Insect evolution and diversity

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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…

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