Introduction
COEVOLUTION:
PLANTS AND POLLINATORS
• > 90% of existing plant species are flowering plants
• co-evolution between pollinators and early angiosperms
Why so successful?
– mutation
– natural selection
Fossilized flowers
130mya
Cross Pollination
Cross Pollination
Pollination – pollen transfer
Outbreeding – fertilization of egg and sperm from
genetically different organisms of the same species
Bisexual flowers – contain both pollen-producing
stamens and ovule-containing carpels
Advantages:
recessive genes
genetic diversity
evolutionary flexibility
Some plants can self-pollinate
Reducing inbreeding:
-in some angiosperms, genes expressed in the cells at the stigma
surface only allow genetically distinct pollen of the same species to
germinate
- enzymes inhibit the growth of pollen tube
- anthers mature before carpels
Question: Why do so many plants cross-pollinate?
Anemophily
Advantages
• Wind pollination
Works well in:
- open areas
- low diversity stands
- monocultures
- areas of low-moderate rainfall
– gymnosperms
– approx 10% of angiosperms
Maple keys
NA hickory tree
Mountain cedar
142mya
Disadvantages
Aquatic Plants
- requires windy conditions
- requires open spaces
- distances are a factor
- dry environments better than wet environments
- energy costs to producing pollen
- approx 30 genera use water to transfer pollen
- flowers float at the water’s surface where pollen
transfer occurs
e.g., Vallisneria
ragweed
Alnus viridus
Animal Pollination
Zoophily
-A few species are pollinated under water
e.g., Ceratophyllum –stamens float to surface where
pollen is released
- pollen sinks and contacts stigma
- many aquatic plants produce flowers above the water
- may be wind pollinated or animal pollinated
Evolution of Animal Pollination
Steps in the evolution of zoophily:
- most flowering plants pollinated by animals
- mutualism
- adaptive radiation of angiosperms
- likely evolved from wind pollination and
- from exploitative animal-plant interactions
~ 300,000 animal species serve as pollinators
- ovules secrete sticky sap to catch wind-carried pollen
- sap likely attracted animals
- carpel: likely an adaptation to prevent herbivory
- plants produced nectar
Benefits to Pollinators
Benefits to Plants
1. food reward to animal pollinators
- pollen
- nectar
- edible flower petals
- consumption of organisms on flowers
- no longer dependent on wind
- colonization of new environments
- can now occupy environments with high species diversity, low
wind i.e., rainforests
- direct delivery of gametes
- enhances outcrossing
2. non-food reward
- shelter, shade
- compounds for producing phermones
Costs to Plants and Pollinators
Plants Attract Pollinators
Plants
- rewards may be costly
- attract predators
- by flower scent, color, shape, and arrangement
- flowers are adapted to attract animals that are best
adapted to pollinate them
Pollinators
- foraging costs
- handling costs
~ 700 compounds detected in floral odors
Flower odor categories:
- Flowery scents
- Compounds that mimic sex attractants of insects
- Dung or rotten meat smell
Plants Attract Pollinators
Can Plants Trick Their Pollinators?
1/3 of (30,000) orchids obtain pollination by deception
Flower odor categories:
Flowery scents:
- fragrances result primarily from terpenes, for example:
- geraniol (prod by roses)
- limonene (citrus plants)
- vanillin (vanilla orchids)
- eugenol (cloves)
Flower color compounds
- anthocyanins
- anthoxanthins
- betalains
- carotenoids
Sexual deception: mate mimics
Conferred by hydrocarbons, alcohols, terpenoids
Gorteria diffusa, SA
Can pollinators cheat?
- visit different species of flowers
Male bee-flies try to mate with fuzzy spots on petals
Flowers Control Pollinators
Pollinator syndromes
-By flower shapes and positions
- coordinated traits of flowers and pollinators
- Landing platforms
- deduce pollinator type from the appearance of flowers
- used by botanists to develop testable predictions about
plant and animal pollination relationships
-Nectar guides
-Intricate flowers requiring forced entry
Pollinator Syndromes
Pollinator Syndromes
1. Bees
communicate direction and distance of flowers, medium-length
tongues so can pollinate a variety of flowers, good color
vision, but red-blind, good sense of smell (antennae),
“high blossom intelligence” (recognize flowers with large
rewards), show constancy (recognize and repeatedly visit
favorite flowers)
Flowers pollinated by bees:
- often bilaterally symmetrical
- often blue, purple, lavender, white
- landing platform
- nectar and pollen
2. Butterflies
Diurnal, good color vision, land to feed, “high blossom
blossom intelligence”, constancy
Flowers pollinated by butterflies:
- red, pink, orange, blue colors
- bright flowers in clusters
- landing platforms
Pollinator Syndromes
Pollinator Syndromes
3. Moths
nocturnal, good sense of smell, may require a landing
platform, may hover or land
Co-evolution between yucca flowers and yucca moths
Flowers pollinated by moths:
- often white, light-colored flowers
- strongly scented flowers
- some species pollinate brightly-colored flowers
Night-flying moth
with exceptionally long proboscis
Pollinator Syndromes
4. Flies:
Nectar-feeding flies:
- red flowers, little odor, sense sugar through their feet
- some flies pollinate sweet-smelling flowers
Flowers pollinated by carrion flies:
- dull color
- strongly scent; carrion, feces
- nocturnal
Titan - Sumatra
Stapelia
Rafflesia flower, Borneo
Pollinator Syndromes
Pollinator Syndromes
5. Beetles
6. Birds: hummingbirds, honeycreepers, lorikeets,
sunbirds, parrots
- beetle pollination arose prior to the first flowering plants
- important pollinators in dry habitats and tropical forests
- consumers of ovules, pollen and nectar
Flowers pollinated by beetles:
- white, purple, yellow, orange
- large, flat
- easy access
- strong fruity odour
- thermogenic plants
Diurnal, good color vision, poor sense of smell,
foraging costs high
Flowers pollinated by birds:
- open during the day
- bright red, deep pink color
- place to perch
- nectar, pollen
Monkey beetles pollinate Sparaxis elegans, SA
Carrion beetles
African sun bird
Pollinator Syndromes
Pollinators: Keystone Species
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7. Bats
species that exert an exceptionally great impact on other species in the ecosystem, relative to its
abundance
removal of keystone species (pollinators) can have disastrous consequences on ecosystems
Bats: important pollinators in the tropics
Pteropodid bat
Flying Foxes
nocturnal, fly far distances, color blind, good sense of
smell, require large rewards of nectar and pollen,
important pollinators in the tropics
Flowers pollinated by bats:
- open at night
- white-light color
- strong fragrances
- sturdy flowers
- may have landing platform
– Widespread on the South Pacific
Islands
• often the only pollinator and seed
disperser
– nearly driven to extinction by human
hunting, now protected
wild banana
Pollinator Syndromes
Kapok tree: bat pollinated
used for fibre
Fruits
8. Rodents
Flowers pollinated by rodents:
- Colchicum: nectar volume and concentration increased at night (Annals of
Botany, 2008)
- rodents carry pollen on their fur and in feces
- seed production dependent on rodent pollinators
African lily, Massonia, pollinated by
nocturnal rodent, Gerbillurus paeba
(Amer. J. Botany, 2001)
Colchicum plants, SA
- protect seeds from drying out
- are attractive and inviting to animals
- food source
- promote seed distribution
- nourish germinating seeds
- important nutrition for ½ of world’s population
Fruit Dispersers
Coevolution is Important in Global Ecology
Biodiversity: the existence of flowering plants in nature depends
on the presence of appropriate pollinators
-
Brighamia, Hawaii
pollinator extinct