Lecture 9: Herbivory Flashcards
what are the differences between plants and animals as food sources?
> animals are rich in protein > very little difference in the chemical makeup of different animals > little protein in plants > large amount of carbohydrates > N = limiting factors
how do organisms that eat plants digest them?
ANIMALS > fermentation devices > microorganisms digest carbohydrates > specialised compartments in gut INSECTS > specialised feeding parts to get the nutrition they need > huge diversity in insects > intimate association with plants
what are plant’s strategies to defend against herbivores?
1) direct defences
a) toxins, repellents, digestion inhibitors
b) physical defences, waxy cuticles, trichomes
> herbivores also respond to these direct defences
- most aphids place tarsi on leaf surface while walking
- aphid on leaf with trichome walks on tip toes
2) indirect defences
> shelter for predators (domatia)
> food for predators (extra-floral nectaries)
> attraction and arrestment of natural enemies
what are constitutive defences?
> defences produced even in the absence of herbivore attack and with a fixed cost to plants - trichomes
what are inducible defences?
> defences produced in response to herbivore attack, therefore lower fixed costs - toxins in greater amounts under herbivore stress
describe the relationship between acacia tree and ants
> constitutive indirect defences
myrmecophytism
produce the perfect breeding ground for ants
in exchange ants keep away other herbivores of the plant
what are the defences in different plant parts?
> flowers need to be protected
toxins produced once damaged
investing a lot of constitutive defence in petals as most important area
whereas in leaves, not as important
only has inducible direct defences in leaves.
doesn’t need protecting all the time.
is there evidence that plants benefit from inducible defences?
> when plants are damaged by a herbivore, less herbivory occurred over the fact - inducible defence
plants damaged by herbivores had better fitness in the form of larger seeds than plants that were mechanically damaged or an undamaged control
what is the theory of tritrophic interactions/
once a plant has been herbivourised, it will send out chemical signals, either producing a toxin that will negatively effect the herbivore, or a signal that will attract natural enemies of the herbivore.
> jasmonic acid and its methyl ester are signal molecules in response to herbivory
> VOC (volatile organic compounds) are the basis of tritrophic interactions
how do you analyse and collect VOCs? what does this tell us?
> induce response in plant, collect the VOCs
the plant is not synthesising new chemicals, it is simply producing the same chemicals but at different levels in response to herbivory or other factors.
what are predators attracted to in a plant?
> they are not attracted to the prey itself, but they are attracted to the VOCs that the plant gives off in response to the herbivory attack.
know what happens in the JA and diamond back moth experiment on the Chinese and common cabbage
> Chinese cabbage - low constitutive defence; high induced defence?
common cabbage - high constitutive defence; lower induced defence?
natural enemy attracted to VOCs of herbivore damaged common and Chinese cabbage
