Transcript Phylum Arthropoda

Arthropoda
5 major lines of arthropod evolution:
1. Trilobitamorpha
2. Cheliceriformes
a. Merostomata
b. Arachnida
3. Crustacea
4. Hexapoda
a. Entognatha
b. Insecta
5. Myriapoda
Sub phylum Hexapoda
• Diverse group (~1000 families)
– Twice as diverse as all other animal taxa
combined
• Co-evolved with angiosperms
– Flower morphology / pollinators
– Herbivory / 2°plant compounds/resistance and
specialization
– Parasitoidism (20% of insects are parasitoids)
Hexapoda
• Mostly terrestrial
• In every habitat except the subtidal marine
habitat – competition from crustacea?
• 3 tagma: head, thorax, abdomen
– 3 pairs of legs, and usually 2 pairs of wings on
thorax
– no abdominal appendages
Major contributors to insect success
Arthropod body plan
• Small size
• Resistance to desiccation
– Trachea
– Waterproof cuticle, egg shell
– Malphigian tubules
• Flight
– Rapid dispersal
– Escape from predators
– Access to distant food, mates
• Holometaboly:
– Larvae and adults occupy separate niches (most speciose
groups are all holometabolous: coleoptera, lepidoptera,
hymenoptera, diptera)
Holometabula
Hemimetabolous development
e.g. Odonata, Orthoptera, Blattodea
Mantodea, Hemipteroids
-Incomplete metamorphosis
-Wing pads present in pre-adult
-Larvae often resemble small adults
Holometabolous development
e.g. coleoptera, lepidoptera, diptera,
hymenoptera
-Complete metamorphosis
-Inactive pupal stage
-Larvae do not
-resemble parents
-eat the same things as parents
-live in the same habitat as parents
Big picture
• Hugely important ecologically as
pollinators (2/3 of all flowering plants),
detritivores, herbivores
• Important economically and socially (to
humans) as disease vectors (fleas, lice,
bedbugs, biting flies), crop pests (and also
as pollinators and biological control
agents)
Hexapoda
2 classes:
1. Entognatha (mouth parts recessed),
2. Insecta (mouthparts are ectognathous =
exposed and projecting from head
capsule)
Hexapod origins
• From aquatic crustacean ancestor
– Probably freshwater
• Winglessness (apterygota) is primitive
condition
“Pterygota”
• Flight evolved 300-400 mya
• Wings = outpocketings of exoskeleton
• Origins of wings? Multiple hypotheses:
– Used for thermoregulatory purposes then later
co-opted for flight?
– Used to stabilize body during jumping?
– Modified from external gills? (genetic
similarities with crustacean gill structures)
Requirements for flight
• Musculature
– Striated
– Attached to strong exoskeleton with flexible joints
• Small body size
• Impervious to water loss
• Efficient internal physiology for gas exchange
(trachea), nutrient storage and distribution
• Well-developed and integrated sensory
organs to regulate rapid movement
• Low rate of wing-flapping
– Odonata, ephemeroptera, orthoptera,
lepidoptera
– Flapping rate limited by firing rate of neurons
• High rate of wing-flapping
– Diptera, hymenoptera, coleoptera
– Use elastico-mechanical properties of
exoskeleton to stimulate stretch receptors to
produce self-sustaining flight