Behaviour etc nervous system sensory apparatus integration behaviour - processes and function

Nervous system insect nerve cells are complex insect nerve cells have highest metabolic rate of any known tissue insect nerve cells respond faster than ours (small size of ‘brain’) insect nerve cells can’t send long range pulses quickly insect nerve cells don’t have redundancy

organisation 2 ventral nerve chords + segmental ganglia CNS primitively ‘ladder’ CNS has tendency to become fused ‘brain’ = supra- + suboesophageal ganglia

sense organs mainly setae … many kinds of sensory setae mechanosensory, chemosensory etc campaniform - cuticular stress placoid - chemoreception chordotonal organs - limb position equilibrium sensors (e.g. Johnson’s organ

vision ocelli stemmata compound eyes

ocelli - late instar hemimetabolous insects, adult insects … fast response, some may detect images. Used in horizon detection, flight control stemmata - larvae of holometabolous insects. Largely light/dark detectors, limited image formation compound eyes - larvae of hemimetabolous insects, adult insects. Used to detect images

ommatidia organisation corneal lens crystaline cone - feeds light into rhabdomeres rhodopsins oriented in villi of rhabdomeres 3 colour (sometimes 4 colour) vision UV/blue/green, sometimes red detector cells twist, short (UV) cell detects polarization

apposition compound eyes commonest form in insects operating in daylight each ommatidium provides information from a narrow solid angle about its axis axes not oriented radially, some areas densely sampled by ommatidia arranged almost parallel (fovea) complex neural circuitry combines information from adjacent ommatidia

superposition compound eyes mainly nocturnal insects (& (modified) in butterflies) lens systems of many ommatidia act as little telescopes and generate an erect image on the ‘retina’ (made up of the packed detector elements of many ommatidia) eyes have a ‘clear space’ and produce ‘eye- shine’ resolution not quite as good as apposition eye, light collection ~10-100x better

muscid eyes only found in muscoid flies (houseflies, blowflies, tachinids etc) apposition eyes BUT detector elements don’t twist AND detector elements from adjacent ommatidia that are ‘looking’ in the same direction are hooked up through a complex nerve mesh good light detection capability, good resolution associated with need to collect photons to compensate for effects of rapid turning flight

vision extensive neural processing in optic lobe,feature detection circuits similar to ours motion detection image detection speed of processing (flies have flicker- fusion thresholds > 5 x ours)

insect vision is a field of very active research – and ANU is a world leader we now know insects are MUCH more capable than was thought the case even 10 years ago emulation of insect vision is proving a fertile field in robotic vision other insect senses are likely to prove equally ‘impressive’

behaviour navigation behaviour/ecology –development –maintenance –mating systems

navigation use of vision –landmarks … wasp, bee first flights –use of sun compass –use of polarization pattern if sun not visible –time clock to compensate for sun’s apparent movement other senses - chemical, remembering steps

use of landmarks originally investigated in sphecid wasps Philanthus work - Tinbergen use of landmarks –availability –kinds preferred –hierarchy of landmarks used at different scales –hierarchy of ‘backups’ remembered

sun compass use position of sun in sky to navigate time clock to compensate for sun’s apparent movement (even overnight!) enables flight over long ranges or uniform habitat (ranges of kms) use of polarization pattern in small patches of clear sky if sun not visible

other senses chemical gradients magnetic sense remembering steps REAL navigation almost always involves a hierarchy of different senses, with backups

behaviour and ecology behaviour is a key process underlying ecology example we will take: ‘dragonfly life history’ (will bounce around a range of species)

larval stages Diphlebia is the concrete example females lay eggs in rotten wood floating in pools micro-habitat of earliest larval stages unknown later stages occur under rocks in riffles emerge at night to hunt prey on rocks

adult maintenance thermoregulation –conformers –heliothermy –myothermy feeding –prey detection –interception

mating systems e.g. dragonflies (very well studied) ‘rendezvous’, operational sex ratio male behaviour sperm competition female responses to limit interference mating in dragonflies requires female action … males can hold on to encourage - but may lose opportunities

sperm competition Insects preadapted for strong sperm competition - sperm stored, only a few used per egg, eggs fertilized at laying displacement or extraction of previous sperm mate guarding to prevent take over by another male (with consequent loss of stored sperm)

exercise examination of dragonfly mating systems

References Physiology: Imms ‘Outlines of entomology’ as revised … CSIRO ‘Insects of Australia’ Behaviour: navigation, mating systems/sperm competition Alcock ‘Animal behavior: an evolutionary approach’ dragonflies: Corbet ‘Dragonflies: behavior and ecology of Odonata’