1

RespirationDiet Specializations

1. Respiratory systemsa. Anatomyb. Air movementsc. Gas exchanged. Respiratory pigments?!2. Digestive systemsa. Mouthparts and dietb. Major gut divisions (structure and

function for each section)c. Integrating digestive and excretory

systems for water balance

Openings leads to system of pipes General Organization

• Longitudinal trunks: lateral dorsal, ventral

• Cross wise tracheae:dorsal, ventral visceral

Major branches extend up, down and in

spiracles –openings to the

respiratory system

2

spiracles can be

• permanently open• permanently closed• able to open and close• respond to neural input or directly to CO2

Tracheal structure

• lined with cuticle• branch and join• finest branches

are intracellular

tracheal epithelial cells

• cuticle shed at molt

• taenidia for strength

Tracheal structure

• Tissue dissolved away - slinky like structure obvious

• must withstand negative pressure

tracheoles and tracheole cells

• tracheoles keepcuticle at molt

• intracellular

tracheoles

• in active tissue, tracheoles reach near mitochondria

• atmosphere oxygen diffuses into tissue

• CO2 released from tissue into tracheole

3

Systems with air sacs• taenidia reduced or absent • collapse under pressure• important in ventilation – forced air

movements• NOT lungs

open (to the air)respiratory systems

closed respiratory systems How can a closed respiratory system work??

• it’s the physics

Diffusion of oxygen• oxygen in air diffuses >100,000 times faster

than in water or tissues• Carbon dioxide diffuses 10,000 times faster• so ... • faster from

spiracle to tracheole

• than from tracheole to mitochondria

Diffusion of oxygen

4

Gas Exchange

• Ventilation • Internal air movement • Diffusion

ventilation

• at rest, most of the time all spiracles closed• air goes in and out of a spiracle- tidal flow • opening and closing spiracles at different

times, with ventilation, can create flow in one direction

resting ventilation, examplehyperventilation - time ‘all closed’

is reduced - continuous

in flight, all spiracles are used

inspiration

expiration

Internal compression

5

What is going on with actual gas exchange?

• development of equipment that can measure very small changes in gas levels allows study of this question

Gas Exchange with Working Spiracles

• research dependent on technical equipment that can measure very small changes in gas concentrations in tiny spaces

Gibbs, A. G. et al. J Exp Biol 2004;207:3477-3482

Recordings of CO2 release (Ai-Ci) and water loss

Three general patterns of respiration in insects

discontinuous disc., no long closed period

continuous

(discontinuous gas exchange cycle = DGEC)

• in resting insects (easiest to study)• measurements have shown that gas

exchange occurs in distinct bursts• especially extreme in pupae

Cecropia pupa

• takes a breath every 8 hours

3 spiracle phases

• Closed• Flutter• Fully open

6

• end of open phase –gradient favors diffusion out of CO2, H2O

• spiracle closed, CO2 build up, no change in H20

• spiracle opens –gradient for CO2 flow out high, H20 always the same

Start with Closed Phase• pO2 falls• Pressure falls• Flutter begins• Pressure equalizes• Build up of CO2

triggers spiracle to open

• O2 triggers closurepO2

pressure

CO2 release

What is the functional significance of DGE?

• Reduce respiratory water loss?• Protection from toxic oxygen?

Manipulate oxygen levels

• Red line is oxygen level in atmosphere

• Green lines are CO2 release

• Blue line is the O2 level inside tracheae

2005 Nature 433:516

At low oxygen

• Oxygen levels constant

• Spiracles open often to allow more oxygen to get in

• Frequent small releases of CO2

At high oxygen

• Spiracles rarely open

• Oxygen level trachea the same as in low oxygen conditions

7

Oxygen nicely regulated!

• oxygen levels (PO2) are constant regardless of oxygen level

Oxygen is a poison!• When photosynthesis evolved, atmosphere

started accumulating oxygen • Water is split (CO2+H20=CH2+O2), • Oxygen attacks chemical bonds, very

corrosive• New systems had to evolve to deal with it• Think how corrosive pure oxygen is to us,

even now• Think how antiOXIDANTS are good for you

• Using DGE, insects reduce gas exchange to reduce toxic effect of oxygen that is not being used quickly

• Cycle disappears in active, flying insects. Oxygen is being used quickly

• Insect respiratory system functions most efficiently at high levels of oxygen consumption

What is the functional significance of DGE?

• Reduce respiratory water loss? YES?• Protection from toxic oxygen? YES

Respiratory pigments?

8

HEMOCYANIN ArcheognathaThysanuraOrthopteraDermapteraIsoptera

Hemocyanin• common in spiders, Crustacea,

mollusks• copper carries oxygen, gives it a blue

color• previously believed

insects didn’t need it because they live in a relatively high oxygen environment

Hemocyanin in insects

• Perla – a stonefly, carries functional hemocyanin in its blood

• In the other groups, it is found in tissue cells

Hemoglobin

• larval Chironomus -midge

• Gasterophilus - a dipteran parasite

HEMOGLOBIHemipteraColeopteraLepidopteraDipteraHymenoptera

Hemoglobin in insects

• in hemolymph of Chironomus

9

Chironomus

• larval chironomids are called "blood worms"

• they contain a small hemoglobin• with high affinity for oxygen• allows them to extract oxygen from

water in low oxygen environments• the only insect (so far) that has Hb in its

blood

Hemoglobin in Drosophila and Apis

Found in tissues, not in hemolymph

J. Biol. Chem. 277(32):29012 (2002)

Hemoglobin in Drosophila

A. very early embryoB. yolk sacC,D. fat bodyE. tracheal cellsADULTSF. tracheal cellsG. fat body cellsH. late oogenesis

J. Biol. Chem. 277(32):29012 (2002)

Diffusion of oxygen

remember that diffusion of oxygen through tissue between the tracheole and mitochondria is slow

Hemoglobin

Location in tracheoles may allow steady oxygen flow to mitochondria when oxygen content of air varies?

