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Arthropods
28 September 2015

10:53




o

“jointed limb”
Highly diverse
Taxonomy
8 classes
 Trilobita (extinct)
 Merostomata (horseshoe crabs)
 Arachnida
 Pycnogonida (sea spiders)
 Myriapoda
 Entognatha
 Insecta
 Crustacea
o Quite unreliable
 Insects and crustaceans most “important”
 Exoskeletons

o

o Consists largely of chitin
 Acetyleglucosamine
 Long chains of alpha-chitin wrapped in proteins
 Chains  bundles  fibres  networks  parallel layers
 Fibre plates twisted through 180o – like plywood
 Very tough
o Defining feature
o Advantages
 Retains water
 Protection
 Support internals and muscles
 Joints
 Diversity of forms
o Disadvantages
 Limits growth – moulting
 Weight
 Reproduction
 Gas exchange limited
 Restricted movement
o Moulting/Ecdysis
 http://www
...
org/content/96/23/13103
...
pnas
...
full
• Critical
• Conserved in insects and crustaceans since cambrian
• new cuticle forms beneath old
○ epidermal cells secrete
○ crumpled and folded
• Moulting fluid also secreted
○ Cocktail of enzymes
○ Weakens and decalcifies old shell
• Old cuticle sloughed off
○ Cracks from internal pressure
○ New skeleton soft – swells and hardens over 48 hours

Behaviour
• Body swells by water uptake
Premoult

Ecdysis

Postmoult

- Cracks in shell
- Along weakened
lines

- Pleural suture widens
- Drinks lots of water
- Membranes bulge: expansion
- Swells body larger
- Body swells
- Sides and then back - Cephelothorax lifted
- Hard muscular
lift
contraction
- Wriggling
- Legs and body
- Loosens eyes, antennae
etc
...
Are registered by the brain to control it
 Moult Inhibiting Hormone (MIH)
□ Released throughout intermoult period

 Suppresses Y-organ
 Ecdysone synthesis inhibited

 Cut off eyestalks and MIH is not produced
□ Y-organ active
□ moult
• Crustacean Hyperglycaemic Hormone (CHH)
○ Role in blood sugar control

○ Rises in the passes premoult phase
○ Massive peak during active phase
○ Induces drinking and uptake of seawater
 Traced by barium sulphate label
○ Thought to be produced solely in eyestalks - traced to gut also
○ Injecting CHH speeds up moulting

 Massive swelling
• Bursican and Crustacean Cardioactive Peptide (CCAP)
○ Discovered in insects

○ Induces tanning

Advances in Invertebrate Zoology Page 4

○ Recalcification
○ Bursican cells are in the ventral nerve cord

○ CCAP causes muscular contraction
○ Bothe released postmoult
 CCAP causes wiggling
 Bursican hardens the cuticle
• CCH, ecdysone, bursican, and CCAP all well timed
○ Discovered and pieced together over a long time

•

Advances in Invertebrate Zoology Page 5

Crustacean Reproduction
05 October 2015

10:18

• Crustaceans generally reproduce sexually
• Lots of research due to applications in aquaculture
• Reproductive organs beneath abdomen
○ Gonaphores
• Male

○

○ 2 obvious pleopods, which insert into the female
○ 2 smaller pleopods run through the hollow large ones - act as pistons to pump sperm through
○ The penises run up into the large pleopods from behind the hindmost leg

○

• Female

Advances in Invertebrate Zoology Page 6

• Female

○

○ Lots of pleopods, with chaetae on them
 Ventilate eggs, held under abdomen when berried (pregnant)
○ The gonophores are calcified, so mating occurs post-moult
 Pheromones, related to Uridine Diphosphate (UDP) are excreted from the antennal glands
 Attracts males
 Supresses males' hunger for moulting crab
 Male defends them

○

 Bursa's purpose is largely unknown - potentially sperm storage
 Sperm from successful males is stored in the spermatheca, with a cap forming across the vagina to
prevent further mating
...

