Download Phylum Arthropoda

INSECTA
Phylum Arthropoda
1. Insecta, “Palaeoptera”, pp. 184-186
Also see indicated ‘Boxes’ on other pages
2. Evolution of wings pp. 208-211
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Phylum Arthropoda
Arthropod Polyphyly?
Sidnie Manton & others have argued that the
Arthropoda are polyphyletic - i.e. the common
ancestor was not an arthropod but rather a
worm
If so, then the key worm lineages are extinct
Monophyly is the default
Phylum Arthropoda
Arthropod Polyphyly?
Monophyly is the default
Modern phylogenetics: homology is assumed
unless contradicted
= parsimony, because homology =1 event
and homoplasy = 2 or more events
So we assume, e.g. the exoskeleton of
Arthropods is homologous in all groups until a
more parsimonious result, due to evidence
from other characters, contradicts this.
Phylogeny of the
Hexapoda
Error Pterygota one
Branch off
Fig. 7.2
Fig. 7.2
Entognathous mouthparts
Phylogeny of basal Hexapoda
Insecta
Fig. 7.3
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Insecta - Ectognathous mouthparts
Insecta
Apomorphies:
1. Ectognathous mouthparts
2. Antennae of 3 true segments
(annulated antennae)
3. Johnston’s organ
and others….
Insecta
Insecta
Antennae of 3 true segments
– Scape, Pedicel, Flagellum (w/ flagellomeres)
– true segment = with muscle attachment
– Antennal segments = antenomeres
– Annulated antenna (muscles only in scape & pedicel)
Insecta
– Segmented antenna (muscles throughout)
Non-insect Hexapoda (which are…?)
Fig. 2.17
Insecta
Insecta
Johnston’s Organ
-in pedicel
-perceives
movements in the
flagellum
-e.g. Calliphora monitor flight speed
(fig. of mosquito most are smaller)
Characteristics - p. 184
Compound eyes & ocelli in adults
Palpi well developed
Legs with 6 segments
Ancestrally 11 segmented abdomen
Gonopore usually on segment 8 in female
and segment 9 in male
Ancestrally with cerci on posterior
Tracheal system with spiracles on thorax & ab.
Development epimorphic
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Mandible: Monocondylar hinge
/
Dicondylar hinge
(with one or two condyles, or points of articulation)
Pivotal
/
Monocondylar mandibles - Archeognatha
movement in one plane only
Insecta
Fig. 7.3
Archeognatha
• “Jumping Bristletails”
Archeognatha
• Abdomen with styli
(vestigial limbs [exites])
• Monocondylar mandibles
• Compound eyes touch
• Possible sister group to
Zygentoma
• Humped thorax
• Detritivores (inc. lichen, algae)
• 2 cerci, 1 median caudal filament
• Molting continues for life
Archeognatha
Archeognatha
• 500 species, 2 families
(20-35 spp in NA)
• 6-25 mm long
• Nocturnal or crepuscular
• Elongate maxillary palpi
© Alex Wild
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Dicondylar mandibles apomorphic of the Dicondylia
Key to major
Hexapod groups
Insecta
Fig. 7.3
Dicondylia - Zygentoma
Zygentoma
• “Silverfish,” “Firebrats” - often with silvery
scales
• Dorsoventrally flattened (not arched)
• Eyes (if present) not contiguous
• Dicondylar mandibles
• Abdominal styli on segs 7-9
(sometimes 2-9)
Zygentoma
Zygentoma
• Cerci subequal in length to median filament
Scales
• 400 species, 5 families
Anti-predator
defense?
• 5-30 mm long;
detritivores, starches
• Nocturnal, don’t jump
• Difficult to preserve
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First insects:
Terrestrial or
Aquatic? p.208
First insects:
Terrestrial or
Aquatic? p.208
Tracheal system had to develop in air
Fig. 7.2
Key to major
Hexapod groups
Fig. 7.2
(from Pritchard et. al. 1993 )
Family richness
In fossil record
Labandeira & Sepkoski 1993
Fossil History
Oldest winged insects ~ 325-300 mya
(Carboniferous)
Ancient
proto-Dragonflies
72 cm wingspan
Fossil History
Wings = “key innovation”
Thin outfoldings of body wall
w/ network of tracheae & blood
vessels
largest insect
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Wings
Compare species richness
Questions
Morphological origin?
