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Insects and Exoskeletons

            The evolutionary success of insects is largely due to their exoskeleton. This external skeleton consists of three tagmata (body sections): head, thorax and abdomen. The extraordinary diversity of insect form and function has evolved upon this simple body plan (Hickman, 2011). However, the exoskeleton confers advantages and disadvantages upon growth, movement and survival.
             The 'plasticity' of the exoskeleton has enabled insects to colonise almost all habitats on earth (Lattin, 1976). This 'plasticity', or variation in segment shape, size and function while the simple body plan of three tagmata remains constant, has enabled many specialised appendages and sensory organs to develop. The evolution of insect wings 250 million years before birds' wings was a great evolutionary leap in terms of the aerial niche being previously inaccessible for colonisation (Lattin, 1976). Wings, which are extensions of the exoskeleton (Hickman, 2011), allowed insects to fly to new areas to find food and avoid predators. Variation in the size, shape and function of wings, from flies with thin, membranous wings solely for flying, to beetles with rigid forewings to protect the hindwings, emerged by adaptive radiation (Mayhew, 2007). Structural modifications of legs also occurred from those primarily for walking (ants), to legs for collecting pollen (honeybees) (Hickman, 2011). As insects moved into new niches, individuals specialised on particular foods, and adaptive radiation of mouthparts (formed from the hardened cuticle of the exoskeleton) occurred (Mayhew, 2007). By natural selection herbivorous insects evolved chewing mouthparts, predatory insects developed sharp mouthparts for piercing prey, and parasitic insects (mosquitoes) specialised by elongating mouthparts to form a needle to suck blood (Hickman, 2011). Specialised parts of the exoskeleton are also involved in vision (compound eyes), hearing and smell (antennae) (Hickman, 2011).

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