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9/24/08 1 2 3 4 5 6 7 8 9 10 11 12 13 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 1 10 9/24/08 11 12 13 14 15 16 17 18 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). 19 Floral variation • Example of inferior ovary: squash flower (this one is pistillate). 20 Floral variation • Some flowers assembled into groups of flowers: inflorescence • Special inflorescence type: head 2 21 19 9/24/08 20 • 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. 21 Floral variation • Flowering dogwood (Cornus florida) • Inflorescence: white structures are modified leaves (bracts) that act like petals. 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) 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 24 25 26 27 28 3 26 9/24/08 27 28 29 30 31 32 33 • 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 4 9/24/08 33 34 35 36 37 38 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 5 39 9/24/08 38 39 40 41 42 43 44 45 • 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) 46 6 9/24/08 45 46 – Better service: can match phenology of plant/pollinator – Decrease competition (must match flower/pollinator traits) – Plant: Minimize stigma clogging with heterospecific pollen Pollination syndromes 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). 49 Pollination syndromes • Fremontodendron decumbens (endangered chaparral shrub) flowers • UV reflectance photo (right) Pollination syndromes • Beetle pollination: Cantharophily 50 7 51 49 9/24/08 50 Pollination syndromes • Beetle pollination: Cantharophily • Beetles are: – Clumsy – Have poor vision – Dumb(er) – Active during the day (many flower-visiting ones). 51 Pollination syndromes • Beetle pollination • Beetle pollinated flowers are: – Relatively large or grouped into large inflorescences – Light colored – Smelly (fruity or spicy smell) 52 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). 53 54 55 56 8 57 9/24/08 55 56 57 58 59 • 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. 60 Fly flower story: Rafflesia • Ex, Rafflesia of Sumatra • Largest single flower on Earth. 61 Pollination syndromes • Fly pollination • Largest inflorescence is made by fly-pollinated plant • Corpse-flower. 62 Pollination syndromes • Bat pollination: Chiropterophily • Bats are flying mammals – Nocturnal – Eyesight good but echolocate – Good sense of smell – Agile, can hover when visiting flower. 63 9 62 9/24/08 63 – 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). 64 Pollination syndromes • Bat pollination • Bat-pollinated flowers – May also be made on tree trunks (tropics): Cauliflory – Ex, cannonball tree of South America 65 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 66 67 68 69 70 10 9/24/08 69 70 71 72 73 74 75 76 – 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 77 11 9/24/08 76 77 • 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. 12