Transcript Lecture 13

The basic building blocks of …any fast biological system are an
engine (horse’s muscles), an amplifier (the pole) and a tool, in this
case the horse.
Dark Side of the Horse by Samson
Lecture 13
Elastic mechanisms and power amplification
resilin in locusts
Resilin is a protein; it is protein chains joined by covalent bonds cross-linking between
tyrosine amino acids (residues).
“this amino acid lacks a side chain and is nonpolar, characteristics that prevent the
formation of the sort of electrostatic bonds that would otherwise constrain the shape
of the molecule. Freedom from constraint allow formation of random-coil chains.”
Cord-like tangle of variable topography
50% water in its natural state
From Wikki
Young’s modulus
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Young’s modulus is an index of the stiffness of a material
E = change in stress/change in strain
Stiff materials have a high Young’s modulus and rubbery materials have a low
Young’s modulus
Coral skeleton 60000
Mollusc nacre 30000
Abductin 4
Resilin 1.8 INSECT RUBBER
See Vogel for a table of values: p. 298, 2nd edition Comparative
Biomechanics
Locust flight {Source: R.E. Snodgrass The thoracic mechanism of a
grasshopper, and its antecedents. Smithsonian Miscellaneous Collections 82,
pp. 111. } [This reference is given just for completeness; it is not something you
need to obtain and read, but it is the source of much of the information here
and in the lab.]
Locusts are strong fliers. The flight-powering muscles of the locust are indirect:
meaning they don’t insert on the wings. They have their effect upon the wings by
distorting the pterothorax and by tergal tipping of the second axillary. (The pterothorax
is the flight tagma (just segments 2 & 3, not the prothorax.) There are two antagonistic
muscle sets: longitudinals (downstroke) and tergosternals (upstroke).
Sct2 is the scutum of the
second segment of the
thorax; scutum is the name
given to a part of the
tergum, as is Scl2 which is
scutellum.
Muscle 81, e.g., is a
longitudinal flight muscle
pulling between phragma 1
and 2, 112 is the same
pulling between phragma 2
and 3. These increase the
arching of the terga
creating forces at the wing
bases (PWP & 2nd axillary
sclerite).
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The longitudinals are situated high up in the pterothorax. Partially obscured behind
them, arrayed against the pleuron, are the many tergosternals (83,84,89 etc.), running
between the sterna (S2,S3) and the terga (Sct2,Sct3). The axes of the tergosternals all
lean headward (the insect’s anterior is to the left). Notice how the upper end of the
tergosternals insert on the terga where their contraction can reduce the convexity of
this region. Reducing tergal convexity is associated with elevation of the wings.
More diagramatic views: Snodgrass drew the phragmata (Aph anterior phragma, Pph posterior
phragma) of Fig. 129 purposely distorted, so as to show their interconnecting longitudinal
muscles both ahead and behind: notice the critical placing of the second axillary, 2Ax, atop the
pleural wing process, WP.
contraction of the longitudinals wings go down
contraction of the tergosternals wings go up
Notice
pleural
And sternal
apophyses in
background
Euler buckling
dorsal
Function of the pleural ridge
ventral
“The addition of flanges stabilizes
against buckling since it increases
the effective thickness of the plate
in selected areas effectively
dividing the plate into shorter
lengths.”
Tergosternals contract and forces would tend to buckle the pleuron; the
pleural ridge stiffens the side between the wing base and the coxa.
Function of the pleurosternal muscles: even more stiffness
Imparted to the thoracic sides (pleura): and VARIABLE.
The wing is a outfolding of cuticle, double layered. Basally are 4 axillary sclerites and 2
median plates (m, m’) linking the basal/proximal ends of the veins (costa, subcosta,
radius, median) to the margins of the tergum. The tergum is to the left (not shown).
The third axillary serves in flexing the wing over the back when the insect is not flying.