/\
|

GIH from eyestalk blocks

Fiddler Crabs
• Intertidal zone
• Mate attraction through waving
○ Open-flat mating - vertical wave
○ Burrow mating - lateral wave
• Herding behaviour
○ Manoeuvre female crabs into their burrows

Advances in Invertebrate Zoology Page 8

Advances in Invertebrate Zoology Page 9

Insect Development and Ecdysis
09 October 2015

14:03

Holometabolous Development
• Endopterygota development (wings later)
• Complete metamorphosis
• Egg --> 1st instar - - - > 5th instar --> pupa --> adult

•

Hemimetabolous Development
• Exopterygote
• Wing develops through nymph stages
○ Small adults

•

Ecdysis Hormonal Control
• Prothoracicotropic Hormone (PTTH)
○ Secreted from brain
○ Operates on Prothoracic Glands - activates
○ Equivalent of Moult Inhibitory Hormone in crustaceans - inhibits
• Ecdysone
○ Produced in Prothoracic Gland
○ Initiates cuticle development
• Eclosion Hormone
○ Secreted from brain
○ Triggers emergence from pupa/old cuticle
○ Causes ETH release
• Eclosion Triggering Hormone (ETH)
○ Released from Inka cells
○ Acts on central nervous system to cause wriggling and pulsation
• Juvenile Hormone (JH)
○ Wrigglesworth 1936 - 5th and 1st instars fused, sharing blood
...

○ Kept animals in juvenile state
○ Released from corpus allatum
 Atrophies to allow adulthood
○ Acts on Imaginal Discs
 Precursor tissues to adult form
 Receptors for JH

Advances in Invertebrate Zoology Page 10

○

• Bursicon and Crustacean Cardioactive Peptide (CCAP)
○ Same as crustaceans
○ Triggered by ETH
○ Contraction/wriggling
○ Cuticle hardening

•

Ecdysone 20OH

PTTH

EH and ETH

Bursicon
CCAP

[Hormone]

Time

Advances in Invertebrate Zoology Page 11

Molluscs
12 October 2015

10:13

Triploblastic Organisms
• 3 germ cell layers
○ Ectoderm
○ Mesoderm
○ Endoderm
• Coelomate
○ True coelomic cavity
○ Allowed organs to form
• Includes
○ Annelida
○ Arthropoda
○ Mollusca
○ Nematoda
• Protostomes
○ Coelom formed through schizocoely



○ Spiral cleavage



○ Development determinate/mosaic
 Developmental fate of each cell already determined
Kingdom Animalia - Subphylum Lophotrochozoa
• Phyla:
○ Annelida
○ Mollusca
○ Brachiopoda
○ Phoronida
○ Bryozoa
○ Entoprocta
○ Many more
...
Coiling
• Twisting of visceral mass and shell
• Thought to have evolved before torsion
• Coupled with elongation of visceral mass
Torsion
• Occurs during embryogenesis
• Asymmetrical development of pedal retractor muscles
• Brings mantle cavity to anterior end
• Problems
○ Restricts growth
○ Generates dorsal visceral mass
○ Excretion above head
• Solutions
○ Directed water current
○ Loss of right gill
• Evolutionary force not fully understood
○ Contraction into shell head first
○ Ctenidia ventilation
○ Anterior facing sensory organs
○ Shifting centre of gravity
○ Arrangement of shell for fast creeping
Conispiral Shell Coiling
• Following the evolution of torsion, the shell changed from a plantispral symmetrical shell to a
conispiral asymmetrical shell
Taxonomy
• 3 recognised classes
○ Prosobranchia - marine snail
○ Pulmonata - terrestrial snails
○ Opisthobranchia - marine snails with reduced/absent shells
• Relationship controversial/unclear
• Prosobranch and Pulmonata clades paraphyletic
• Monophyly for the Euthyneura (pulmonata and opisthobranchia) and caenogastropoda

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Advances in Invertebrate Zoology Page 15

Opisthobranchia
19 October 2015

10:45

Opisthobranch Diversity
• 9 recognised taxa
○ Nudibranchia - true sea slugs, shell-less
○ Notaspidea - side gill slugs, flattened reduced shell
○ Sacoglossa - sapsuckers, kleptoplasty (symbiotic algae)
○ Anaspidea - sea hares, shell reduced internal or external
○ Cephalaspidea - bubble snails, thin shells
○ Acochlidiacea - lack shell and gills, only ca
...

