Arthopoda VIII - Hexapoda

Question 1

Hexapod Sister Group

Answer 1

Remipedia: Predatory upside-down swimming organisms

Have very few described species

Question 2

Body Plan Insecta

Answer 2

3 Body tagmata: head, thorax, abdomen 
One pair of antennae only 
Uniramous appendages 
3 pair of thoracic appendages (walking legs)
Loss of all/most abdominal appendages

Question 3

Exoskeleton

Answer 3

Epicuticle (waxes) for water retention
Exocuticle (protein crosslinking and chitin)
Endocuticle (chitonous)

Question 4

Exoskeleton moulting

Answer 4

Secretion of new epicuticle
Secretion of moulting fluid (chitinase)
Digestion of old endocuticle by moulting fluid
Secretion of the new endocuticle
Digestion of old endocuticle completed
Secretion of new endocuticle completed
Fracture of old exocuticle along ecdysial line
Expansion of new soft, endocuticle
Hardening of the peripheral layer of new endocuticle to form exocuticle

Question 5

Adaptations to prevent water loss

Answer 5

Waxy epicuticle to prevent water escaping from the endo and exocuticle
Malpighian tubules that excrete uric acid (dry crystals in feces)
Water reabsorption across the wall of rectum (reclaim water carried into Malpighian tubules and retain water in food)
Gas exchange via internal tracheal tubules with closable spiracles

Question 6

Role of Malpighian tubules

Answer 6

Ammonia converted to urea in tissues (fat body)
Urea released into the hemolymph
Urea actively imported into Malpighian tubules
Decreasing pH along the length of Malpighian tubules precipitates urea as uric acid crystals

Question 7

Terrestrial adaptations (2)

Answer 7

Minimize water loss

Avoid/tolerate temperature extremes

Question 8

Avoid/tolerate temperature extremes (3)

Answer 8

Behavioural: basking, stilting, crouching
Morphological: Insulating exoskeletal hairs
Physiological: Shivering, antifreeze proteins `

Question 9

Insect Flight

Answer 9

Mesothoracic & metathoracic wings (2nd and 3rd thoracic give rise to wings)
A delicate layer of cuticle with little living tissue
Key evolutionary innovation

Question 10

Advantages of flight (4)

Answer 10

Access to food resources that were hard to access
Escape predators
Dispersal into new environments
Easier to find mates

Question 11

Evolutionary origin of wings (2)

Answer 11

Tergal (paranotal) lobes: Lateral growths of tergal sclerite
Wings are jointed and there is no joint structure in paranotal lobes so this poses an issue

Appendage Derivatives: Arthropod appendages have an epipod that is jointed to the thorax and this is proposed to develop into the wing.
Work with the nubbin gene showed that the epipod of arthropod has the same protein factor as wings of insects

Question 12

Diversification of wings

Answer 12

Secondary loss of wings (lice and ants)

Specialization of one pair of wings: Hindwings are sensory in flies and forewings are hardened plates in beetles

Specialization of wing exoskeleton (wing scales in butterfly and moth)