9/24/08 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). 8 Floral variation • Fusing of petals can form floral tube (nectar made at bottom) • Only long-tongued pollinators can reach it. 9 Floral variation • Flowers with both stamens and pistils: perfect flowers 10 Floral variation • Flowers with both stamens and pistils: perfect flowers • Some flowers imperfect. Either pistillate (have pistil) or staminate (have stamens). 11 Floral variation • Note: some species make pistillate flowers and carpellate 12 1 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 1 2 3 4 5 6 7 8 9 10 9/24/08 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 Floral variation • Example of dioecious species: Persimmon (Diospyros) 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). 20 Floral variation • Some flowers assembled into groups of flowers: inflorescence • Special inflorescence type: head 2 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 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) 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 3 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 9/24/08 • 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) 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) 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 30 Pollination • Benefits of animal pollination for plant – 2) Style of flower as “selective racetrack” 31 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 32 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? 33 Pollination • Benefits of animal pollination 4 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 9/24/08 33 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! 34 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 35 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) 36 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. 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 5 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 9/24/08 38 • 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 41 Outcrossing • How to favor outcrossing: • 2) Floral morphology • Heterostyly: Distyly and tristyly 42 Outcrossing • 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) 46 6 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 9/24/08 45 – 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 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.