○ Thecosomata - sea butterflies, pelagic swimming slugs
○ Gymnosomata - sea angels, shell lost
○ Rhodopemorpha - ???
Opisthobranch Phylogeny
• Much debate regarding taxa relationships
• Nudibranchia are closely related to pleurobranchoidea
○ Both = Nudipleura
• Acochlidiacea basal grouping
• Actenoidea less primitive than formerly thought

Hermaphroditism
• Many invertebrates are hermaphrodites
○ Potentially costs more
• Majority don't self-fertilise
• Can be:
○ Sequential
○ Simultaneous
• Sequential hermaphrodites typically change sex upon certain size
○ Protandry - male to female
○ Protogyny - female to male
• Opisthobranch reproductive biology
○ Diversification of reproductive strategies within opisthobranchs
○ Majority protandric simultaneous hermaphrodites
 Born male, become simultaneous hermaphrodites
• Evolution of Hermaphroditism
○ Ghiselin (1969)
○ Low density
 Sedentary or sessile organism
 Increases likelihood of a fecund encounter with another individual of the same
species
○ Size advantage
 One sexual function has an advantage related to size
 Eggs need size
 Male can start mating sooner
○ Gene dispersal
 Increases effective population
 Reduced inbreeding
○ Investment gain curves
 Trade-off between gonochorism and hermaphroditism can be described by IGCs
 Dioecious individual
□ Linear response

Advances in Invertebrate Zoology Page 16



□ Saturation response



 Hermaphroditism more likely to develop
 Simultaneous investment into male and female function

□

• Opisthobranch Reproductive Morphology
○ Complex reproductive systems
○ Juxtapositions of male and female functions
 Penis and prostate
 Vagina and egg laying organs
○ Typically 3 opening to reproductive organs
 Oviduct
Advances in Invertebrate Zoology Page 17

 Oviduct
 Penis
 Vagina
○ Sperm and eff develop in ovotestes
 Passes through hermaphrodite duct and stored in the ampulla
○ Male structural features
 Autosperm: sperm produced by individual
 Allosperm: foreign sperm
 Ampulla: stores autosperm prior to ejaculation
 Prostate: activation of sperm? Avoids self-fertilisation in ovotestes
 Penis: barbed to ensure successful copulation
○ Female structural features
 Seminal receptacle: stores and nourishes sperm pre-fertilisation
 Nidamental glands: includes albumen, membrane, and mucous glands
...

 Bursa copulatrix: digests unwanted sperm, often first organ to receive sperm

○

○ Monaulic - 1 duct
 Presumed to be pleisomorphic/ancestral
 Common to bullacea, philinacea, thecosomata, gymnosomata, acochlidacea, etc
...
5 micrometres thick
○ 9 layers recognised
○ 5 common

Advances in Invertebrate Zoology Page 23



• 3 bands of crossed fibres
○ Spiral network
○ Fibres inelastic
• Cuticle impermeable strong
○ Important in hibernation
○ Hydrostatic skeleton
• Appearance varies
Hydrostatic Skeleton
• Containment of aqueous body fluids
○ Impermeable body
○ Usually muscle or collagen bound structure
• Muscle contraction increases pressure
○ Pressure transmission in all directions
○ Cuticle resist pressure change
○ Shape changes
• Peristaltic crawling
○ Common mode of movement
○ Widespread in soft bodied invertebrates
• Antagonistic longitudinal and circular muscles (nematodes don't have circular muscles)
○ Radial or transverse muscles

○

• Disadvantages
○ All directions
○ Local precise movement difficult
○ Energetically expensive
 Deforms whole body
○ Limit to deformation
• No circular muscles means no peristaltic movement
○ Antagonism to longitudinal muscles comes from internal pressure and non-elastic cuticle
• Nematode Cuticle
○ Innermost layers - 3 layers
Fibres spiral alternately
Advances in Invertebrate Zoology Page 24

○ Fibres spiral alternately
 Crossing points are pivots
 Angle changes as worm moves
 Longitudinal muscle contraction increases the angle
 Elongation decreases angle
 Pressure changes by altering volume