Downstroke and upstroke of wing and the anatomy.
basilares2
2nd
axillary
subalare2
PWP2
Seen here in dissection, the heavily sclerotized pleural wing process with the second
axillary that contacts it above. See also the basilare, 1Ba2 per Snodgrass, involved in wing
pronation and upstroke and primitively a leg muscle, but now co-opted for flight.
Seen from below the wing, some of the same veins (Sc) and axillary sclerites appear, the 2nd
axillary 2Ax, is crucial; it is concave and sits atop the wing process – providing the fulcrum of
wing up and down movement.
Explanation of
how the prealar arm
stores elastic
energy: basilare
muscle pulls on
basilare sclerite which
pulls on the ligament,
stretching the prealar
arm resilin. The two
resilin springs, prealar
arm of phragma 1 and
hinge at top of PWP
[in red], store energy
by tension during the
upstroke, energy
derived from the
flight muscles.
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Shape change in the
tergum (reduced
convexity centrally,
with outward and
downward movement
at the tergal margins)
is brought about by
the tergosternals. So
over a very shortdistance a downward
force acts on the near
end of the 2nd axillary
(red arrow); this
rotates the proximal
end of the 2nd axillary
around the pleural
wing process (PWP)
and raises the wing
that is linked to the
axillary.
Elastic energy from
the upstroke is stored
in the wing hinge
resilin (as well as the
prealar arm [not
shown]).
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During the
downstroke energy
returns from the wing
hinge and prealar arm
contributing to the
rebound of the wing.
The longitiudinals,
antagonists of the
tergosternals are now
changing the shape of
the tergum back to
more convex and the
force acting on the
proximal 2nd axillary is
upward (red arrow).
scutellum
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scutum
Picture by Piotr Naskrecki : The Smaller Majority a highly recommended blog for
remarkable photos and fascinating natural history.
Order Diptera (includes all the flies): one wing pair only, greatly reduced pro and
metathorax; the hindwings have become sensory flight structures called halteres; the
mechanism of fly flight has been extensively studied and early models included the now
discredited ‘click mechanism’..
The non-click mechanism of true flies
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A wing in the Order Diptera is, still like that of the locust, a first class lever with a
short force arm: its up and down movements are effected indirectly by
longitudinal and dorsoventral antagonists. As in the locust the flight muscles
change the shape of the tergum of the thorax. But because of its more intricate
form in flies (scutellum, scutellar lever, scutellar shelf etc.) the tergum distorts
topographically in different directions during the wingstroke cycle.
Consider just the downstroke as brought about by contraction of the [dorsally
placed] longitudnals, running from anterior to posterior phragmata.
PLEURO
The longitudinals (green)
when they contract
reshape the tergum
(scutum , scutellum are
regions within the
tergum). The scutum
bows upward in the
longitudinal plane; the
same longitudinal
muscle contraction tips
the scutellar lever: the
scutellum goes down
(rear red arrow) while
the lever pushes up at
the wing base, (anterior
red arrow). The
distortion of the scutum
also creates lateral
forces at the wing base
acting outward.
Scutellar lever is a ‘throw-rod’ for changing gears
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The several small axillary sclerites embedded in the membrane at the wingbase
can be mentally modelled as ‘gears’ ,the scutellar lever as a ‘gear shift’. Of course
these gears are not little wheels with teeth; but they are tiny intricately shaped
pieces of cuticle with projections and recesses, capable of moving upon each other
into a wing-up position or a wing-down position . Make a fist and imagine your
knuckles as if they were axillary sclerite projections and recesses. There are two
positions of axillary sclerite engagement, one coinciding with wings up and one
with wings down. The scutellar lever tipping (rocking) with each antagonist
contribution from the flight muscles is pushing the 1st and 2nd axillaries into and
out of either the up or the down position. In other words the shape change in the
thoracic ‘box’, coming about because of the contraction of the muscles, is so
designed as to ‘gear’ the wings for down or up.
