Plant-Animal Interactions Flashcards
Types of interactions
- Herbivory
- Protection against herbivores
- Pollination
- Seed dispersal
- Plant carnivory
What is the estimated value of pollination?
$168.75 billion in 2009
What is pollination?
Pollen movement from anther to stigma
What is the other name for wind pollination
Anemophily
What is insect pollination called?
Entomophily
Features of wind pollination
Abiotic
Gymnosperms and some flowering plants (grasses, trees) use wind pollination
Flowers are small and grouped together
Not very efficient method (chancy and wasteful)
Biotic pollination
Animal pollination Usually a mutualism Insects - bees, wasps, butterflies Birds - hummingbirds, honey creepers Mammals - monkeys, bats, mice Other - slugs, reptiles, frogs
What is floral advertising?
Advert requires that there is a signal that animals can detect
And there must be a reward for learning to detect the signal
Different animals have different senses so signalling must vary
Different pigments produced by plants for flower colour
Carotenoids
Flavonoids: flavonols and anthocyanins
Bilirubin
Betalains
Carotenoids
Found in daffodils Important in photosynthesis Can help dissipate excess light (photoprotective) Amount of carotenoid determines colour Found in flowers and fruits
Flavonoids
Flavonols and anthocyanins
Usually synthesised and stored in vacuoles
Host of different functions
Importance in defence against pathogens
Part of signalling pathway in rhizobia
Protect against high levels of UV by producing antioxidants (anthocyanin)
Also can form complexes with metal ions and help plants survive in metal-contaminated soil
Colour of anthocyanins
Vivid red and oranges
Colour of flavonols
Mainly reflect UV, so cannot be seen by humans but important for insect/bird pollinators
Can act as a colourless co-factor (contributes to flower colour by stabilising anthocyanins or other pigments in the flower
Bilirubin
Bluish colour of bruises (metal-based pigment)
Betalains
Colour of deep red beetroot
Found in some cacti species
Shape of cells on petals
Difference between conical cells or flat cells on surface of petal changes colour of petal
What colours can a bee see
UV, blue and green photoreceptors (trichromatic)
Flower that uses echolocation
Marcgravia evenia
Disc-shaped leaf
Ring of flowers, shedding pollen
Cup-like nectaries
What else is a tactical cue to bees besides colour?
Flower petal microtexture
Co-evolution in animal-plant interaction
- Plants evolve elaborate methods to attract animal pollinators
- Animals evolved specialised body parts and behaviours that aid interaction with flowers
False floral advertising example
Orchid Chiloglottis trapeziformis deceives male Neozeleboria cryptoides wasps into thinking they are mating with a females
Chiloglottone js the active component that is produced by the orchid and female wasps
Pollinator syndromes
Pollination by beetles: cantharophily Pollination by bats: chiropterogamy Pollination by water: hydrophily Pollination by bees: melittophily Pollination by ants: myrmecophily Pollination by birds: ornithogamy Pollination by butterflies: pyschophily
Pollination by bees
Melittophily
They live on the nectar and feed larvae the pollen
Guided by sight, smell and touch
Flowers predominantly pollinated by bees usually have landing platforms
Radially symmetric / zygomorphic
Flowers are yellow or blue with UV nectar guides
Pollination by birds
Ornithogamy They live on the nectar Large orange or red tubular flowers Dilute nectar secreted during the day Usually odourless
What are special ways in which bees collect rewards from plants?
Buzz-pollination
Oil-harvesting
What other rewards besides nectar do plants offer insects?
Pollen, oil or wax
Nursery / brood-site
Heat - metabolic reward
Cheating by pollinators
Pollinators can cheat the flower and rob nectar without carrying out pollination
Plant mimicry
False advertising: flowers of unrewarding orchid Disa nervosa mimic rewarding flowers of iris Watsonia densiflora
Some flowers mimic insect shape and colouring e.g. Ophrys speculum pollinated by Campsoscolia ciliata
What are perfect flowers?
