The evolution of flight

Question 1

The jump from not-winged to winged

Answer 1

•happened in one event
•all winged insects are derived from one ancestor
•known by looking at wing structure…
-too complex to have evolved many times
-highly conserved throughout insects, even highly derived spp

Question 2

2 main hypotheses of how it happened

Answer 2

1. Pleural hypothesis - that wings evolved from gills in aquatic insects
2. Paranotal hypothesis - extensions of thorax that later became wings

Question 3

Pleural Hypothesis

Answer 3

• gills of mayfly found on abdomen - similar to wings, can be moved etc. are both articulated and innervated
• gills have to be articulated to waft water over for respiration - especially in warm water (O2 saturation falls with higher temp)
• wafting gills creates the boundary effect = creates flow
• wings not found on abdomen though…

Question 4

Paranotal Hypothesis

Answer 4

•thorax outgrowths gave rise to wings
•evolution around the Carboniferous - foraging in trees then may have fallen out etc.
-extensions aiding in aerodynamics
-bigger the outgrowths = more aerodynamically efficient

Question 5

Possible selection drivers to make outgrowths growing bigger…

Answer 5

• respiration
• aerodynamics
• thermoregulation (as ectotherms, more wing = more surface to protect head and thorax from heat)
• courtship

Question 6

Molecular genetics evidence

Answer 6

•found the homeotic regulation of development that surppressed wing-like structures on the abdomen
•without suppression, wings would develop on the abdomen
= pleural ?!

Question 7

Neural-anatomical evidence

Answer 7

Insects have balls of ganglia in each segment along their dorsoventral nerve cord.
•the nerve routes for flight muscles have ganglia in the abdomen
-not efficient evolution unless evolved via pleural

Question 8

So how did wings evolve via the pleural H?

Answer 8

Looking at stonefly locomotion on water progression:
•basal = using wings to surf across via wind pushing them
•using the wings in a rowing mechanism
•next flapping wings up and down on the water
•more advanced till actual take-off
-each stage = increase SA of wing and flying efficiency

Question 9

Physical correlates with the pleural H

Answer 9

• wind-surfacing stoneflies have quite hollow veins
• flyers have more rigid veins - necessary for flight
• wind-surfacing wings have more hairs on their wings than flyers

Question 10

Evolution of the wing-folding mechanism

Answer 10

•wings are very delicate structures, don’t want to damage them
•if they can be folded away, would protect them
•can occupy new niches, closed spaces (under leaf litter and in bark etc.)
-paleoptera cannot do this, they have to occupy open spaces