Download Pollination Pollination • Definition: transfer of pollen from stamen to

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Pollination
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)
The flower
• Parts (see Fig. 6-1 in text)
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
Life Cycle
• Overview:
Life Cycle
• Overview:
• Fertilization: union of sperm with egg to form zygote
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).
Floral variation
• Fusing of petals can form floral tube (nectar made at bottom)
• Only long-tongued pollinators can reach it.
Floral variation
• Flowers with both stamens and pistils: perfect flowers
Floral variation
• Flowers with both stamens and pistils: perfect flowers
• Some flowers imperfect. Either pistillate (have pistil) or
staminate (have stamens).
Floral variation
• Note: some species make pistillate flowers and carpellate
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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.
Floral variation
• Example of dioecious species: Persimmon (Diospyros)
Floral variation
• Some flowers are missing one or more sets of basic parts:
incomplete flowers
• Note that all imperfect flowers are therefore incomplete!
Floral variation
• Floral symmetry:
• Radial: can be divided into similar halves by several planes
• Bilateral: can be divided into mirror images by 1 plane.
Floral variation
• Ovary position
• Superior ovary: other parts attach below ovary (hypogynous:
“hypo-” =below, “gyn-” =female)
Floral variation
• Example of superior ovary in a lily flower (ovary is E)
Floral variation
• Ovary position
• Perigynous flower: ovary superior, but cup formed of fused
sepals, petals, stamens around it.
Floral variation
• Ovary position
• Inferior ovary: other parts attach above ovary (epigynous:
“epi-”=above, “gyn-”=female).
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Floral variation
• Example of inferior ovary: squash flower (this one is pistillate).
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Floral variation
• Some flowers assembled into groups of flowers: inflorescence
• Special inflorescence type: head
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• 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.
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Floral variation
• Flowering dogwood (Cornus florida)
• Inflorescence: white structures are modified leaves (bracts)
that act like petals.
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Pollination
• Why flowers so varied? Many form mutualism with animals to
achieve pollination
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Mutualism Exceptions
• Some flowering plants are wind pollinated (anemophily)
• Some are water pollinated (hydrophily)
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”
Rewards
• Pollen: high in protein
• Also has lipids, minerals, starch
• Can be renewed by:
– sequential anther dehiscence (multiple stamens)
– poricidal anthers (buzz pollination)
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!
Rewards
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• Renewable reward!
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)
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)
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
Pollination
• Benefits of animal pollination for plant
– 2) Style of flower as “selective racetrack”
Pollination
• 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
Pollination
• 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?
Pollination
• Benefits of animal pollination
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Pollination
• 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!
Pollination
• 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
Pollination
• 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)
Pollination
• 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.
Pollination
• Style of flower as “selective racetrack”
• Is there evidence that this works?
• Example, Coyote melon
• Gourd growing in U.S. deserts.
Pollination
• Style of flower as “selective racetrack”
• Study done in 2000 showed that
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• 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).
Outcrossing
• Major benefit of sexual reproduction: generate genetic
variation
• This enhanced by mating with others (outcrossing)
Outcrossing
• How to favor outcrossing:
• 1) Dioecy
Outcrossing
• How to favor outcrossing:
• 2) Floral morphology
• Heterostyly: Distyly and tristyly
Outcrossing
• How to favor outcrossing:
• 3) Floral phenology
• Protandry: anthers dehisce first
• Protogyny: stigma becomes receptive first
Outcrossing
• How to favor outcrossing:
• 4) Self-incompatibility: prevents germination of self pollen or
slows self pollen tube growth
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
Specialization
• Benefits of taxonomic specialization
– Better service: can match phenology of plant/pollinator
– Decrease competition (must match flower/pollinator traits)
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– Better service: can match phenology of plant/pollinator
– Decrease competition (must match flower/pollinator traits)
– Plant: Minimize stigma clogging with heterospecific pollen
Pollination
syndromes
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Pollination syndromes
• Bee pollination: Melittophily
• Bees:
– intelligent, agile
– visual animals: good eyesight (including UV light)
– good smellers (good sense of smell)
– day-active
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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).
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Pollination syndromes
• Fremontodendron decumbens (endangered chaparral shrub)
flowers
• UV reflectance photo (right)
Pollination syndromes
• Beetle pollination: Cantharophily
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Pollination syndromes
• Beetle pollination: Cantharophily
• Beetles are:
– Clumsy
– Have poor vision
– Dumb(er)
– Active during the day (many flower-visiting ones).
