2: Insect ancestry and phlogeny

Question 1

Define synapomorphy

Answer 1

A derived characteristic shared by a group of organisms, who have a common ancestor

Question 2

Insects don’t have a simple definition, describe how they are generally categorised.

Answer 2

Related to arachnids, crustaceans, chelicerates etc, but they are distinct

Characteristics:
- Usually have 6 legs at some point in life
- Tagmosis: 3 main insect tagmata
- 1 pair of antennae
- Usually have 2 pairs of wings on thorax as adults

Question 3

Why are insects important?

Answer 3

• Model systems
• Insects are vectors for disease (affecting humans, livestock, crops etc.)
• Pollinators
• All groups are declining!

Question 4

Describe some of the characteristics of Palaeodictyoptera

Answer 4

EXTINCT
- Distinct head, antennae, compound eyes
-2 pairs of wings
- Chewing mouthparts
- Elongated abdomen + cerci (tail)

Question 5

Name 2 exant groups that resemble the Paleodictypotera

Answer 5

Mayflies (Ephemeroptera) and Dragonflies (Odonata)

Question 6

What are the 2 theories on where insects arose from?

Answer 6

1: That the arthropods have several origins (and by extensions so do insects)

OR

2: That Arthropods have a single origin, and so form a monophyletic group all from same ancestor (Crustacea)

Question 7

What about insect limbs supports that they were derived from a differnt ancestor to arthropods?

Answer 7

Insects uniramous limbs, compared to arthropods which are biramous

Question 8

Which hypothesis about insect origin is thought to be correct? Give some evidence

Answer 8

2: Single origin from crustacea
Evidence:
- Molecular phylogenic systematics supports that Crustaceans colonised land AS insects
→ which solved the paradox of there being virtually no marine insects and few terrestrial crustaceans

• Neuroanatomy: Brain and visual system wiring of insects very similar to crustaceans and very dissimlar to worms

Question 8

Give some examples of habitats where we are likely to find transition species

Answer 8

Bridging habitats such as…
Estuary
Marsh
Intertidal zone
Mangrove

Question 9

How have insects evolved to limit water loss, due to terrestial life?

Answer 9

The insect integument:
- Secretion of waterproof, waxy epicuticle
- Variable levels of sclerotization
- Extensive network of pores

Question 9

Describe what the insect integument is made from and what this results in

Answer 9

• Chitin based
• Extensive scleotization (crosslinking between chitin and proteins = sclerotin)

= Tough flexible
= Apodemes and ultrastructure as adaptable support

Question 10

How is the insect integument different from crustacea?

Answer 10

• No calcite (biomineralisation)
• More extensive protein x-links
• Waxy epicuticle

Question 11

What is the function of the malpighian tubules?

Answer 11

Excretory system for maintaining electrolyte balance

Question 12

Describe the function of the insect tracheal system

Answer 12

• Network of gas exchange spricales, tubes and tracheoles
• Ventilation can be through tidal flow through all spiracles or regulated

Question 13

Describethe function of the spriacles in the tracheal system

Answer 13

• Regulation through synchronised opening of front spiracles (intake) and back (outflow)
• Spiracles under muscular control, but air flow is typically passive
• Gas exchange discontinouous
  (water loss)