Unit III Flashcards
(72 cards)
What factors have been proposed to account for the evolution of sociality in insects?
- Hamilton’s Rule: selection favors altruism (rB>C) where r= genetic relatedness, B= benefit to the recipient and C=cost to the altruist
- Haploidy: in many eusocial insects (like bees and ants) sex determination is haplodiploid. So females are diploid and males are haploid. This means sisters are more closely related to their sisters than their own offspring which results in helping a sista out.
- Limited nesting sites, harsh environments or high predation risk may result in cooperation
Why was the evolution of wings in early insects potentially “exciting?”
- Coevolution with plants during Cretaceous period
- Switching from gliding movement to controlled flapping motion. Lateral appendages like legs (EXCITES) have muscular and trachea
- Allowed colonization of other niches and new habitats (dispersal)
How are respiratory systems theorized to have evolved as hexapods made the
transition from (a) marine habitats to terrestrial habitats and (b) terrestrial to
freshwater habitats
Started out with tracheal system like crustaceans. (hemocyanin) and evolved a tracheal system form invagination of cuticle and then closed tracheal system evolved in immature stages of freshwater bugs
During what periods of earth’s history was the speciation of insects especially
Rapid?
Hexapods on land: 400 MYA during the Devonian period.
* Flowering plants: Speciation linked to flowering plants occurred during the Cretaceous, not the Triassic.
* Gondwanaland distribution: Reflects the breakup of Gondwana and isolation of species.
Why is Wallace’s Line pertinent for the Entomological timeline?
because it divides the Australian faunal region (which is more Gondwanan) from the Asian region. The insect species on each side are remarkably different, reflecting how the landmasses were once separate. Insects that are found in Australia and New Guinea are often very different from those in Southeast Asia, due to the long period of isolation after Gondwana’s breakup.
Which soil horizon has the most hexpods present?
O horizon
What groups are the most abundant in soil and what do they feed on?
Proturans: Collembola (springtails) and Entognatha (Diplura)
Arachnida (Mites)
Thysanoptera (Thrips)
Beetle larvae
diptera larvae
Chironomid larvae (aquatic, but still help break down organics)
Mycetophilidae (fungus gnats)
They are all decomposers helping break down organic material in soils
What are Phylotelmata?
- Pitcher plants (Sarraceniaceae, Nepenthaceae)
- Bromeliads (common in tropical rainforests)
- Tree holes, leaf axils, or even fallen fruit cavities
What are the advantages/disadvantages of a plant using quantitative antiherbivore chemicals like tannins?
✅ Advantages:
* Broad-spectrum defense — affects most herbivores * Difficult to evolve resistance to * Reduces digestibility of leaves → less herbivory
❌ Disadvantages:
* Energetically expensive to produce and maintain in bulk * Less effective against specialized herbivores (e.g., ruminants, some caterpillars)
💡 Think: “Quantity = universal but expensive defense”
What are the advantages/ disadvantages of a plant using qualitative antiherbivore chemicals like cardiac glycosides, alkaloids, and glucosinolates?
✅ Advantages:
* Low metabolic cost (effective at low concentrations) * Highly effective against non-adapted herbivores * Can deter or kill herbivores quickly
❌ Disadvantages:
* Specialist herbivores can adapt to these compounds * May even sequester them for their own defense (e.g., monarchs + milkweed) * Toxicity may harm mutualists (like pollinators or beneficial microbes)
💡 Think: “Quality = potent poison, but specialists may co-opt it”
What nutritional difficulties do insects have when they consume leaves?
🪴 Leaf-eaters (chewers like caterpillars):
* Low nitrogen/protein content * High fiber/lignin/cellulose – hard to digest (some insects have cellualse) * High tannin or silica levels reduce digestibility * Must consume large volumes → more exposure to predators
What nutritional difficulties do insects have when they consume leaves or plant sap?
Sap-feeders (e.g., aphids, leafhoppers):
* Phloem sap: high sugar, low amino acids → protein deficiency * Must process lots of fluid → produce lots of honeydew * Need symbiotic microbes (e.g., Buchnera in aphids) to supplement missing amino acids
Which two families of insects are most frequently leaf miners?
- Lepidoptera
- Diptera
How do leaf galls form and which groups of insects are most galling?
- Initiation: A female insect lays eggs in young plant tissue (usually leaves, stems, or buds).
- Chemical manipulation: The insect injects hormone-like compounds (e.g., auxins, cytokinins) or its saliva alters plant gene expression.
- Plant response: Instead of growing normally, the plant diverts resources to form a specialized structure — the gall — which:
- Protects the insect larva from predators & weather
- Feeds the larva via nutrient-rich tissue
What subphylum includes hexapods? What are three possible sister groups to hexapods?
Evolved from Crustacea
Subphylum: Arthropoda;
Brachipoda, Remipedia, and Cepalocarida are possible sister groups.
What is the earliest hexapod fossil? When was it found?
Rhyniella praecursor=(Collembola)
Devonian, 400 MYA
What is one reason for larger size of carboniferous insects?
Higher O2 in the atmosphere
What was respiration like for earliest insects? How did it evolve over time?
- First insects likely land-dwelling
- Most likely gas exchange across cuticle into hemolymph with green hemocyanin (found in crustacea and a few bugs).
- Tracheal system evolved from invagination of cuticle.
- Gills with a closed tracheal system evolved in immature stages of freshwater bugs.
What are the two theories explaining the evolution of wings in early insects?
- Paranotal Lobe Hypothesis: shelf-like extension off of the thoracic nota (no musculature or trachea)
- Excite Gill Hypothesis: Lateral appendages like legs (excites) have muscles and tracheae.
- Ancestral aquatic insects had leg gills used for respiration and maybe locomotion. Gills modified over time, shifted to thorax and gained articulation and musculature to fly.
What is hemimetabolous?
several distinct nymphal instars, somewhat resemble adults, wing pads external.
What is holometabolous?
actively feeding larvae differ from adults, quiescent pupa, adult. Evolved once.
In which species did pupa-like stage evolve independently?
Thysanoptera
Which of the Hawaiin Islands shows the greatest diversity of families?
the youngest lol
What do soil dwelling insects feed on?
Plant litter and Organic layers
Leaf litter
Decaying Wood
Plant ROots
Fungal Hyphae and fruiting bodies
Dead animals
Dung
