arthropod defenses a glimpse at some chemical defenses types class i: cause some direct harm to...
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Arthropod Defenses
a Glimpse at
Some Chemical Defenses• Types
Class I: cause some direct harm to predator. E.g. toxic venom, caustic liquid, explosive gas, etc. (often accompanied by aposematic coloration) Class II: discourage feeding. E.g. toxic haemolymph, noxious odors
• Sources (Where do they come from?)– Host plants, prey, mother
• Deployment (At what stage are they used?)– Egg, larva or nymph, pupa, adult
• Application (How are they used?)– Bite, sting, squirted, oozed, gassed, passive-internal
Aposematically colored bugs.
Aposemitism: self-advertising, usually through color, that an organism is poisonous or can harm a predator in a way that benefits the survival of the bearer. The effect may be long-lived if the predator learns avoidance, thus protecting other prey. Aposematic colors are usually some combination of red, yellow, & black. Aposemitism may also be involved in mimicry complexes.
A caterpillar with urticating hairs advertised with aposematism.
Many darkling beetles and stinkbugs emit foul-smelling quinone-laden gas.
Cinnabar moth larvae, exotic biocontrol agents of tansy ragwort, sequester toxic chemicals from the plant for their own defense.
Gullen & Cranston 2005
Bombardier beetles (Brachinus spp.)shoot an explosive noxious blastwhen disturbed.
(Hydrogen peroxide + hydroquinones from secretory tissue) + enzymes from wall of reservoir => valve release => explosion in reaction chamber. Near-boiling hot gas is ejected with an audible “pop”. Text box 14.3
Gullen & Cranston 2005
Role of cantharadin in certain pyrochroid beetles. (Neopyrochroa flabellata). Text box 14.4
Defensive chemical in prey protects eggs of next generation.
Environmental acquisition +horizontal transmission +vertical transmission of an multi-function defensive toxin (cantharidin).
Male: defensive protectant aphrodesiac
Female: defensive protectant nuptial gift
Egg: defensive protectant
PATH OF TOXIN: Environment (prey?) => male => courtship/nuptial gift => selection by female => female acquisition through mating => transfer to eggs => egg protection.
“harmful” models
“harmless” mimics
Types of Defense• Against Physical Forces
Threats Dehydration, Drowning, Freezing, Radiation, Wind (blowing
away)
• Against Biological Forces Threats
Microbes Parasites Predators
Strategies Passive Active
Important Points• Virtually all arthropods have adaptations for defense.• Certain adaptations may be both defensive and serve some other function, e. g. flatness of fleas.• Apparent defensive adaptations against humans per se are incidental.
Insect Defence Against Biological Enemies
Disappearing, (Out of Sight - Out of Mind)
hiding, dropping
running, hopping, flying
Costumes:
crypsis & camouflage
mimesis
Passive Resistance, Discouraging the Attacker
Chemical
toxic haemolymph
secretion of noxious compounds
urticating hairs
Morphological
tough, slippery, spiny cuticle
autotomy (part behavioral)
removable scales, hairs
“backwards” appearance
Behavioral
feigning death
Scare Tactics (Morphological/Behavioral)
eyespots
aposemitism
Active Resistance, Resisting attack or Fighting Back
Educatively Injuring the Attacker
slow-acting toxins
bites & stingsKilling the attacker
Collective Strategies, Special Adaptations of Social Species
confusion effects
nest blocking
mass counter-attack
bluff attack
Visual Defenses(Physical Appearance)
• MimicryTrue Mimicry
Batesian
Mullerian
Mimesis & Startle Effect
• Crypsis
• Warning coloration
Some Morphological/Mechanical Defenses
• Tough or Slippery Exoskeleton• Odd shape• Special structures
– Spines (passive or active poking)– Claws (for hanging on to substrate)– Scales (slippery)– Expendable Wing Surface (detachable)– Jumping legs or other springy devices (escape)– Stings (behavioral)
Defense?
Advanced necrosis from brown recluse spider bite. Not the primary function of the defensive adaptation (venom).
Behavioral Strategies
• Passive– Hiding - often with Mimicry, Mimesis, Crypsis– Timing of Development– Migration & Diapause– Autotomy
• Active– Aggressive defense (entails one or more special weapons)– Escape– Startle– Death-feigning
Special Defense Strategies of Gregarious & Social species
(most are mixed strategies)
• Protective Nest
• Large Numbers => startle/confusion effect
• Massive counter-attack, e.g. stinging
• Sophisticated “alarm/attack” signaling
• Soldier caste (specialized for defense)
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