Insect evolution and diversity

Biological diversity - insect evolution+diversity

• insects = largest proportion - animal life

• insects - class - phylum arthropoda - characterised, exoskeleton+jointed limbs:
  • insects - 6 legs (hexapods)
  • body divided segmentally - head, thorax, abdomen
• spiders+scorpions+mites/ticks = arachnida
• millipedes+centipedes = myriapoda

• common anatomy despite modifications - adaptation. antenna, ocelli, head, thorax, abdomen
• major difference between insects+chordates (vertebrates) - nerve cord = ventral side+guts = dorsal
• other organs = analogous not homologous

• insect head - formed - plates, exoskeleton - some articulate
• sensory organs = simple+compound eyes, antennae - head

• mouthparts - adaptation - according, diet
• all have palps+mandibles, labrum+labium - shape = changed - food source

• thorax divided - 3 segments - pro, mesa, meta - pair legs. wings - mesothorax+metathorax - not modified limbs

• ocelli (simple eyes)+compound eye
• compound eyes - detecting movement - unable resolve images - acutely - vertebrate eye
• insects percieve colour - UV

• Eclosion hormone (EH)
• Ecoysis Trigger hormone (ETH)
• Ecdysone

• exoskeleton = waterproof protective layer - formed - several layers. thicker endocuticle = mixture, chitin+proteins = cross linked - exocuticle = sclerotised
• surrounded - hard exoskeleton - problem = growth. remove old cuticle before growth = ecdysis

• insects related - other arthropods - segmented body - paired limbs+exoskeleton. most likely related - annelid worms
• arthropods divided - several classes - cambrian explosion

• 1st terrestrial arthropod fossils approx 400 mya - show already advanced insects (wings) - difficult date actual split - fossil record/evidence = poor - emergence insects
• cephalisation (distinct head)
• insects developed due - fusion = front 5 segments - head+reduction - number, segments+paired limbs - 3 segments (thorax). head - 5 ganglia 

• examined genetic material - arthropods - insects likely branched off - crustaceans. living crustaceans = remipeds - closest relatives
• insects+spiders = much more distant common ancestors

• springtails - no longer considered - true insects = sister group 
• jumping bristletails+silverfish - primitive wingless insects
• insects - flying stage (adult)+aquatic nymph stage
• not complete metamorphosis - development - show distinct instars (wingless nymphs - resemble adults)
• advanced groups - undergo complete metamorphosis

• Thysanura = silverfish+firebrats - lack of wings+3 appendages - rear - abdomen. no metamorphism - continuous formation - instars
• Archaeognatha…