Nematode Movement
• In large nematodes
• Contraction at one point - elongation
• Maximum extension of ~10%
• Locomotion
○ Dorso-ventral waves - dorsal and ventral alternately contracting/relaxing
○ Contraction compresses the cuticle
○ Pass posterior down body
• Turgid tube
○ Muscles act upon turgidity
• Restoration to max volume length
○ Muscular relaxation
• Circular muscles not needed
• Limitations
○ Can only perform wave movement
○ Lack manoeuvrability of platyhelminthes - comparable to tongue
Nematode Morphology
• Cross-section similar
○ 5% cross sectional area muscle
○ 10% csa cuticle
• Tangential strength proportional to csa
○ Thicker walls
○ Greater internal pressures
• Muscle force exerted proportional to csa
Bigger animals --> bigger muscles --> higher pressure --> thicker cuticle

Feeding and Digestion
• Variety of food nutrient sources
○ Bacterial suspensions or debris
○ Predators
○ Phytophagous (blood-suckers)
• Traditional complete digestive system
• Mouth
○ Maximum 6 lips
○ Buccal cavity and rectum have cuticle coating continuous with exterior
○ Buccal capsule - taxonomic
• Presence of teeth
○ Rasp flesh
○ Taxonomic
• Muscular oesophagus and pharynx
○ Must resist internal pressure when "swallowing"
• Phytophagous buccal feature
○ Spear-like
○ Hollow stylet
○ Pharangeal pump
• Oesophagus muscles - glands
Lumen
Advances in Invertebrate Zoology Page 25

○ Lumen
• Digestive secretions
○ Amylase
○ Proteases
○ Pectinases
○ Chitinase
○ Cellulase
• Digestion
○ Mouth opens/closes
 Buccal oesophageal muscles
 Hydrocoel pressure assists closing
○ Intestine very simple
 Tube-like
 Single layer
○ Intestinal wall
 Tall simple column cells
 Brush borders of microvilli
○ Digestive enzymes in lumen
 Digestion minor importance
 Rapid rate of food movement
○ Main features
 N2 excretion and absorption
○ Wasteful feeders
○ Haemolymph for transport
• Excretory/Secretory Systems
○ Excretory system
 Unproven function
 Visual estimation
Ectodermal epidermis below cuticle
○
○ No flame duct/nephridia
 Excretory tubules (lateral canals)
 Single ventral gland (Rennette cell)
 Duct extends anterior
□ Open to ventral pore
□ Oesophageal region
 Pore taxonomic
○ Little evidence that the excrete
Reproduction
• Dioecious in most
• Sexual dimorphism
• Hermaphroditic/parthenogenetic
• Development always direct
• Body cavity filled with paired reproductive organs
○ Serially arranged
○ Often coiled

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Advances in Invertebrate Zoology Page 27

Platyhelminthes
02 November 2015

10:12

Size
• Affects locomotion/osmoregulation
• Weight Is proportional to volume is proportional to length3
○ Animal the same shape but 2x as big has 8x the weight
• Surface area or CSA is proportional to length2
○ 2x size, 4x the SA or CSA
• Limitations of size
○ Transportation/heat exchange
○ Circumvent?
 Change shape
 Circular cross-section to flattened ellipse
□ Keep SA:Vol constant
Body Form and Structure
• Bilateral symmetry
• Definite anterior end
○ Sensory and motor nerve elements
○ Highly differentiated (eyes)
○ Prey detection
• 1mm-5m
• Body more than 2 cell layers thick
• Acoelomate animals - triploblastic
○ Well-developed mesoderm
○ Parenchyma
○ Reproductive organs
○ Musculature
• Parenchymal skeleton
○ Loose mass of fibres
○ Cells of varying types
○ Functional/storage
○ Myocytons (non-contractile)
• Intestinal organs embedded
○ Dissection impossible
• No circulatory system
• Nervous system simple
○ Brain - cerebral ganglion
○ Longitudinal cords
○ Simple sensory organs
• Trematodes (flukes)
○ Range of sizes
○ Stoma - mouths (taxonomic)
 Mono-: oral sucker only
 Amphi-: oral sucker, posterior acetabulum
 Di-: oral sucker, acetabulum on ventral surface
 Echino-: collar with spine
 Holo-: ventral surface modified
 Gastero-: mouth on ventral surface

Advances in Invertebrate Zoology Page 28



○ Genital sucker in some species
• Cestodes (e
...
tapeworms)
○ Scolex - hold fast organ
 Simple or absent
 Hooks, suckers, spines, tentacles
 3 types
□ Acetabula - suckers
□ Bothria - false suckers
□ Bothridia - muscular clamps
○ Neck
 Relatively undefined
 Contains neoblasts - similar to stem cells
○ Strobila
 Unique
 Series of genitalia organs
 'segmented' - constrictions
 Proglottid surround
 Strobilation



