Plant Reproduction III: Pollination and Mating Systems (Lecture 20)

Pollination and Mating Systems Learning objectives: Be able to: Categorize flowers into the appropriate pollination syndrome Compare cross-pollination and self-pollination, including the advantages and disadvantages of both Describe the ways plants can promote outcro...

Pollination and Mating Systems Learning objectives: Be able to: Categorize flowers into the appropriate pollination syndrome Compare cross-pollination and self-pollination, including the advantages and disadvantages of both Describe the ways plants can promote outcrossing Compare sporophytic and gametic self-incompatibility  Pollination Syndromes The common sets of adaptations of flower structures to aspects related to pollination Can predict what pollinates a particular flower based on floral form Coevolution – has affected both plants and pollinators - The plant that best attracts a pollinator will pass its genes onto the next generation. - The pollinator that best exploits the reward offered by plants will likely have better fitness. ollination Syndromes Flower Pollinator Extremely long spur Extremely with nectary long at the base proboscis Wind Pollination (anemophily) Petals, sepals reduced Lots of pollen produced Pollen is lightweight, non- sticky Stigmas large, often feathery ater Pollination (hydrophily) ect Pollination (entomophily) Bee Pollination Flower construction open – parts visible Often colored but not red Sweet floral odor Nectar Guides or patterns often present Bee Pollination Sunflower Family) – often the heads form an open bowl, pollinated by bees Bee Pollination Bumblebees often forage specifically for pollen, which collects on their hairy bodies, and which they periodically stop to gather into a special pocket on their hind legs called a corbiculum – visible in this image of a California poppy as the conspicuous orange ball. Bee Pollination Nectar Guides Foxglo ve Rhododendron Bee Pollination UV Patterns Co-Dependence Map showing range overlap of Monkshood & Bumblebees Bee Pollination Buzz Pollination Bee Pollination A Special Case:Pseudocopulation Orphrys speculum Fly Pollination Flowers resemble carrion Reddish to purple-brown Strong/Foul odor No Nectar Guides Stapelia schinzii (Carrion Flower) Fly Pollination World’s Largest True Flower – Rafflesia Moth Pollination Open at night Usually White Strong/sweet odor Lots of nectar Moth Pollination Evening Primrose ttps://www.youtube.com/watch?v=8IPQTs0cfqw&t=517s ummingbird Pollination Flowers produce nectar, hidden in long floral tube Often red, orange, or yellow No odor Often lack landing platforms ummingbird Pollination Columbi Trumpet Creeper ne Bat Pollination Open at night White Strongly scented Lots of pollen Bat Pollination Baobab Bat Pollination ther types of Pollination  Summary of Pollination Syndromes Vector Common Colors Odor Nectar Structure Floweri Guides ng Time Wind/ Dull No No Reduced Perianth Any Water Bee Blue, Yellow Sweet Yes Short, often Day complex Fly Brown, Reddish Rotten No Flesh-like Day Moth White, Pale Sweet No Deep Tube Night Bird Red, Orange, None No Deep Tube Day Yellow Bat White, pale Strong No Large, open Night The Flower as a Sexual Structure  Outcrossing Selfing Mixed Mating = both OC and SC Mating System = the proportion of seeds are the result of outcrossing vs. selfing (genetics) Breeding System = more general term for factors that Types of Selfing Geitonogamy = selfing between two flowers on the same plant Autogamous selfing = selfing that happens within a flower Autonomous selfing = selfing that happens without pollinator intervention Facilitated selfing = selfing that requires a pollinator  Cleistogamous flowers vs Chasmogamous flowers Polygala polygama  Mating Systems Plants can “outcross” or ”self” to varying degrees based on species and situation Obligat Facultati Mixed Facultativ Obligate e ve Mating e outcrossi selfing selfing outcrossi ng Cleistogamy ng Dioecy Genetic Self- incompatibil ity Mechanisms to Promote Outcrossing 1.Flower morphology 2.Reproductive timing 3.Genetic mechanisms Mechanisms to Promote Outcrossing 1. Flower morphology Separate your male and female organs in space dioecy monoecy (doesn’t eliminate geitonogamy) herkogamy = spatial separation of the stamens and carpels in a bisexual flower hanisms to Promote Outcrossing: Flower Morphology carpel stamen Carpellate flower Staminate flower nt sexualities beyond monoecious and dioecious scribed and named by Darwin  Androdioecious: Male and bisexual flowers on separate plants Female Gynodioecious : Female and bisexual flowers on separate plants Male Andromonoecious : Male and bisexual flowers on the same plants Bisexual Gynomonoecious : Female and bisexual flowers on the same plants Androgynomonoecious: Male, female AND bisexual flowers on the same plant Andromonoecious Androgynomonoeciou Androdioecious Gynodioecious Why might these exist? Gynomonoecious hanisms to Promote Outcrossing: Herkogamy Extreme type of herkogamy = heterostyly Forsythia “Legitimate Pollination” Pin Thrum Cowslips, Primula veris; thrum-eyed and pin-eyed.  Mechanisms to Promote Outcrossing 2. Reproductive Timing Separate your male and female organs in time - Dichogamy Anthers dehisce before stigma is receptive – protandry flowers are functionally male, then functionally female Stigma receptivity ends before anthers open - protogyny flowers are functionally female, then functionally male Arum maculatum Dichogamy Cabomba Brasenia Female phase flower (1stMale phase flower (2nd day) day)  Dichogamy Strict Protogyny Female Male erlapping male and female function = Delayed Selfing Female Male  Digitalis (Foxglove) Male phase Maturation Female phase Each flower is protandrous Bees move up the inflorescence (females produce more nectar) echanisms to Promote Outcrossing 3. Genetic Mechanisms Self-Incompatibility Pollen and stigma genotypes must be compatible for successful fertilization  Self-Incompatibility ~ 60% of angiosperms have the ability to prevent self- fertilization through genetic mechanisms (SI) Two types: Sporophytic SI (SSI): depends on sporophyte (2n) genotype If the diploid parents share one S-allele – all pollen germination arrested (alleles can be dominant, recessive, or co- dominant – very complex interactions) Gametophytic SI (GSI): depends on gametophyte fig22.20 (n) genotype incompatibility determined by the allele in the pollen. If the pollen tube shares an S allele with the style, then  Sporophytic SI: depends on 2n genotype Both SSI and GSI are controlled by a single, polymorphic locus, S. Each haploid pollen grain has one S allele, the diploid carpel has two S alleles The stigma is the site of SSI If any of the S alleles match, no germination  Gametophytic SI: depends on n genotype The style is the site of GSI Pollen tube and carpel S allele must match to stop PT growth  There are so many mechanisms to promote outcrossing, why do we ever see selfing? eorge Ledyard Stebbins: plant evolutionary biologist Part of the Modern Synthesis Applied genetic principals to the theory of evolution Considered most important book on plant evolution of the When does the shift from outcrossing to selfing occur? Outcrossing  selfing (unidirectional transition) Pioneer species annuals pollination limitation Female pollinator limitation Male Delayed Selfing = reproductive assurance