Non-toxic store of oxygen

• relationship of INSECT HEMOCYANINS to other arthropod hemocyanins

• higher insects have lost them• (have a new function!)

10

Did hemocyanins vanish in most insects?

• No, they morphed into related proteins called hexamerins, or storage proteins

• Allows insects to store amino acids!

storage proteins

Food Processing

I. basic equipment + diversityII. designs for floods and droughts

Insect diets vary widely

• Animals, plants• Solids, liquids• Wide range of food types – generalists,

scavengers• Narrow range of food types – specialists• Mouthparts, gut structure…. vary widely

and reflect diet

11

consider my head and its mouthparts

• labrum• mandible• maxillae• labium

Hypopharynx• labrum• mandibles• maxillae• labium

12

mouthparts

• any of the parts can be modified• modified parts work together to make a

mouth that functions completely differently from other plans

Your basic gut

FOREGUT MIDGUT HINDGUT

foregut - general features

• cuticle lined• overall

unsclerotized• but can have

sclerotized spines

foregut regions

• pharynx• esophagus• crop• proventriculus

grasshopper pharynx-crop

• pharynx especially has muscles

• muscles give the ability to PUMP

13

pharyngeal pump -Lepidoptera

• Lepidoptera

pharyngeal pump -plant fluid feeds

foregut regions

• pharynx• esophagus• crop• proventriculus

foregut regions

• pharynx• esophagus• crop• proventriculus

crop

• storage• extensible part

of gut• Diptera and

Lepidoptera have permanent sac

The capacity of the CROPcan be enormous.

Quality of cuticle (impermeability) important in ability to store

Honeypot ants

14

foregut regions along its length

• pharynx• esophagus• crop• proventriculus

proventriculus

• anterior part of valve between foregut and midgut

• variable form

proventricular spines

• orthopteroidinsects

• push and tear food

• good species specific characters

midgut

Your basic gut

FOREGUT MIDGUT HINDGUT

Midgut - general features

• = ventriculus• NOT lined with cuticle• gastric caeca• secretes enzymes• absorbs nutrients• secretes peritrophic

envelope

Caeca

• increase absorptive surface area?

• often contain micro-organisms, possible symbionts

15

Midgut

• secretes peritrophicenvelope/matrix

• type I – forms over surface of midgut

• type 2 – secreted anteriorly

peritrophic envelope

• forms lining for midgut

• found in most insects but not most Hemiptera

• can form in response to one food (blood) but not another (nectar)

function of the peritrophic envelope?

1. mechanical barrier from abrasion, pathogens, enzymes

2. compartmentalizes digestion for greater efficiency

3. biochemical barrier neutralizing toxins

Composition of the matrix

• chitin fibrils linked by proteins• glycans fill spaces• properties of matrix

depend on specific ion content and pH

separate lumen into two spaces

• this allows compartmentalization of enzyme activity for different materials

• more efficient absorption as digested material moves into space next to gut wall

Insect counter defense?

• Plants have defenses against insects• One strategy is to contain compounds

that will cause free radicals to form in insect herbivores

• Many plants contain enough iron to trigger free radical formation collected the peritrophic envelopes

16

The Experiment

• feed caterpillars artificial diet with different amounts of iron

• excreted peritrophic envelope contained the iron

• = PM scavenges iron

Does this protect the insect when radical producing

compounds are present? • add tannins, different iron levels• measure damage• =total protection!

What happens when you repeat experiment and

remove PM?• tannin and iron• add a chemical that disrupts

membrane• = damage when chemical

added• = it really is the PM that is

providing protection

More new protective abilities for PM

• Heliothis virescens (tobacco budworm) -protects against baculovirus infection

• Aedes aegypti – PM protein binds heme(iron)

Midgut subdivisions

Hemiptera often have midgut subdivided into several specialized regions

Midgut subdivisions

important for elimination of water and for housing micro-organisms

17

hindgut - general features• ileum, colon, rectum• pyloric valve

between hindgut and midgut

• Malpighian tubules (kidney tubes) attach below valve -great landmark

• lined with cuticle• very permeable

hindgut

• symbionts are often housed somewhere in the hindgut

• features to provide retention of these microbes

How do insects obtain water?

• in their food

Specialized diets with water imbalance

• blood• plant fluids• flour, grain

• short term surplus • constant surplus• constant deficit

Dealing with imbalance requires integrating digestive system with excretory system

Machinery for balancing water, ions

• malpighian tubules • digestive system

basic structure of malpighian tubules

1) attachment site2) cross-section

structure

18

Rhodnius prolixus

• short term surplus• feeds ~ once in 6

months• huge meal• must get rid of

water quickly so it can go hide

• kidneys (MTs) go to work

blood feeders• short term surpluses • hormonal activation of tubule to

increase activity• ions pumped in, water follows

Shortage of water Digestive system helps in water recovery

• moves water/ions from food to blood• recovering water/ions in urine• water recovery VERY important

rectal pads• pads of transporting cells• good tracheal supply indicates

metabolic activity• water and ions can be selectively

recovered

using malpighian tubules + gut to recover water

cryptonephridial arrangement