• Musculature
○ Muscle fibres course through parenchyma
○ Contractile portions rarely striated (myoblasts)
 Longitudinal layers near body surface
 Circular
 Dorso-ventral fibres
○ Digeneans
 Superficial
 Circular and longitudinal
 Diagonal layers
 Sheath of muscle
 Multiple planes of movement
○ Degree varies - robust/strong --> weak
○ Cestodes - deep muscle
 Absent in trematodes
 Continuous
○ Muscles often most prominent at anterior end
 Radial muscle fibres
• Surface Structures
Advances in Invertebrate Zoology Page 29

• Surface Structures
○ Importance of structure overlaying muscle
○ Ciliated epithelium
 Single layer
 Large volumes of ventral cilia
 Sensory cilia
 Glands in mesenchyme
○ Parasitic species
 Resistant 'cuticle-like' surface
 Non-ciliated
○ Genostoma kozloffi
 Crustacean parasite
 Tegument
 Ciliated ventral surface
• Tegument
○ Belong to neodermata (have cuticle)
 Adults have tegument
 Neodermis
○ Trematodes, monogenera, cestodes
 Considered 'non-living' secreted cuticle
 Living complex tissue
 Sunken epidermis - distal cytoplasm
 Cytons - cells connected to distal cytoplasm (nuclei continuous with each other)
○ Variations in tegument
 Spines - oral and ventral suckers
 Ridges/pits - surface area, cannels, and microvilli
 Sensory papillae
○ Lots of mitochondria in neodermata - energetically expensive as constantly restored
○ Vesicular secretions
 May be several
 Variable change
 F
...
at proglottid - no true segmentation)
Gripping Substratum
• Ciliated epithelium
○ 1o locomotion
○ Ciliary gliding
• Muscular contraction along ventral surface
• Mucus - turbellarians
• Cestodes - scolex and microtriches; hold not move
• Monogeneans - haptors (hooks); suckers, hooks, clamps (external parasites)
• Opisthaptor - posterior hooking and clamping organ
• Digeneans - acetabula and oral suckers
• Permanent anchors?
○ Will normally migrate around body
○ Let go and reclamp in next resting place
Digestion
• Exclusively feeders on animal tissues
• Blind ending
○ A few species have only a mouth
○ Cells of parenchyma
• Mouth generally anterior
• Muscular pharynx
○ Mid-ventral
• Gut variation (always blind-ended)
○ Highly branched tube - polyclades
• Rarely have an anus
○ Ingested waste elimination through vomiting
• Apparent inability to synthesise fatty acids and steroids
○ Symbiosis necessary
○ Commensal or parasitic
• Trematodes - blood-feeders
Plug of tissue
Advances in Invertebrate Zoology Page 31

○ Plug of tissue
○ Oral sucker and muscular pharynx
○ Intestine/bladder/rectum and bile ducts
 Mucus and tissues of the host
○ Pharynx not always present
 Muscular oesophagus
○ Digestion extracellular in digestive ceca
 Sime intra- and extra-cellular
○ Secretion of enzymes
 Pre-digestion by Haplomotra sp
...
2003
• Dragonfly will maintain exact retinal position with opponent
○ Appears motionless
• Very accurate computations and motion control
Insect Exoskeleton
• Epicuticle and procuticle
• Secreted by epidermis
○ Also foregut, hindgut, and trachiae
• Procuticle
○ Polysaccharide chitin and proteins
○ Chitin fibre sheets (lamellae) laid down with 10o offset
○ Chitin-protein matrix naturally flexible
 Schleriotisation/tanning in exocuticle - protein crosslinks harden cuticle
○ Trichogen and tormogen cells produce sensory hairs and their sockets
• Epicuticle
○ Lipoprotein, lipid, wax
○ No chitin
○ Gland cells and ducts through cuticle
• Articulated joints
○ Extensor vs flexor muscles
○ Protractor vs retractor muscles

○

○ Body segments - head, thorax, abdomen
○ Leg segments



Skeletal Muscle
• Slow - position/stance maintenance
○ Myofibrils 59%
○ Mitochondria 25%
○ Sarcoplasmic reticulum 13%
 Ca2+, troponin/tropomyosin
Advances in Invertebrate Zoology Page 35

