Insects -WF.

Insects -WF.

Cuticle
1. Multiple functions
  1. Mechanical stability
  2. Protection
  3. Allows new muscle attachment sites
  4. Makes complex structures possible
    1. Legs, wings etc
2. Structure: cement layer, wax layer, wax and pore canals, cuticulin, 15-20nm, epitcutice, 0.1-10um, pro-cuticle, exo (tanned) and endocuticle (untanned), chitin, N-acetylglucosamine, protein matrix
Problems with respiration: gettingO2 through impermeable, airtight cuticle, getting O2 to muscles, varying amount, respiration for water dwellers
1. Structure - all same physiological components: spiracles (solution to cuticle, protection and control), trachea (passage and stability), tracheoles (blind ending, 40-70nm to walls, diffusion to tissues), air sacs (store)
  1. decreases diffusion distance and increases surface area, keep tracheoles close to cells (less aqueous travelling), dragonfly flight muscle mitochondria arrangement, indentations in other flight muscle membranes to only bypass limitations to certain extent
    1. Requirements of system: minimise diffusion distance, maximise conc. gradient, cope with high resp. rate of flight muscles, minimise pathlegnth of aqueous phase (30x greater conc. and 10 000 x greater coefficient)
    2. Diffusion becomes limiting and size (distances for diffusion) increase
      1. Does diffusion limit size: yes, insect tracheal systems when kept in low O2, BUT other limitations also: brain and leg muscles, exoskeletal constrictions = bottlencks at neck and leg joints = morphological constraints,
        modify diffusive forms of respiration to provide solutions: mechanisms of control
        Active ventilation
        auto-ventilation of thorax in flight, muscles compress sacs, beat movements open spiracles
        Abdominal pumping (compress sacs)
        Tracheal compression
        Why is control required? increase supply, prevent toxicity
        Alter tracheolar fluid level: in pumping in tracheolar cells, metabolic fluid, increase to prevent toxicity, decrease to increase delivery
        DGE: closed spiracles, high O2, spiracles flutter, no water or CO2 loss, high CO2, spiracles open, preents water loss, O2 toxicity, adaptation to hypercapnic and hypoxic conditions, maximises gradient, burrowing insects
2. Passive diffusion: rate of diffusion limiting, don't use circulation, T=x^2/2D
  1. Requirements to be met by system
3. Aquatic insects:
  1. Breathing tubes (mosquito larvae)
  2. Gills - allow diffusion through thin cuticle to trachae
  3. Air bubble - wing or hairs, short term, replenishes O2
  4. Plastron - hydrophobic hairs, partial pressure deficit
  5. Haemoglobin - respiratory pigment, larvae of certain midges, bloodworms, anaerobic conditions
Insects and plants
1. Pollination by insects = mutualism
  1. Driving force of evolution o flowering plants, adaptations of plants and pollinators
    1. Plants: chemical and opticalsignals, rewads, sticky pollen, mechanical systems
      1. Attract insects
        Co-evolution alongside one another or exploitation of one anothers features e.g flowers drive bee vision or trichromatic vision already present
        Conflicts of interests - maximise pollen transfer/maximise food - led to cheaters: insect nectar robbing (bees and snapdragons), flowers without reward (orchids)
        Conflict of interest - flowers and species specific transfer, insects and balanced diet, flower constancy due to selection for efficient foragers (compromise between the two)
    2. Insects: mouthparts, pollen collection, honey bee, colour vision,
      1. Obtain pollen and nectar
2. Herbivory: feed on all parts of plant, destroy 18% of terrestrial primary productivity
  1. Plant defences
    1. Mechanical: ligin, abrasive substances (silica and cacium oxalate), trichomes, slippery (crystalline wax blooms)
    2. Chemical:secondary compounds
      1. Qualitative: toxins (blockers), cheap, effective, generalist, fast growing plants
      2. Quantitative: inhibit feeding + digestion, large amounts, expensive, effective against all, slow growing plantsbut dosage dependent (quantitative)
    3. Insects overcoming plant defences
      1. Physiological: microorganism symbioses, large guts, hgh pH, Malpighian tubles remove novel toxins, detoxifying enzymes, cuticlar lining in hindgut
      2. Behavioural: leaf rolling, vein snipping to avoid latex, sequester toxins
        EXPLOITATION OF PLANT DEFENCES: Sequestering toxins allows them to usethem to their own advantage
    4. Tri-tophic
      1. Plant defence where the plants attract predators of herbivores, volatiles attract predators and ants, cues