Have both male and female parts in them
Inbreeding depression example
Unfavourable effects come from inbreeding
E.g. Banksia spinulosa selfing led to a 63% reduction in seed set
What can self-pollination lead to?
Reduction in seed size, fruit set, fruit quality
Methods to prevent inbreeding and ensure outcrossing
- Timing of flowering
- Morphological differences
- Biochemical
- Developmental
Pollen-pistil interaction prior to fertilisation
- Pollen capture
- Pollen adhesion
- Pollen hydration
- Pollen germination
- Pollen tube penetration of the stigma
- Growth of pollen tube towards the ovule
- Entry of pollen tube into the ovule leading to fertilisation
The S locus
SI is controller by a single locus, S, with multiple alleles, S(1), S(2), S(3), etc.
The S locus is highly polymorphic: populations maintain around 40 S alleles by negative frequency-dependent selection
Summary of double fertilisation events
- Pollen tube penetrates synergid and released sperm nuclei; the tube nucleus degenerates
- One sperm fuses with the egg to form a diploid zygote
- Second sperm fuses with the two polar nuclei to form a triploid endosperm, which nourishes the developing embryo sporophyte
The endosperm
Following fertilisation the triploid endosperm nucleus divides repeatedly to form a mass of protoplasm and nuclei without cell division and acquiring nutrients from the sporophyte. As the seed matures the endosperm undergoes cellularisation.
Food resources are thus only laid down in an ovule/seed after fertilisation
What is a fruit?
A structure formed from parts of the flower or influorescence that contains the seeds
Ovary = fruit
Ovule = seed
What percentage of human food comes from seeds
70%
Pre-dispersal hazards
- Incomplete pollination
- Self pollination (eg. by geitonogamy) leading to ovule abortion or incomplete fruit set
- Resource limitation or stress leading to ovule abortion or incomplete fruit set
- Pre-dispersal seed predation
What is a fuses carpel-like structure containing many ovules called?
A pistil
How does pollination affect fruit set?
- Sufficient pollen important for well formed fruits
- Outcrossing appears to be important for fruit quality and longevity (Klatt et al., 2013)
- Low quality fruit may be aborted
Resource limitation
Fruits/seed produced late in the season often have reduced size due to competition for resources. This can be made worse by additional stresses (temperature, water, disease) impacting on resource availability
Pre-dispersal predation
- Florivory
- Insects lay eggs on flower bud
What is a florivore?
Eats mainly the products of flowers
Geitonogamy definition
The fertilisation of a flower by pollen from another flower on the same plant
Methods of seed dispersal
- Wind
- Water
- Explosive
- Animals transportation
Seed dispersal by wind examples
- Dust seeds
- Plumed/woolly propagules
- Plane winged propagules
- Seed-carrying tumbleweeds
Seed dispersal by water
Traits enabling flotation: air pockets, spongy mesophyll, oils and lipids
Common in plant propagules (40% of British fruits and seeds float for more than a week)
Example of plant with explosive seed dispersal
Himalayan balsam
3 methods of seed dispersal by animals
- Immediate ingestion at source, transportation in gut
- Deliberate removal to another site, with the intention of investing some/all of propagule later
- Inadvertent removal on outside of animal body - seed designed to stick to skin/fur of animal
How do ants move propagules to new locations?
Myrmecochory - seed dispersal by ants
Seed coated in elaiosomes - may have scent of decomposing insects which attracts ants
Ants collect the seed and take it back to the ant nest, where they feed on the elaiosome coat and dispose of the seed outside of the nest where it can germinate
Immediate ingestion of seeds
- Colour and scent guide animals to ripe fruit
- Propagule size
- Reward
Chromoplast
A coloured plastid other than a chloroplast, usually with yellow or orange pigment
Pigments in tomatoes
Colour changes from green to red in tomatoes
Due to accumulation of carotenoids in chromoplasts of tomatoes
Chlorophyll autofluoresces red, carotenoids autofluoresce green)
Why does colour change also happen in flowers?