Exocuticle
Endocuticle

 Ca2+, troponin/tropomyosin
• Fast - quick and sudden actions
○ Myofibrils 60%
○ Mitochondria 4%
 Fast contraction, don't need constant aerobic respiration
○ Sarcoplasmic reticulum 21%
Motor Neurons
• Multiterminal, polyneural innervation
○ Multiple contact points between neuron and muscle fibre
○ Multiple neurons acting on the same muscle

○
• L-glutamate neurotransmitter
• Inhibitory (stop muscle from contracting) and neuromodality (change the way the muscle reacts to the
neuron)
• Locust limb
○ Fast extensor tibiae MN (FETi)
 68% of fibres activated
○ Slow extensor tibiae MN (SETi)
 8% exclusively
○ In vertebrate motor units give fine control
○ In invertebrates separate motor neurons have different effects
 FETi - greater neurotransmitter volume, great post synaptic potential
 Frequency of motor neuron potential gives control - each action potential causes small
movement - cumulative effect of multiple potentials
□ <5Hz no response, 15-20Hz contracted to tonus (rigid but not acting on skeleton), >70Hz
rapid contraction, >>70Hz tetanic - locked fully contracted
Self-organised movement
• Group coordination
• Phase change - change in behaviour
...
g
...
2006)
○ alternative source of protein and salt
○ Pursue other individuals
• Sensory ablations (Bazazi et al
...
2001)
○ Travel in the same direction to maintain distance between 'lanes' of pursuing crickets
• Running away from those chasing
○ Simple local processes contribute to coordinated group movement
Developmental Changes
• Holometabolous (complete metamorphosis) and Hemimetabolous (partial metamorphosis)
• Muscles for moulting
• Massive changes
○ Caterpillar - hydrostatic movement
○ Butterfly - rigid exoskeleton and wings
○ Levine and Trueman (1985)
○ Caterpillar - lots of internal muscles
 Butterfly - many internal muscles and associated motor neurons degenerate
○ Adult - lots of external (relatively) muscles important
 Completely rewired
 Muscles degenerate and are replaced, same MN
 Dendrites remodel
□ Larva - side-side bending
□ Adult - coordination for dorso-ventral flexion
• Teneral period
○ Period after moult - neural circuits not fully matured
• Autotomy and degeneration
○ Can lose limbs - muscles and MN degenerate

Advances in Invertebrate Zoology Page 36

Ballistic Escapes
13 November 2015

•
•
•
•

13:48

Adaptations for jumping
Different for locusts and froghoppers
Applications in other rapid movements
Fast energy release

Locusts
• Grasshoppers that swarm
• Cross-bridges provide the force in muscle contraction

•

• Locust hindlegs
○ Extensor tibiae
 Large muscle
 Most of femur
 Causes leg to extend - jump
○ Flexor tibiae
 Small
 Pulls legs into closed position
○ Not many mitochondria or sarcoplasmic reticulum
 One-off contraction, not sustained
○ Pennate muscle structure in extensor

Advances in Invertebrate Zoology Page 37



 Parallel layers take up too much space
 Instead diagonal sarcomeres pull on tendon
 Shorter distance but more sarcomeres, more cross-bridges pulling
 2
...
g
...
g
...
g
...
g
...
g
...
Twisting forward
...
Twisting back
...
g
...
g
...
3mm wingspan 400Hz wingbeat
 Similar in thrips, whitefly, Drosophila
 Periodically in locusts and butterflies
○ Wings clap at top of upstroke
○ Leading edges separate, air sucked in
○ Vortex - accelerated airflow gives more lift
○ Vortex shedding - cast off downward, reactive force upwards

○

Advances in Invertebrate Zoology Page 43

Flight Control
20 November 2015

14:22

Three Components
• Central Pattern Generator (CPG) for flight
• Feedback from poprioceptors
○ Wing hinge stretch receptor
• Descending influences
○ Tritocerebral Commisure Giant (TCG)
CPG
• Flight rhythm
○ Wilson 1980
○ Asic program from circuits in CNS
○ 'Fictive flight' Experiments - blow air over head/excite isolated ganglia
 Robertson and Pearson 1980s
 Elevator and depressor motor neurons alternate



