Arthropoda 5 major lines of arthropod evolution: Trilobitamorpha Cheliceriformes a. Merostomata b. Arachnida Crustacea Hexapoda a. Entognatha b. Insecta 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: Entognatha (mouth parts recessed), 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