To show which flowers have been pollinated eg lantana
Toxic secondary compounds in fruit: why are they there?
- Provide foraging cues
- Regulate timing of germination
- Force dispersers to visit wider range of food sources
- Alter rate of seed passage through gut
- Toxic to seed predators
- Defend against microbial seed pathogens
What percentage of insect species are herbivorous?
50%
Host plant specialisation: generalist
- Polyphagous: wide range of host plants from different families
- Uncommon
- <10% of herbivorous insects feed on >3 different plant families
- Most common in Orthoptera and Lepidoptera
Host plant specialisation: specialist
- Monophagous/oligophagous: one or few closely related host plant species
- Very common
- > 80% British herbivorous insects
- Dominant in psyllids, aphids, leafminers, leafhoppers
Example of species with divergence in leaf colour to camouflage in different habitats
Corydalis hemidicentra
Example of convergence of two plant families in alpine screes
Fritillaria delavayi (Liliaceae) Saussurea quercifolia (Asteraceae)
What causes many camouflaged leaf colours?
example
Anthocyanins combined with other pigments eg. chlorophyll
E.g. Corydalis hemicentra
Example of achieving camouflage without anthocyanins
Scarious bracts of Monotropsis odorata
Silky-lanate hairs covering Saussurea medusa
Example of imitation of leaf-mining damage
Leaves of Caladium steudneriifolium eaten by leaf-mining moth larvae, which leaves white marks across them
Plain leaves produce patterns (variegation) mimicking the presence of leaf-mining larvae so other insects will lose interest
Categories of plant resistance
Direct: negative effect on herbivores Indirect: positive effect on predators/parasites Constitutive: permanent resistance Induced: response to herbivory Mechanical / chemical
Mechanical resistance: leaf toughness
- Cell walls reinforced with cellulose, lignin, suberin, callose
- Sclerenchyma: fibres and scleroids
- SiO2 crystals: abrasive
Mechanical resistance: leaf surface
- Glabrous (smooth)
- Glaucous (with epicuticular waxes)
- Pubescent (hairy)
- Glandular (with glandular trichomes)
Leaf toughness study
Howlett et al. 2001
As leaf toughness (g) increases, % establishment of Tasmanian Eucalypt leaf beetle decreases
Epicuticular was crystals
Slippery
Mixed effects
Studies show both increased and decreased resistance
Ensikat et al., 2011
Mechanical resistance: trichomes
Impede movement and act as barrier, or increase attachment
Hooked or glandular trichomes can trap and kill insects
Mixed effects - studies show both increased and decreased resistance
What percentage of all known natural compounds have a botanical origin?
> 80%
Chemical resistance: mode of action - quantitative
- Digestibility-reducing
- Dose-dependent effect
- 5-40% of dry plant weight
- E.g. tannins, lignin, cellulose
Chemical resistance: mode of action - qualitative
- Toxic
- Dose-independent
- <2% plant dry weight
- E.g. alkaloids, terpenoids, toxic amino acids
Example of specialist evolving to utilise toxins
Monarchs (Danaus plexippus) sequester cardiac glycosides from milkweeds (Asclepias) as a protection against predatory birds
Stages of defence from herbivore attack
Local wound response (Jasmonic acid mediated)
Volatile release
Predator/parasitic attraction
Within- or between- plant signalling
Between plant signalling
Herbivore-induced plant volatiles (HIPVs) can lead to several effects:
- Direct defence with toxic and repellant effects
- Indirect defence by attracting natural enemies of herbivores
- Signals that provide information on imminent insect attack to undamaged plant tissues
- Signals that provide information on imminent insect attack to neighbouring plants
- Upon perception of certain HIPVs, neighbouring plants prepare for attack, a phenomenon called PRIMING
Advantages of ants over other plant defenders
Abundant
Aggressive
Social
What is the name for using ants as defenders / ‘ant love’ ?