 Evidence for CPG
○ Elements of the CPG
 MNs don't make rhythm
 Interneurons are key
 Riteria for CPG involvement
□ Rhythmically active at wing beat frequency
□ Phase resetting - altering IN alters rhythm
 Oscillating circuits of interneurons
□ Reciprocal connections
□ IN301 excites IN501 (6ms delay)
□ IN501 inhibits IN301 (3ms delay)
□ IN301 switched off
□ IN501 switched off
□ Oscillating network
□ Just small part of complex circuit - >100INs
Feedback from Proprioceptors
• Wing hinge stretch receptor
○ Detects wing elevation
○ Excites depressor MN
○ Inhibits elevator MN
• Learning: flexibility in motor pattern
○ Modified motor output for course control Mohl 1993
○ Right-left time difference affects yaw angle

Advances in Invertebrate Zoology Page 44

Descending Influences
• Tritocerebral Commisure Giant (TCG) - 2 neurons, giant, dwarf
• Respnds to airflow over head
• Flight 'starter'
• CPG component (detects head nodding)
• Left-right direction control
○ 1 on each side

Advances in Invertebrate Zoology Page 45

Amphipods
27 November 2015

13:56

• Crustaceans
○ But no carapace
• Class Melacostraca
• Superorder peracarida
○ Young develop directly, no larval stage
• Order amphipoda
○ Young brooded by mother
○ Marsupium/pouch
• Distributed worldwide
• Mostly marine
• Some aquatic and terrestrial
Ecology
• Diverse feeding habits
○ Herbivores
○ Detritivores
○ Carnivores
○ Omnivores
• Critical role in food webs
○ Consume detritus
○ Fed upon by fish
 Conduct nutrients to higher trophic levels
Antarctic Giants
• Antarctic amphipods
○ Up to 10cm long
• Polar seas - high concentration of O2
• Amphipods able to maintain high concentration of oxygen in haemolymph
○ Can circulate around larger body
Supergiants
• 28-34cm long
• Kermadic Trench, north of New Zealand
○ 6
...
9km deep
Silk Spinners
• Crassicorophium bonelli
○ Spin silk
○ Strong as spider silk
○ Adhesive as barnacle adhesive
 Used to make tube out of sediment
 Possible medical application
Terrestrial Species
• Family talitridae
○ Marine, semi-terrestrial, and terrestrial species
• Sand-hoppers
○ Semi-terrestrial
○ Feed on rotting vegetation along tide line
• Land-hoppers
○ Full terrestrial damp habitats
Abundant in soil habitats of NZ
Advances in Invertebrate Zoology Page 46

○ Abundant in soil habitats of NZ
Subterranean Species
• Stygobites
○ Restricted to subterranean habitats
○ Many amphipod families
• Troglomorphy
○ Loss or severe reduction of
 Eyes
 Pigment
 Body appendages
Gammarus duebeni
• Generalist feeders
○ Detritivore and opportunistic predator
• Found in brackish and freshwater habitats
○ Europe and North America
• Wide salinity tolerance
○ Rockpools above high tide mark
○ Freshwater lakes and rivers
 Ireland, west wales, western Scotland, Cornwall, Brittany, Isle of Man
• G
...
duebeni
○ Very tolerant of stress
 Change in salinity
 Aerial exposure
 Hypoxia
Hyperoxia
Advances in Invertebrate Zoology Page 47

 Hyperoxia
 Heavy metal exposure
 Radiation
○ Outcompeted by invasive species
 Freshwater especially
 G
...
tigrinus
• Intraguild predation
○ Predation at same trophic level
○ Gammarus males - eat moulted females
○ G
...
duebeni
□ More successful intraguild predators
□ More successful male defence
 Females reproduce more rapidly
○ G
...
duebeni
 Females reproduce much more rapidly
○ In freshwater
 G
...
duebeni
 G
...
tigrensis from invading
Pleistophora mulleri
○
 Microsporidian parasite
□ Invades muscle tissue
 Replaces with spores
□ White zones in muscle
 Described from Irish freshwater G
...
duedeni
 Molecularphylogeny of rDNA and Rpbl genes
□ May be synonymous with P
...
2003
□ P
...
duebeni
 Doesn't infect G
...
mulleri is present
 G
...
pulex males
 G
...
tigrinus females less vulnerable to G
...
tigrinus less likely to be displaced

