Arthropoda: Hexapoda (Set 3)

Diversity of Hexapoda?

Insecta - 99%

Entognatha (inside jaw) - 1%

What are the three tagmata of hexapoda?

1. Head

2. Thorax

3. Abdomen

All segments have 1 leg pair

Abdomen has 11 segments

What are the main sublasses of Class Insecta?

• Coleoptera (beetles) - 38%

• Lepidoptera (butterflies) - 16%

• Diptera (true flies) - 15%

• Hymenoptera (wasps, ants) - 12%

• Hemiptera (grasshoppers, etc.) - 10%

What are the key innovations for Insecta for success?

• Compound eyes

• Wings

• Metamorphosis

What is direct vs indirect wing movement?

Direct: Muscles attached to the wings themselves

Indirect: Contraction of muscles move tergites, which wings are attached to

What are the two hypotheses of Insect wing evolution?

• Novel Structure Hypothesis: Expansion of lateral folds

• Appendage Hypothesis: Evolved from preexisting appendages, like gills or legs

Insect reproduction

• Gonochoristic; internal fertilization

• Oviparous

• Haploploidy in hymenoptera

  • Males come from unfertilized eggs (parthenogenesis), females from fertilized eggs

• Metamorphosis → Ametabolous, Hemimetabolous, or Holometabolous

What are the different kinds of development in Insecta

Direct Development = Ametabolous (no metamorphosis/change in morphology from immature to adult)

Two types of Metamorphosis (indirect development → abrupt change in morphology)

• Hemimetabolous (Nymph/Naiad → Adult) - Larva looks quite similar to adult but functions differently, doesn’t have wings; dragondlies and grasshoppers

• Holometabolous (Larva → Pupa → Adult) - larva and adult do not resemble each other; flies and butterflies

What are the hypotheses for Insect Diversification?

• Acquisitions of key innovations (compound eyes, wings, and metamorphosis)

• Radiation into newly formed terrestrial niches (myriapods are first arthropod to transition to land, insects came soon after) → coevolve with plants to fill niches that were made

How do hexapods walk/run?

• Walking - metachronal waves from posterior to anterior (like myriapods)

• Running - tripod gate (move front and back on one side with the middle of the other)

What is the function of the waxy cuticle?

Exokeleton: Waxy cuticle

Epicuticle: Waxy, reduces water loss

• Solution to drying out (one of the problems with transitioning to land)

• Remember staying low to the ground with jointed legs as a way they dealt with gravity!

How can insects prevent water loss with internal respiratory structures?

Have tracheae with closable spiracles; trachea tubules allow oxygen to be delivered directly into the insects muscle and helps to prevent water loss through closable action

Insects excretion?

Malpighian tubules; convert ammonia to uric acid to decrease toxicity → Solves problem of excretion with little water when transitioning to land

Diversification of mouthparts

• Have four possible mouth parts: Labrum, Labium, Maxilla, Mandible

• Same structures but can have different functions to encompass any feeding strategy → highly diverse

How can insects communicate (chemical, auditory, visual)

• Chemical: Pheromones

• Auditory: Creating - stridulation (rubbing body parts together), tymbal, drumming, vibrating

• Visual: movement, light display, color patterns

What are ecological roles of insects

• Nutrient cycling: Soil turning and producing

• Pollination and seed dispersal

• Decomposition

• Pest control

• Food source for other animals