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Pollination syndromes
• Beetle pollination
• Beetle pollinated flowers are:
– Relatively large or grouped into large inflorescences
– Light colored
– Smelly (fruity or spicy smell)
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Pollination syndromes
• Bird pollination: Ornithophily
• Birds are:
– agile
– long-beaked
– visual: see red colors well
– poor “smellers”
– Hummingbirds (native to Americas) can hover!
Pollination syndromes
• Bird-pollinated flowers are:
– red or orange
– have nectar hidden by long floral tube
– little or no fragrance
– no landing platform
Pollination syndromes
• Bird pollination: not always by hummingbirds
• Other birds from other areas:
– Sunbirds (Africa/Asia)
– Honeycreepers (Hawai’i).
Pollination syndromes
• Butterfly pollination: Psychophily
• Butterflies have: good vision, good sense of smell, long coiled
tongue. Must land on flower to visit it (can’t hover).
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• Butterflies have: good vision, good sense of smell, long coiled
tongue. Must land on flower to visit it (can’t hover).
Pollination syndromes
• Butterfly-pollinated flowers:
– Color varies (blue, yellow, orange)
– Landing platform present
– Nectar at bottom of floral tube
Pollination syndromes
• Fly pollination: Myophily
• Flies have good sense of smell, especially flesh flies
• Attracted to rotting meat (lay eggs in meat, larvae are
maggots).
Pollination syndromes
• Fly-pollinated flowers: Sapromyophily
– Smell like rotting meat
– Look like rotting meat (dark red, purple)
– Offer no reward: flies fooled by flower.
Fly flower story: Rafflesia
• Ex, Rafflesia of Sumatra
• Root parasite
• Flower is only above-ground part.
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Fly flower story: Rafflesia
• Ex, Rafflesia of Sumatra
• Largest single flower on Earth.
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Pollination syndromes
• Fly pollination
• Largest inflorescence is made by fly-pollinated plant
• Corpse-flower.
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Pollination syndromes
• Bat pollination: Chiropterophily
• Bats are flying mammals
– Nocturnal
– Eyesight good but echolocate
– Good sense of smell
– Agile, can hover when visiting flower.
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– Good sense of smell
– Agile, can hover when visiting flower.
Pollination syndromes
• Bat pollination
• Bat-pollinated flowers
– Open at night
– Lots of pollen and nectar as rewards
– White or light-colored
– Fragrant (sweet)
– May be pendant (hang from branches).
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Pollination syndromes
• Bat pollination
• Bat-pollinated flowers
– May also be made on tree trunks (tropics): Cauliflory
– Ex, cannonball tree of South America
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Pollination syndromes
• Bat pollination: Mainly a tropical phenomenon
• In U.S., saguaro cactus is one of few bat-pollinated species.
Pollination syndromes
• Moth pollination: Phalaenophily
• Moths have:
– Poor vision (nocturnal)
– Excellent sense of smell
– Long coiled tongue.
Pollination syndromes
• Moth pollination
• Moths:
– Some (hawkmoths) can hover when visiting flowers.
Pollination syndromes
• Moth pollination
• Moth-pollinated flowers:
– Open at night
– Sweet fragrance
– White or light-colored
– Nectar in tube.
Pollination syndromes
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– Nectar in tube.
Pollination syndromes
• Interesting moth story: nectar spur
• Nectar spur is long pouch, at bottom of which is nectar
• Moth uses long tongue to reach nectar
Pollination syndromes
• Interesting moth story: nectar spur
• Nectar spur is long pouch, at bottom of which is nectar
• Moth uses long tongue to reach nectar
• Only if tube is longer than tongue will moth have to push into
flower far enough to pick up pollen
• So, long spurred flowers reproduce better.
Pollination syndromes
• Which leads to longer moth tongues to reach all of the nectar
in the longer tubes
• Which leads to longer tubes......
Pollination syndromes
• Which leads to longer moth tongues to reach all of the nectar
in the longer tubes
• Which leads to longer tubes......
• Some moth-pollinated orchids with long nectar spurs (almost
one foot long!)
• Moth has extremely long tongue!
Pollination syndromes
• Moth pollination
• Angraecum orchid from Madagascar.
Pollination syndromes
• Can read more in magazine for Gene Simmons fans.
Sexual Mimics
• Flowers that mimic female bees or wasps
• Look like females
• Smell like females: chemical mimicry. One study showed
flower more attractive than real female!!
Pollination syndromes
• Sexual mimics
• Males attempt to mate (pseudocopulation), pick up pollen, then
fly to another flower and repeat process
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• Males attempt to mate (pseudocopulation), pick up pollen, then
fly to another flower and repeat process
• No reward supplied!.
Pollination syndromes
• Another trick flower
• Grass pink orchid (Calopogon): grows in pitcher plant bogs in
SE US
• Makes fake stamens on petal.
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