Advances in Invertebrate Zoology Page 48

Lake Baikal
30 November 2015

10:04

Ancient lakes
• Most lakes less than 10,000 years old
○ Fill with sediments
• Ancient lakes
○ Considerable older
○ Often contain species flocks
○ 24
Species Flocks
• Groups of endemic species
• Formed by adaptive radiation from single ancestral species
• Common in ancient lakes
○ e
...
African cichlids

Lake Baikal
• Southern Siberia
• 20-25 million years old
• 1637 metres deep
○ Fully oxygenated (currents)
• 20% of Earth's unfrozen freshwater
• >2500 animal species
○ 20 new species each year
• Species flocks
○ Sympatric speciation - ecological divergence
○ Snails
○ Sponges
○ Flatworms
○ Amphipods
○ Sculpins (benthic fish, grip substrate with pectoral fins)
• Amphipod Diversity
○ 261 endemic amphipod species
○ 20% non-marine amphipod diversity
○ Unspecialised forms
 Predominantly benthic
 Inhabit relatively shallow water
 Broad dietary range
 Coexisting species
□ Divergent colour patterns
□ Often segregated by breeding season

□

○ Abyssal species
 Live at extreme depth, up to 1
...
zienkowiczii
□ Sediment overlaying substrate - P
...
gerstaeckeri
□ Burrows beneath surface - P
...
granulosis
○ Occasionally produces severe muscle infection
 Large quantity of tough spores
 Suggest horizontal transmission
• Can 2 feminisers co-exist?
○ Mathematical models suggest that they cannot
 Parasite with highest transmission and feminisation ability displaces the other
completely
○ Horizontal transmission
 Can allow coexistence
 If better feminiser has weaker horizontal transmission

Co-evolution of Amphipods and Feminisers
• If feminisers are transmitted solely transovarially they should be inherited with mitochondrial
genes
• N
...
duobenum
○ Not coinherited with CO1
○ Present in many amphipod species, no evidence for co-evolution
Interactions of Feminisers and Environment
• Low temperatures
○ Inhibit parasite replication in embryo
○ Reduces effectiveness of feminisation
○ Can result in incomplete feminisation - intersexuality
Paramyxea in Orchestia
• Paramyxea parasite
○ Vertically transmitted, mother to offspring
• Causes feminisation
○ In Orchestia gammarellus - semi-terrestrial talitrid amphipod
• Microsporidium Dictyocoela gammarellum
○ Present in some host species
Does not feminise
Advances in Invertebrate Zoology Page 53

○ Does not feminise
Paramyxea in Echinogammarus marinus
• Microsporidium Dictyocoela muelleri
○ Associated with feminisation and intersexuality
• Paramyxea parasite
○ Also associated with feminisation and intersexuality
○ Frequently co-infects D
...
villosus invasion route

Invasion of D
...
villosus
Advances in Invertebrate Zoology Page 57

Genetic Diversity and Enemy Release - D
...
villosus populations
○ No evidence for bottlenecks or enemy release
○ Slow expansion across continent
• English Channel and North Sea
○ Salinity too high
○ Founder effect
Microsporidian Prevalence in Mainland Europe
• Wattier et al
...
villosus populations
• No macroparasites
• 4 species of microsporidian parasites detected by PCR
Microsporidian Prevalence in Great Britain
• No microsporidia detected by PCR
• Lower prevalence in more recently colonised areas
Genetic Diversity in Great Britain
• Slightly lower than Europe
○ Heterozygosity
○ Allelic diversity
• Population structure
○ Different allele frequencies in UK populations
○ Suggest multiple invasions
Predicting Future Invasions
• D
...
g
...
gahi genetic divergence in South America
 Barriers don't affect all species similarly
□ Adult movement and/or larval dispersal maintains connectivity
• Genetic homogeneity across SW Indian Ocean - Octopus cyanea
○ No adult dispersal
○ Mauritius population isolated by gyre system - larvae cannot disperse
○ Larval dispersal very effective
• Genetic homogeneity across South Australia - Octopus maorum
○ Isolation of West and East Tasmania by conflicting currents
• Mayan Octopus - Octopus maya
○ Populations 10-100s km apart around Yucatan peninsula
○ Benthic larval stage
○ Genetically different Juarez et al

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