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9/24/08
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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).
Floral variation • Example of inferior ovary: squash flower (this one is pistillate).
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.
Floral variation • Flowering dogwood (Cornus florida) • Inflorescence: white structures are modified leaves (bracts)
that act like petals.
Pollination • Why flowers so varied? Many form mutualism with animals to
achieve pollination
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
Pollination syndromes • Bee pollination: Melittophily • Bees:
– intelligent, agile – visual animals: good eyesight (including UV light) – good smellers (good sense of smell) – day-active
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).
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).
Pollination syndromes • Beetle pollination • Beetle pollinated flowers are:
– Relatively large or grouped into large inflorescences – Light colored – Smelly (fruity or spicy smell)
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.
Fly flower story: Rafflesia • Ex, Rafflesia of Sumatra • Largest single flower on Earth.
Pollination syndromes • Fly pollination • Largest inflorescence is made by fly-pollinated plant • Corpse-flower.
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).
Pollination syndromes • Bat pollination • Bat-pollinated flowers
– May also be made on tree trunks (tropics): Cauliflory – Ex, cannonball tree of South America
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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