“Apterygota” - ancestrally wingless
<10,000 species
Original function?
Process of transition to new (flying) function?
Pterygota - winged insects (99% of species)
Wings
Appeared once = monophyletic
Pterygota (lost repeatedly)
2 theories on origin of wings:
Wings
exite theory
- fusion of exit & endite lobes
- each with tracheation &
articulation
paranotal theory - thoracic tergal lobes
(not from pre-existing limb structures)
exite theory - articulated gill / leg appendages
Leg exites
Fig. 8.4a
Leg exites
Fig. 8.4b
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Wings
Wings
Recent gene expression studies
have shown support for
homology of gills & wings
Protowing non-flight function?
Suggests wings evolved from gills present in
Crustacean ancestors of insects
Exite theory has most support
(Box 6.1)
protection of legs
covers for spiracles
thermoregulation
sexual display
crypsis
defense - escape jump-> glide
Averoff & Cohen (1997) Nature: 385
Wings
Wings
Routes to flight
Routes to flight p. 210-211
1. Floating - dispersal
2. Paragliding - up->down
3. Running-jumping-flying ground->up
4. Skimming - surface sailing
1. Floating - dispersal
2. Paragliding - up->down
3. Running-jumping-flying ground->up
4. Skimming - surface sailing
1 unlikely, size & friction
3 unlikely, physical constraints (velocity)
2 Aerodynamic theory/ test support
4 Stoneflies (Plecoptera) - some skim
Pterygota
• Most species rich lineage
• Winged, some secondarily apterous (wingless)
• Meso & metathorax = pterothorax
• No styli (styles)
Movie - Odonata flight (Shape of Life)
• No adult ecdysis (molting) - except
Ephemeroptera
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“Palaeoptera”
• First thought to be monophyletic but now
considered paraphyletic (DNA & some
morphology)
• Orders Odonata & Ephemeroptera (& extinct
orders, e.g. Palaeodictyoptera) - extant have
aquatic larvae
• Wings cannot be folded flat
against the body articulation via fused plates
Order Ephemeroptera - mayflies
• Nymphs (larvae) aquatic & long lived - the
feeding stage
• Non-functional reduced mouthparts in adult
– Short-lived, “ephemeral,” hours to a few days
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Order Ephemeroptera
• 3,000 species
Order Ephemeroptera
• Penultimate instar = subimago (subadult), fully
winged - Apomorphy
• Hindwings reduced, sometimes absent
• Imagos form mating swarms (larger from standing
• Nymphs usually with 3 caudal filaments & 1
tarsal claw per leg
Order Odonata - Dragon & Damselflies
• 5,500 species, mostly tropical, predacious
• Nymphs with extensible pre-hensile labium
modified for grasping prey
• Male copulatory organs on segments 2&3 but
gonopore on segment 9
copulate in unique
‘wheel position’
• 360° vision - aerial
hunters
Neoptera
• Wings can fold back flat over the abdomen due
to articulation via separate, movable sclerites
water, more species in running water)
• Feed on algae, detritus, some predacious species
Order Odonata - Dragon & Damselflies
• Two suborders hold 99% of species
• Dragonflies: Anisoptera
– Wings to side, larvae with rectal gills
• Damselflies: Zygoptera
– Wings vertical, larvae with 3 caudal lamellae (gills)
Phylogeny of the
Hexapoda
• Explosive radiation - difficult phylogenetically
Fig. 7.2
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Phylogeny of the
Hexapoda
• Monday:
Neoptera - 90% of Hexapoda
Polyneoptera Paraneoptera - Hemipteroids
Endopterygota (Holometabola)
• Insecta, Neoptera in part, Polyneoptera in
part pp. 184-189
Also see indicated ‘Boxes’ on other pages
Fig. 7.2
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