        i._The signals must be clear and specific: they must be released in large quantitiesby the plant and must only be released in response to saliva, laying of eggs or or oviduct secretion from the feeding of herbivorous insects, ii._The signals must be timed appropriately. iii._The signals must attract parasitoids, thus improving the fitness of the plant. This can for example be experimentally measured by monitoring the quantities of seed production in plants with parasitoids near them, and plants without parasitoids present. iv.an insect signal/cue must move inside the plant such that a large area of the plant emits the volatile compound: otherwise only one leaf will be protected and that leaf will probably be badly damaged before the parasitoid has its effect. By sending a signal within the plant, the quantity of volatile which is emitted is much higher and the whole plant, or a large part of it, is protected.
3. Ant-Plant symbioses
  1. Widespread, tropics, extra-floral nectaries attract, ants attack herbivores
    1. Ants are suited: abundant, superorganism colonies, defend spatial territories, predators, recruitment
      1. Myrmecophytes + ants- wax barriers only certain ants can climb, plant provides shelter (hollow tendrils), ants protect from herbivores (attach fly larvae) and encroaching vegetation and fungi
        Plants have reduced chemical defence, redundant, die if ants removed
4. Co-evolution? reciprocal evolutionary change, chemical defence + herbivores, arms race, escape and radiate or diffuse
  1. Difficult to tell if it is actually coevolution because of diffuse co evolution, potential preadaptations and other factors driving evolution
    1. Most likely where you have parallel cladogenesis
Flight: Denovian, insects with flight = diverse, major evolutionary step
1. Origin of flight
  1. Uncertain origin, lack of transitionary fossils, aquatic origin? gill plates, skim water, unlikely, derived groups, EVIDENCE mayfly fossils, terrestrial origin, thermoregulatory role or primitive aerodynamic function, skydive from predators, developed to wings
2. Design of insect wings
  1. Lightening the wings: modified cuticle (get rid of epidermal cells), minimal membrane between veins (epicuticle fused), replace wing edges with cheaper and lighter bristles
  2. Mechanical properties: no muscles, thorax, mechanical properties provide stability, stiffness, muscle movements drive haemolymph into wings on unfolding, vein networks, longitudinal and cross-sectional, stiffness and rigidity, resistance to torsion, wing fold lines, longitudinal and transverse, fold over abdomen, protect
3. Powering flight
  1. Abdominal pumping to increase blood supply, higher haemolymph sugar concentration (10-100 fold > humans), =higher conc. gradient, disaccharide trehalose, lower osmotic conc.
4. Flight muscles, all in thorax, power muscles, dorsolongitudinal and dorsoventral, distort thorax
  1. Two mechanisms based on force transmission, direct and indirect
    1. Upstroke: indirect, dorsoventral
    2. Downstroke - direct, indirect or both,
      1. direct: muscles directly attached to base of wing, pulls down wing when muscle contracts, direct = evolutionarily more primitive, dragonflies, independent control of wings, aerial gate, move wings out of phase
        bees and butterflies couple fore and hind wings, move as one
      2. Indirect, energy into deforming thorax, complicated hinge system, most insects use indirect
        Energy efficient: store elastic energy from one half stroke and use propel next half of stroke
        Gave rise to asynchronous flight mechanism (see limitations of synchronous), asynchronous, higher wing beat frequencies, myofibrils stretch dependent, change in muscle length triggers contraction, no nerve impulse, no refractory periods, quicker
        Differences in sychronous and asynchronous reflected in ultrastructure: not dependent of nerve impulses and thus calcium, less sarcoplasmic reticulum, greater power output + more efficient
        Beetles, bees and butterflies using asynchronous aren't limited by frequency of nerve cell firing so maintain high wing beat frequencies
5. Lift
  1. Mechanism of generating lift: upward stroke and downward stroke together in horizontal stroke plane, streamlines of air, angle of attack, downward acceleration, upward force, lift greatest before stall
    1. Lift mechanisms: bumblebee paradox, wings too small, not enough lift, assumed in still air, vortex generates enough lift
      1. Unsteady mechanisms
        high angles of attack, vortex at leading edge of wing, accelerates air flow at edge, more lift, maximal before stall, keep leading edge attack
        Clap, peel and fling - clap behind back, peel apart front edge, increase air flow around leading edge, additional lift
        Wing rotation: raise angle of attack before and after stroke reversal, rotational lift peaks, lift
        Wake capture - high wingbeat frequencies, wings moving through air with higher velocity than wing, more lift

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	Created by Emily Lythgoe over 8 years ago