favored floral modifications that promoted consistency in pollinator type </li></ul><ul><li>Beetles and flies likely were among the earliest pollinators </li></ul><ul><li>Beetles and flies are attracted by large flowers with fruity or musty odors </li></ul>
  15. 20. Bees <ul><li>The most important group of pollinators </li></ul><ul><li>Flowers are showy, blue or yellow and brightly colored </li></ul><ul><li>Often are scented </li></ul><ul><li>Honey guides : distinctive patterns that aid recognition </li></ul><ul><ul><li>may include UV patterns </li></ul></ul><ul><li>May have landing platforms </li></ul><ul><ul><li>e.g., snapdragons </li></ul></ul>
  16. 21. Butterflies and moths <ul><li>Diurnal flowers often are similar to bee flowers, but unscented and have long, slender corollas </li></ul><ul><li>Nighttime flowers often are sweetly scented, light colored, and have a long, slender corolla </li></ul><ul><li>Butterflies can see red but have a weak sense of smell </li></ul><ul><li>Moths can detect scents </li></ul>
  17. 22. Birds and bats <ul><li>Bat flowers often are large, produce copious nectar, are dull colored and are only open at night; scents often are very strong and fruity or musty </li></ul><ul><li>Bird flowers produce copious but thin nectar, are odorless and are red or yellow </li></ul>
  18. 23. Odors and acoustic guides <ul><li>Many flowers have odors </li></ul><ul><li>Odors can attract pollinators over longer distances, but are harder to pinpoint </li></ul><ul><li>Odors can differ independently of flowers, and may attract one group but repel another </li></ul><ul><li>Some plants use acoustic guides for bats </li></ul><ul><li>Much less is known about odors and acoustic guides than about colors </li></ul>
  19. 24. Floral rewards <ul><li>The two key rewards are pollen and nectar </li></ul><ul><li>Pollen provides protein </li></ul><ul><li>Nectar provides sugar </li></ul><ul><li>Flowers may also serve as egg-laying sites </li></ul>
  20. 25. Limiting unwanted visits <ul><li>Plants limit pollinator visits so that pollen is likely to go to a plant of the same species </li></ul><ul><li>Changes in flower shape are the main way </li></ul><ul><ul><li>e.g., long tubes, spurs and small cones </li></ul></ul><ul><li>Reward type and timing are also common </li></ul><ul><li>Nonetheless, many flowers are visited by large numbers of inefficient pollinators </li></ul><ul><li>Some insects are nectar robbers </li></ul>
  21. 26. Pollination syndromes <ul><li>Color, odor, reward type and timing, and shape all influence the type of floral visitor </li></ul><ul><li>Pollination syndromes : certain combinations of traits associated with specific pollinators </li></ul><ul><li>However, the syndromes are just general patterns </li></ul><ul><li>Also, generalists may be favored under some fairly broad conditions </li></ul>
  22. 27. Mating systems <ul><li>Mating systems refers to biological factors that determine who mates with whom </li></ul><ul><li>Some species can self-fertilize </li></ul><ul><li>Others are obligate out-crossers </li></ul><ul><li>Some are a combination </li></ul><ul><li>Inbreeding often has fitness costs, so there is selection for outcrossing in many species </li></ul><ul><li>Outcrossing often is enhanced by negative assortative mating </li></ul>
  23. 28. Assortative mating <ul><li>Plants with similar phenotypes are more likely to mate with one another </li></ul><ul><li>Negative assortative mating - individuals that tend to mate with dissimilar phenotypes </li></ul><ul><ul><li>Causes obligate outcrossing </li></ul></ul><ul><ul><li>The two primary forms are heterostyly and self-incompatibility </li></ul></ul>
  24. 29. Self-incompatibility <ul><li>There are two general types of systems </li></ul><ul><li>G ametophytic SI - haploid pollen carries an allele shared by diploid stigma </li></ul><ul><li>Sporophytic SI - diploid pollen parent carries an allele shared by diploid stigma </li></ul><ul><ul><li>Sporophytic SI is more restrictive </li></ul></ul>
  25. 30. Self-compatibility <ul><li>May be favored where a particular genotype is successful in a particular location </li></ul><ul><li>Cleistogamous flowers may partly be explained by this, but the data are equivocal </li></ul><ul><ul><li>Flowers that open are chasmogamous </li></ul></ul><ul><li>Pollen to ovule ratio is often much lower in self-compatible species </li></ul>
  26. 31. Plant gender <ul><li>Cosexual plants - function as both males and females simultaneously </li></ul><ul><li>Perfect flowers - hermaphroditism </li></ul><ul><li>Monoecy - separate male and female flowers on the same plant </li></ul><ul><li>Dioecy - male and female flowers on separate plants </li></ul>
  27. 32. Plant gender (cont.) <ul><li>These three systems can exist in combination </li></ul><ul><li>Gynomonoecy (andromonoecy is more common) </li></ul><ul><li>Andromonoecy </li></ul><ul><li>Gynodioecy </li></ul><ul><li>Androdioecy (gynodioecy is more common) </li></ul><ul><li>Sequential hermaphroditism - flower usually begins as male </li></ul>
  28. 33. The genetics of plant gender <ul><li>Cosexuals may self-fertilize, or not </li></ul><ul><li>Perfect flowers can function as if they were unisexual ( Cryptic dioecy ) </li></ul><ul><li>Fitness maximization is thought to drive variation in the ratio of female to male function </li></ul>
  29. 34. Pollen competition <ul><li>Most plants have more ovules than ever produce seeds </li></ul><ul><li>Extra ovules may exist for three reasons </li></ul><ul><ul><li>Pollen is limiting </li></ul></ul><ul><ul><li>Flowers have another function </li></ul></ul><ul><ul><li>The plant is bet-hedging </li></ul></ul>
  30. 35. Sexual selection <ul><li>Competition for pollinators within a species is analogous to competition for mates </li></ul><ul><li>Variation in pollination success may be one driver of sexual selection </li></ul><ul><li>Pollen donors may compete through visual displays (male-male competition) </li></ul><ul><li>Competition between pollen grains may be regulated by the style (female choice) </li></ul>
  31. 36. Pollen dispersal <ul><li>Pollen typically does not move very far </li></ul><ul><li>Inbreeding is common in many populations </li></ul><ul><ul><li>Most matings occur between neighbors </li></ul></ul>
  32. 37. <ul><li>In animal-pollinated species, plants are clumped, animals usually focus on patches, and most pollen ends up on the next visited flower </li></ul>Animal dispersal
  33. 38. Wind dispersal <ul><li>Wind moves pollen in short bursts, plants occur in dense stands, and pollen may be clumped and mostly released near the ground </li></ul>