Insect Physiology prelim 2

CT_min

Lowest thermal limit

CT_max

Highest thermal limit

T_opt

Optimal temperature

Thermal safety margin

distance between T_opt and CT_max

T_br

width of thermal performance curve at ½ T_opt

Ectotherms

generate no meaningful internal heat

Endotherms

generate significant internal heat

Poikilotherms

do not keep body temp stable

Homeotherms

keep body temperature stable

Sources of heat

Sunlight, infrared radiation from objects

Sources of lost heat

IR put off by organism, metabolism, evaporation, conduction

Q₁₀

efficiency increase when temp changes by 10 degrees C

Q₁₀ = (R₂/R₁)^ΔT

Jensen’s inequality

With increasing temperature, ion diffusion rate increases linearly but pump rate increases exponentially

V_max

maximum rate of rxn (enzymes)

K_m

substrate concentration at ½ V_max

Arrhenius plot

X axis: 1/T

Y axis: log(rxn rate)

slope: activation energy

steeper slope = more thermally sensitive

How to change enzyme effectiveness

Change [substrate] — uncommon, [substrate] usually kept near K_m

Change “effective” [enzyme] — localize enzyme concentration where needed

Change enzyme-environment interactions — membrane phospholipids/environment, enzyme shape, charge, flexibility

Allosteric modification

Isozymes

Allosteric modification

A molecule binding to an enzyme somewhere other than the active site, causing a conformational change

Membrane pacemaker theory

that the composition of a cell membrane affects enzyme activity/metabolic rate

Homologs

Protein from genes that share a common ancestor

Orthologs

Proteins with a common gene in different species that share a function

Paralogs

proteins with similar functions produced by different but related genes in the same species

Analogs

proteins from unrelated genes with similar function

Effects of temperature on cell membranes

Cold — membrane loses fluidity (phosopholipid tails get closer)

Hot — phospholipid tails spread out, membrane fusion and/or hexagonal phase

Homeoviscous adaptation

maintaining the correct fluidity

Phosophilipid tail fluidity

Saturated tails less fluid, unsaturated tails more fluid

Longer tails less fluid, shorter tails more fluid

Supercooling point

the temperature at which a liquid, cooled below its freezing point without solidifying, spontaneously freezes due to spontaneous ice nucleation

Why does temperature briefly increase after the supercooling point

Heat of crystallization

Rapid cold-hardening

A rapid increase in cold tolerance in response to a pre-treatment at a low temperature

Freeze avoidance strategies

Stay supercooled, avoid actually freezing

Produce antifreeze proteins

Proteins that bind to ice nuclei and prevent growth

Remove ice nucleation points (e.g. empty gut)

Avoid contact with ice

Freeze tolerance

Survival of internal ice formation

Remove water from cells so that ice formation is external

Notable organism: Chymomyza costata

larvae can survive liquid nitrogen

Notable organism: Polypedilum vanderplanki

Anhydrobiotic larva can survive liquid nitrogen & boiling

Requires slow drying

Folds in half (minimizes surface area)

Notable organism: Exechia nugatoria

Fungus gnat with freeze-avoidant thorax and freeze-tolerant abdomen, dies when thorax freezes

Heat shock proteins

Chaperone proteins to help refold damaged proteins

Both constitutive & induced

Kleptohaematophagy

e.g. Rhodnius nymphs drinking blood from other engorged Rhodnius

Anhydrobiosis & shared traits

The ability to dry out completely and rehydrate again

Anydrobiotic organisms are

• small

• live in ephemeral aquatic habitats

• have little to no control over water loss

• accumulate small molecules & disordered proteins (e.g. LEA) to protect cells in the dry state

LEA proteins

Hydrophilic, disordered proteins that protect during dessication, act as chaperone proteins

Vitrification hypothesis

“glass” formation immobilizes solids in the cell, avoids ice crystal formation

See also alternative Water Replacement Hypothesis

Water replacement hypothesis

Trehalose, LEA proteins, etc replace water, maintaining the macromolecule conformations

See also alternative Vitrification Hypothesis

Reasons for dormancy

To avoid inclement weather

To synchronize timing to a resource or mating season

Diapause

A programmed state of arrest initiated in advance of stressful conditions

Aestivation — summer/hot version

Quiescence

A state of arrest initiated in response to stressful conditions

Facultative diapause usually triggered by ____

photoperiod

Why terminate diapause during winter?

