Is there a direct advantage in having a non-localized respiratory system (tracheae) instead of lungs (in Arachnida)?
One idea: Perhaps evolution of tracheae cannot be explained through a physical advantage but by constraints of body morphology, e.g. tracheae evolved in a tracheatan ancestor with many similar segments (metamerism) whereas evolution of lungs occurred in arachnids with a comparatively derived (spider-like) morphology.
(Perhaps insects would actually be better off with lungs but lung evolution was inhibited by the presence of tracheae, so insects were stuck with the latter.)
One idea: Perhaps evolution of tracheae cannot be explained through a physical advantage but by constraints of body morphology, e.g. tracheae evolved in a tracheatan ancestor with many similar segments (metamerism) whereas evolution of lungs occurred in arachnids with a comparatively derived (spider-like) morphology.
(Perhaps insects would actually be better off with lungs but lung evolution was inhibited by the presence of tracheae, so insects were stuck with the latter.)
Just a palaeontological thought on this: oxygen levels were way higher (around 30%) at the end Silurian/Devonian boundary when invertebratesfirst left the water to invade land, so some reached very larged sizes (eg Moldybulakia, Edgecombe Nature 2003/ also large eurypterids in the sea up to 2.5m long) and again when oxgyen rose by the Early Carboniferous (330mya) with 2 metre long myriapods like Arthropleura and giant eurypterids. Could the origin of trachea thus be more a case of having arisen when times were optimal for air-bretahing with high oxygen levels then remained as an evolutionary hang over as it was entrenched in the insect bauplan by the time they had began diversifying?
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