LECTURE 14 - Ecdysozoa: Hexapoda

Question 1

What are Apterygotes?

Answer 1

-The class Apterygota consists of wingless insects that are probably most similar in form to the ancestors of all insects
- Apterygota include firebrats, silverfish, and collembolans

Question 2

What are Pterygotes?

Answer 2

• The winged insects are members of the class Pterygota and their life cycle is more complex
• Hatchlings undergo substantial changes at each moult in the process of growing larger
• The immature stages of insects between moults are called INSTARS
• METAMORPHOSIS is the substantial change that occurs between one developmental stage and another
• Insects that exhibit gradual changes between their instars are said to undergo INCOMPLETE METAMORPHOSIS (grasshoppers, dragonflies)
• Insects that exhibit dramatic changes between theirs instars are said to undergo COMPLETE METAMORPHOSIS (butterflies, moths, flies)

Question 3

Why are insects so small?

Answer 3

• Because they depend on diffusion through tracheae for respiration
• The tracheae form a network of thin-walled chitinous tubes opening at spiracles at the surface of the thorax and abdomen

Question 4

Why are insects terrestrial?

Answer 4

• Again: respiration depends on diffusion through tracheae, which is slower in water than in air because water is more viscous than air
• Freshwater insect larvae have external gills

Question 5

What are some basal Hexapods?

Answer 5

• Collembola
• Protura
• Thysanoptera
• Insecta
• Head capsule with paired antennae
• Thorax with three limb-bearing segments
• Abdomen of five segments bearing various appendages
• Periproct

Question 6

How did wings evolve?

Answer 6

• Aerodynamics
  
  • Gliding
    
    • Distance = lift / drag
  • Parachuting
    
    • Time = √(Drag / Mass)
• Insulation
  
  • Temperature excess = Areal / Loss

-Effects of wings can be measured using models in a wind tunnel

• Likely that short wings evolved initially for insulation, thus providing the basis for evolving longer wings for gliding, and subsequently flapping flight

Question 7

Why are there so many species of insects?

Answer 7

• Perhaps because dispersal is easier in water than in air
• The effect of gravity is countered by buoyancy in the sea

Question 8

Why are there so many species of beetles?

Answer 8

• Beetle diversity has greatly expanded since the origin of the group in the Permian
• Most of this increase is attributable to the radiation of Phytophaga = herbivorous beetles
• The phylogeny of chrysomelid beetles shows that the earliest-branching clades fed on conifers, with later lineages evolving to utilize cycads and angiosperms
• This implies that the diversification of herbivorous beetles was associated with the Cretaceous radiation of flowering plants

Question 9

Explain the co-evolution of insects and plants

Answer 9

• Chemical defence of system of Brassicaceae
  
  • Compartmentalized myrosinase and Glucosinolates (non-toxic)
    
    • TISSUE DAMAGE —> isothiocyanates (toxic)
• Counter-defence system of Lepidoptera (diamond-back moth, Plutella)
  
  • Compartmentalized myrosinase and Glucosinolates (non-toxic)
    
    • TISSUE DAMAGE —> isothiocyanates (toxic)

BUT ALSO
- Glucosinolates (non-toxic)
- Glucosinolate sulfatase –> Non-toxic metabolites

• Counter-defence system of Lepidoptera (Cabbage White, Pieris)
  
  • Compartmentalized myrosinase
    
    • TISSUE DAMAGE –> Nitrile breakdown products (non-toxic)
  • Glucosinolates (non-toxic)
    
    • TISSUE DAMAGE –> Nitrile breakdown products (non-toxic)
    • Nitrile-specifier protein (NSP)

Question 10

In Angiosperms, what appears to be primitive?

Answer 10

insect pollination