Switch to quiescence to be able to wake up early if spring comes early

Behavioral fever

Combatting infection by moving to warmer areas

Illumina sequencing (parallel)

DNA cut into short strands, attached to flow cell, each base color-coded and an image taken of each layer of the plate

Shorter reads, fewer errors

Often placed on a long-read “scaffold”

PacBio sequencing (long)

A DNA fragment placed in a cell with a DNA polymerase molecule, as polymerase attaches each nucleotide the “pulse” given off is read

Longer reads, more errors

Often used as “scaffold” for short reads

Types of mutations

Loss of function

Gain of function

Conditional (insect-specific!)

Dominant-recessive

Forward vs Reverse genetics

Forward

phenotype → screen collection of a mutant → identify gene causing phenotype

unbiased but intensive & risky

Backwards

select gene → generate null mutant → phenotype

more direct but biased & limited

Benefits of Drosophila as genetic model

short generation time

simple genome w/ low copy number

no crossing over in males

How to tell where a gene is expressed

Staining — GFP tagging, immunofluorescence/immunostaining

How to tell how much a gene is expressed/produced

RT-qPCR: make copies of a gene via PCR, tag gene with fluorescence at each step, and record how many cycles it takes to reach a certain light threshold. More cycles = less gene

Blot: separate molecules by size (smaller travel further) in gel and then transfer to a membrane. Larger blot = more molecule

Blot types

Northern: RNA

Southern: DNA

Western: Protein

Reporter transgene

e.g. GFP

Transposable elements

Pieces of genes that float around the genome (~like a virus)

Properties can be hijacked to insert custom DNA

RNAi

method of downregulating genes

cleaves target mRNA strands

CRISPR-Cas9

Cleaves a target DNA strand and provides a template for repair

Gene drive

A gene inserted onto one chromosome cuts out its partner allele from the other chromosome and replaces it with itself. Thus all descendants carry the gene drive gene.

Relative [NA⁺], [K^-]

[NA⁺] higher outside neuron, [K^-] higher inside

Electrical synapse

Passes fast excitatory signals

Chemical synapse

Passes slower, excitatory or inhibitory signals. Transfers vessels of neurotransmitters.

Membrane voltage threshold

The threshold at which a neuron membrane is triggered to complete a full action potential

GABA

Inhibitory neurotransmitter

Opens Cl^- channels, decreasing membrane potential

Rhabdom

Dark-looking area caused by overlapping microvilli of photoreceptor cells

How is light detected?

Photo hits rhodopsin in the photoreceptor cell’s microvilli, causing a conformational change in the embedded vitamin A, inducing a messenger cascade

Typical insect photoreceptor sensitvity

Most have 3 types of photoreceptors with peaks in green, blue, and UV

Why might microvilli on the photoreceptor cells be all aligned?

To detect polarized light

e-vector

the plane in which a wave of light vibrates

Pseudopupil

Spot on the eye that looks black to the observer, composed of the ommatidia that are looking at the observer

Proprioception

Monitored by campaniform sensillae in the cuticle or by plates of hair (typically in asymmetrical socket) at/near joints

Cercus circuit

Directionally-specific groups of hairs on the cerci project axons to specific regions of the terminal ganglion, which send it acetylcholine excitatory signals. These signals are graded and decay over the length of the dendrite.

Lampyrid light circuit

Action potential in DUM neurons releases octopamine into cells, stimulating NO synthase and NO gas production, NO gas disables mitochondria which allows O₂ to pass, O₂ reacts with luciferin to produce light.

DUM neurons

Dorsal unpaired median neurons

Typically use octopamine

T-shaped

Sarcomere

smalles unit of muscle, composed of actin & myosin filaments between Z-discs

Myosin cycle

ATP binding causes myosin to release from the actin, ATP cleaving into ADP + Pi causes myosin head to ratchet forwards

Muscle regulatory proteins

Tropomyosin fiber blocks binding sites on actin filament

Troponin complexes, once bound to Ca²⁺, move tropomyosin out of the way

Where does Ca²⁺ in the muscle come from

Stored in the sarcoplasmic reticulum, released by action potential of transverse tubules

Polyneuronal innervation

A single muscle fiber may have multiple synapses, connected to different neurons. Each synapse/neuron may be a different type (e.g. some electrical, some chemical; some excitatory, some inhibitory, some modulatory) to allow finer control over the muscle.

Fast vs slow muscles

Fast muscles give large twitch for each spike, fatigue easily

Slow muscles give weak twitch, increasing twitch frequency increases force, rarely fatigue

Synchronous vs asynchronous muscle

Synchronous

smaller fibers, extensive sarcoplasmic reticulum, low intracellular Ca²⁺, 1:1 twitch:action potential

Asynchronous

larger fibers, less sarcoplasmic reticulum, high intracellular Ca²⁺, higher twitch:action potential ratio. Has evolved multiple times.

Neuron diameter

larger diameter = faster signal