2: Insect innovations and the early orders

Question 1

Describe the synapomorphies of the hexapoda

Answer 1

• Pattern of tagmosis: 6 segmented head, 3 segmented throax, 11 segmented abdomen
• reduction in leg segments
• 2 primary pigment cells of the ommatidia
• 3 legs

Question 2

Define synapomorphy

Answer 2

character shared by all the descendent species (strong evidence for relatedness)

Question 3

Describe 1/2 synapomorphies of the Entognatha
(Springtails, bristletails etc.)

Answer 3

• Reduced / absent compound eyes
• Virtually all have eversible vesicles of some kind (important!)
  = Organ that can be everted out of the body

Question 4

What orders make up the entognatha?

Answer 4

Collembola (springtails)
Protura
Dipulra

Question 5

Briefly describe the collembola

Answer 5

Live in leaf litter and topsoil
Important detritivores - soil C retention and N mineralisation
Collophore (eversible vestibular tube x2):
- Electrolyte balance
- Water uptake
- Adhering to surfaces
- Self-righting after vigorous jumping

Question 6

What are 3 innovations that aided the diversification of insects?

Answer 6

1) Evolution of wings
2) Evolution of wing-folding mechanisms
3) Holometabolism

Question 7

Describe the paranotal hypothesis of insect wing evolution

Answer 7

Though that wings arose out of thoracic outgrowths

Question 8

What function could result in the rapid directional selection of insect wings?

Answer 8

Courtship
Thermoregulation
Aerodynamics
Respiration

Question 9

Describe what happens in the insect pterothorax when the dorsoventral muscles CONTRACT

Answer 9

The dorsoventral muscles contract = nodal hinge pulls down:
- As it pulls down the flexible zone (plural process) allows the wing to snap up
- Entire thorax depresses and wing snaps up

Question 10

How is the insect system of flight different to birds, for instance?

Answer 10

The insect pterothorax produces an INDIRECT form of flight power derived directly from materials rather than muscles

• birds directly use muscles

Question 11

Describe what happens in the insect pterothorax when the dorsoventral muscles RELAX

Answer 11

When the dorsoventral muscles relax (and the dorsal longitudinal muscles contract) causes the wing come down as the nodal hinge shifts in the other direction

Question 12

Describe, generally, how insects change direction during flight

Answer 12

Unlike the power of flight, changing direction IS powered by muscles:

Longitudinal muscles can change the forward/reverse angle of the hinge = allows insects to go up/down or side to side

Question 13

Describe the ephemeroptera

Answer 13

(Mayflies)
- Aquatic with elaborate abdominal gills
- Greatly reduced hindwings
- Long cerci
- Large swarms, emergence tightly synchronised with environ queues
- Due to this, they are thought to be v sensitive to climate change

Question 14

Describe the synapomorphies of the Odonata

Answer 14

(Dragonflies and damselflies)
- Large compound eyes
- Internal fertilisation
- Modified jaws of larvae
- Rectal gills → dense tracheal system, water drawn in muscularly
- 3 Caudal gills
- Jet propulsion

Question 15

Describe the compound eyes of the Odonata

Answer 15

Composed of up to 10,000 ommatidia
- Composed of singular units (ommatidium)
- No optical nerve, each ommatidium has its own axon to the brain
- Good res
= Basically 360 vision

Question 16

Describe copulation in the Odonata

Answer 16

(mate guarding):
Male transfers sperm to secondary genitalia
Grips head of female with abdominal claspers, uses aedeagus to transfer sperm
Stays with female to mate guard until oviposition occurs

Question 17

What is tagmosis?

Answer 17

The process of segmental specilisation in the body regions of arthropods
- Fusion/grouping of segments into functional units called tagmata

Question 18

Describe how the degree of tagmosis varies between arthropod groups:
Insects
Arachnids
Crustaceans

Answer 18

Insects: 3 tagmata - head, thorax and abdomen

Arachnids: 2 tagmata - chephalothorax and abdomen

Crustaceans: varies alot, generally organised into cephalothorax and abdomen OR cephalothorax, abdomen AND telson