Insect Part 2

What are the two types of cells in organisms based on their role in reproduction?

Germ cells (reproductive) and somatic cells (non-reproductive)

What is meiosis and why is it important for fertilization (zygogenesis)?

Meiosis is the process that creates haploid gametes, enabling zygote formation upon fertilization

What does the phrase "Our body as a vehicle for germ cells" mean?

The soma supports and protects the immortal germline that is passed on to the next generation

What are pole cells and their significance in embryogenesis?

Pole cells are the precursors to germ cells, migrating to the gonadal region during development

What are insect ovarioles and their function?

Ovarioles are structures where oocytes develop; they function like assembly lines for egg production

Where are germline stem cells located in insects?

In the germarium at the tip of the ovariole

What is vitellogenesis?

The process where vitellogenin is taken up by oocytes and stored as yolk for embryonic development

What is the difference between oviparity and viviparity?

Oviparity involves egg-laying; viviparity involves live birth

What regulates vitellogenesis in female mosquitoes?

Hormonal signals and nutrients after a blood meal (e.g. via the fat body and hemolymph)

How does the XY sex determination system work in insects like fruit flies?

Males are XY, females are XX; Y chromosome does not determine maleness—gene dosage does

What is the ZW sex determination system?

Females are ZW, males are ZZ; found in species like silkworms

How does the XO system determine sex?

Males have one X chromosome (XO), females have two (XX); common in grasshoppers

What is haploid parthenogenesis or haplodiploidy?

Males develop from unfertilized (haploid) eggs, females from fertilized (diploid) eggs; seen in bees

What is diploid parthenogenesis?

Asexual reproduction where offspring are diploid without fertilization, e.g., in pea aphids

What gene influences male behavior in fruit flies?

The fruitless (fru) gene

How does fruitless gene expression influence behavior?

High FruM expression leads to male-specific courtship behavior

What are key functions of the Sex Peptide (SP) in insects?

Promotes egg laying, reduces female receptivity, aids fertilization, alters female behavior

Where is the Sex Peptide Receptor (SPR) expressed?

In Dsx/Fru-expressing neurons that regulate female post-mating behavior

What is the effect of sexual rejection on male insects?

It alters behavior and may reduce reproductive effort or increase risk-taking

What are the two main types of cell-cell communication?

Electrical (via neurons) and chemical (via neurotransmitters)

What are the types of neurons based on structure?

Monopolar, bipolar, and multipolar

What is the resting membrane potential?

The negative voltage across the cell membrane in a resting neuron

What happens in Step 1 of nervous transmission?

Receptor potentials are generated, such as by olfactory receptor neurons

What triggers the action potential in Step 2 of nervous transmission?

Opening of voltage-gated sodium channels

What occurs in Step 3 of nervous transmission?

Neurotransmitter release via voltage-gated calcium channels at synapses

What are examples of insect neurotransmitters?

Acetylcholine, dopamine, serotonin, GABA, glutamate

What are the categories of synaptic transmission?

Excitatory, inhibitory, and modulatory

What is a ganglion?

A cluster of nerve cell bodies in the insect nervous system

What are the roles of glial cells in insects?

Support neurons, insulate axons, regulate ion balance

What structures make up the insect central nervous system (CNS)?

Brain and ventral nerve cord

How does the CNS vary among insect species?

Varies in ganglia fusion and degree of cephalization

What are the major insect senses?

Vision, hearing, touch, smell, taste, proprioception, thermoreception, nociception, hygroreception, gravity

What is the insect integument made of?

Procuticle layers: exocuticle and endocuticle with embedded sensilla

What are cuticular sensilla?

Sensory structures on the exoskeleton (e.g., hair-like bristles)

What are trichoid sensilla?

Hair-like structures sensitive to touch and wind (e.g., on fruit fly bristles)

What is a campaniform sensillum?

A dome-shaped mechanoreceptor sensitive to cuticle deformation

What are stretch receptors used for?

Sensing muscle stretch and body position (proprioception)

What is a chordotonal organ?

A subcuticular mechanoreceptor composed of scolopidia used in hearing and proprioception

How do trichoid sensilla and chordotonal organs differ?

Trichoid are external and hair-like; chordotonal are internal and detect vibrations

What is a tympanal organ?

A specialized chordotonal organ used in hearing (e.g., katydid ears)

What is an example of convergent evolution in insect auditory systems?

Independent evolution of tympanal organs in different insect groups

What is Johnston’s organ and where is it located?

A mechanoreceptor in the antenna that detects motion of the arista

What does Johnston’s organ detect?

Air movement, sound, and gravity

How does Johnston’s organ help sense gravity?

By detecting shifts in antennal position relative to gravity

What is the central dogma of molecular biology?

DNA → RNA → Protein; genes encode proteins

Why is protein shape important?

Shape determines function, like binding or catalysis

What is an enzyme?

A protein that catalyzes biochemical reactions

What is a receptor protein?

A protein that binds signaling molecules (e.g., hormones or neurotransmitters)

What is a transcription factor?

A protein that binds DNA to regulate gene expression

What are pumps and ion channels?

Proteins that regulate ion flow across membranes, essential for nerve function

How did animal eyes evolve across species?

Eyes are quite different among species and evolved independently

What controls eye development in both insects and humans?

A conserved master regulatory gene shared across species

What are opsins and how do they function in vision?

Opsins (GPCRs) combine with retinoids to form rhodopsin, which undergoes photoisomerization to detect light

Why did high-resolution vision evolve?

To adapt to ecological needs; led to different eye types like compound and camera-type

What is a compound eye?

An insect eye composed of many ommatidia, each acting as an optical unit

What structures make up an ommatidium?

Corneal lens, crystalline cone, pigment cells, rhabdom with photoreceptors

How do human and insect eyes differ in resolution, field of view, and color?