Description
Myrmecophily
Facultative, non-symbiotic mutualism
Extrafloral nectar (EFN) attracts ants
Advantages for the plant of myrmecophily
- Extrafloral nectar or volatile release can be timed according to need
- EFN is cheaper and easier to produce than toxins
- Toxins problematic for floral defence
- Potentially more difficult for herbivores to evolve immunity to ants or parasitoids than to toxins
Arms race example
Passiflora / heliconiine race
Morphological adaptations of Passiflora species against herbivory
Morphological adaptations of Passiflora species against herbivory:
-Egg-mimic structures on stipules of Passiflora davidii
-Extrafloral nectaries of Passiflora coriacea
-Hooked trichomes of Passiflora lobata
-Trichomes on reticulate bracts, leaves and stem of Passiflora foetida
-Variegated leaf of Passiflora coriacea
Adaptations of Heliconiine against Passiflora defences:
-Gregarious behaviour
-Long spikes
-High visual accuracy
-Inspections pre-oviposition
-Gustatory receptors on female legs
-Odourant receptors on antenna
-Wrap trichomes in silk
-Eat tips of trichomes
Services provided by ants and other insects
Protection against herbivores Pollination Seed dispersal Nutrient supply Protection against plant competitors
Name for seed dispersal by ants
Myrmecochory
Diffuse mutualism
Ants eat elaiosomes (lipid-rich)
Ant gardens
Complex mutualism involving one or more ant species, a host tree (phorophyte) and one or more ant-dispersed epiphytes
Ant plants
Myrmecophytes
Symbiosis - ants live permanently on plant
Plant provides nesting space: domatia
Plant provides food: EFN, coccids, food bodies
Ants provide defence and nutrition
Types of domatia
Hollow leaves
Hollow internodes
Chambered tubers
Hollow rhizomes
Food bodies for ants
Lipid- or protein-rich so costly
Limited to nutrient-rich habitats
Production can be stimulated by presence of ants
Types of food bodies
- Belgian body - Acacia
- Beccarian body - Macaranga
- Müllerian body - Cecropia
- Pearl body - Ochroma
How can the plant protect ants?
Mechanical barriers such as slippery wax crystals protect partner ants from competitors
How do ants protect plants?
Prune viruses
Defend against herbivory
What ant protects Macaranga plant?
Crematogaster
Why must carnivorous plants capture insects?
They live in nutrient-poor environments and need N and P
Definitions of carnivorous plant
Must attract prey
Must trap prey
Must digest prey
Must benefit from trapped and digested prey
Pitcher plant genus name and prey attraction
Nepenthes
- Nectar produced above trap
- Colour (UV) signal from the peristome to attract insects
- Odour produces scent that is attractive to insects
Passive traps
- No intrinsic movement
- Employ physical barriers, slippery surfaces and glues
How does Nepenthes trap insects?
Insects slip on peristome (hierarchical ridge structure) -Ridges provides capillarity -Steps provide directionality Peristome traps activated by wetness Drown in the fluid
How does Dewy pine trap insects?
Drosophyllum lusitanicum
Sticky flypaper traps
Insect adhesion
- Adhesive pad: smooth surfaces
- Claws: rough surfaces
Active traps
Employ movement
Physiological activation
Trigger mechanism
Venus fly trap (active trap)
Dionaea muscipula
Prey attraction: red colour, nectar glands
Trigger hairs: 3 per lobe, contain mechanosensory ion channels
Process of trap activation in venus fly trap
Touch stimulus - mechanosensory ion channels open - Ca2+ influx - receptor potential - action potential - aquaporin opening / water transport - change in hydrostatic pressure initiates movements - geometry-driven snap-buckling completes movement
Retention of captured prey
Wax crystals
Pitcher fluid
Carnivory or defence?
Passiflora foetida
Uses sticky hairs/glands as a form of defence
Herbivorous insects taking a bit either get stuck or get their mouthparts stuck together
Carnivorous plant traits originated in plant defence traits