Humans: megapixel, <180°, blue-red

Insects: kilopixel, up to 360°, UV-yellow

What color ranges do insects see that humans can't?

Insects can see UV light, unlike humans

How do bees use vision to find nectar?

They detect UV patterns on flowers that guide them to nectar

What are dorsal ocelli?

Simple eyes in insects that detect light intensity; consist of a lens and rhabdom

What are stemmata and where are they found?

Simple eyes in holometabolous larvae; used for basic light detection

How did insect and human chemoreceptor genes evolve?

They evolved independently and are quite different

What do olfactory chemoreceptors detect?

Airborne substances at low concentrations; found on antennae and maxillary palps

What do gustatory chemoreceptors detect and where are they found?

Substances in solution; on mouthparts, legs, pharynx, ovipositor

Which structures in insects help detect chemicals?

Antennae, palps, legs, and mouthparts equipped with sensilla

What are the two types of insect chemoreceptors?

1) Olfactory (smell) 2) Gustatory (taste)

What are odorants?

Chemical molecules that trigger olfactory receptor activation

How do insect olfactory receptors work?

They are ligand-gated ion channels that respond to odorants

What does “response profile” mean in olfactory receptors?

Sensitivity of receptors to specific odorants (e.g., mosquitoes to certain chemicals)

Where are olfactory receptors located in fruit flies?

In different sensilla types: basiconic, trichoid, coeloconic

Where do olfactory signals go in the insect brain?

To the antennal lobe, where processing begins

What happens to signals from the same olfactory receptor type?

They converge into specific glomeruli to improve odor discrimination

What is the “odor code”?

Each odor activates a unique set of glomeruli, forming an odor-specific pattern

How do insect and human olfactory systems differ?

Insects use ionotropic channels; humans use GPCRs. Both serve similar functions

Where are human olfactory receptors located?

In the nasal cavity; signals are processed in the olfactory bulb

What type of receptors are used in human smell?

GPCRs that trigger intracellular signaling when bound by odorants

What taste categories do humans have?

Sweet, salty, sour, bitter, umami

How are taste and behavior linked in insects?

Sweet = acceptance, Bitter = rejection; insect gustatory receptors work like olfactory receptors

How do neuromuscular systems differ between insects and vertebrates?

Insect motor neurons use glutamate (excitatory) and GABA (inhibitory), with multiterminal, polyneuronal innervation, while vertebrates use acetylcholine and have one excitatory axon per muscle fiber

What are visceral muscles in insects, and what is their function?

Visceral muscles in insects surround internal organs and control involuntary actions like digestion and circulation

What are skeletal muscles in insects, and how do they function?

Skeletal muscles attach to both ends of the exoskeleton and enable movement by contracting and pulling body parts

What distinguishes insect flight muscles from other skeletal muscles?

Flight muscles can be synchronous (1 nerve signal = 1 contraction) or asynchronous (1 nerve signal = many contractions), allowing for rapid wing beats in species like flies

What is the basic cellular structure of an insect muscle?

It is a single, multinucleate cell made of repeating sarcomeres composed of thick and thin filaments (myosin and actin)

What is the role of myosin in insect muscle contraction?

Myosin forms the thick filament and uses ATP to pull on actin (thin filament), generating the force required for muscle contraction

What does actin do during muscle contraction?

Actin forms the thin filament and serves as a track for myosin to pull on, causing the muscle fiber to shorten

How does muscle contraction occur at the molecular level?

Motor neurons trigger calcium release, allowing myosin to bind actin and contract the muscle

How do vertebrate motor neurons innervate muscle fibers?

They are cholinergic (use acetylcholine), have one axon per muscle fiber, and all signals are excitatory

How do insect motor neurons differ in innervation compared to vertebrates?

Insects use both excitatory (glutamate) and inhibitory (GABA) signals, have multiple axon terminals per fiber (multiterminal), and receive input from multiple neurons (polyneuronal)

What are synchronous insect muscles, and how do they function?

These muscles contract once per neural impulse, commonly seen in insects with slower wingbeat frequencies

What are asynchronous insect muscles, and what is their advantage?

These muscles contract multiple times per single nerve impulse, allowing high-frequency movements like rapid wingbeats in flies and bees

How do physiological systems influence insect behavior?

Insect behavior is shaped by internal states and environment, integrated by the nervous and endocrine systems

What is an insect innate stimulus (releaser), and what does it trigger?

A releaser is an external stimulus that activates a specific neural circuit, triggering an innate behavioral response

What is a release hormone in insect behavior?

A release hormone is produced by the nervous system in response to a stimulus and directly triggers a specific behavior

What is a modifier hormone in insect behavior?

A modifier hormone alters how insects respond to stimuli, influencing motivation or intensity of behaviors without directly initiating them

What is the general pathway from stimulus to behavior in insects?

Stimulus (Releaser) → Nervous system processing → Motor response (Behavior), sometimes modulated by hormones

What is a reflex in insect behavior?

A reflex is a simple innate behavior mediated by a reflex arc (sensory neuron → interneuron → motor neuron), such as startle or escape responses

What are kinesis and taxis?

Kinesis is a random movement in response to stimulus intensity, while taxis is directed movement toward or away from a stimulus

Name some complex innate behaviors in insects

Hatching, ecdysis, eclosion, feeding, grooming, reproductive behaviors (courtship, mating, egg-laying), and social behaviors (swarming, aggression)

What is the Gal4/UAS system used for in insect physiology?

It’s a genetic tool that allows researchers to activate or silence specific genes or neurons in insects to study behavior

How do ion channels like Kir2.1 affect insect neurons?

Kir2.1 hyperpolarizes neurons, reducing their excitability and suppressing behavior linked to those neurons