Though they are remote from
the wing, small pleurosternal
muscles play a role in changing
wingstroke power. Internally
from the floor (sternum) and
from the side (pleuron) of the
thorax arise cuticular
projections: pleural apophysis
and sternal apophysis (see
diagram B). These projections
are apodemes, part of the
exoskeleton , and they are
joined by tiny pleurosternal
muscles. The outward lateral
forces created at the wingbase
by tergal distortion arising from
longitudinal muscle contraction
– these lateral forces can be
offset by the pleurosternals.
That is, the pleurosternals can
stiffen the pleuron so its
bending stores more elasticity
and gives a more powerful
downstroke.
FULCRUM
CHANGE
RADIAL
Fulcrum starts as second
STOP
axillary atop pleural wing
process (PWP).
Just past half-way in
downstroke the radial stop
on underside of ScR vein
comes to rest on PWP and
2nd axillary (violet) ceases to
be part of the fulcrum; this
will improve the force arm
length slightly. The first
axillary pries up on
parascutal shelf (C),
triggering dorsoventral
(tergosternal) muscles
myogenically.
Myogenic muscle contractions and recoil elasticity
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After the radial stop rests on the PWP, the base of the ScR pries the
first axillary up upon the parascutal shelf (Diagram C). This lifts the
scutum a very small bit which stretches the tergosternals slightly ,
stimulating their contraction. These flight muscles are fibrillary
myogenic (not neurogenic), -- antagonists working back and forth to
stimulate each other’s contraction -- without motor neuron activity once
started. This flying machine is so designed that the contraction of one
antagonist power muscle slightly stretches the other.
Three hundred strokes per second is not high among mosquitoes.
Wingstroke rates can occur up to beyond 1000 per second: in some
midges this is the flight tone.
Elasticity via cuticle in this system: as the wing moves down, there is a
bending of both the pleura (if the pleurosternals are contracted) and of
the veins of the wing. Strain energy is stored in this bending: it is
returned on the upstroke, contributing to it as a recoil. The wing doesn’t
start up just on the basis of dorsoventral contraction, it bounces up as
the distorted thoracic pleura and ScR returns to its prestressed state. In
Patek’s terms the muscles are engine, the pleuron and veins are
amplifier powering the wing.
The end of locomotion and the start of a section on feeding
Concentrating particulate food
Filter feeding: making a mouthful efficiently
‘Lophophores’
There are many animals with structures that function to filter small
organisms and organic tissues (the result of predation) out of seawater or
sediment. These structures concentrate the ‘organics’ into efficient food
portions separating them from inorganics (e.g., silt). Cilia and mucus and
slits in their pharynx or a whorl of branching mouth-surrounding
tentacles are filter feeding structures. For some animals flow patterns are
sufficient to create separation and mucus is not involved: rakers on fish
gills, a series of beating crustacean limbs or a mouthful of whale baleen.
For many there is a close association between locomotion and feeding:
either a current must be created or the feeding animal must move
through the water. Large filters mean large surface areas exposed to
passing water and this gives the opportunity for diffusion: gas exchange
and Nitrogen excretion are often associated with filter feeding structures.
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In no particular order the following is a list of some of the many
animals concentrating particulate matter as food by filtering: bivalves
(Mollusca) using their gills, sea squirts (Urochordata), amphioxus
(Cephalochordata), Chaetopterus, Arenicola [lugworm] (Annelida), fan
worms (Annelida), blackfly larvae (Simuliidae), mosquito larvae (Culicidae),
commatulids, crinoids (Echinodermata), rotifers (Rotifera), lophophorates
(Bryozoa), sponges (Porifera), barnacles, brine shrimp, Daphnia
(Arthropoda), sea cucumbers (Holothuroidea, Echinodermata),
Branchiopoda, Artemia (Crustacea); ram-feeding fishes: paddlefish,
anchovies, herring, sardines, mackerel; ram-feeding sharks: manta ray,
basking shark, whale shark Rhincodon; suction feeders: dabbling ducks,
flamingoes, tadpoles, lamprey larvae; intermittent ram feeder: rorqual
whale [krill, baleen whale], mole crab (Decapoda)...etc.
Baleen whales filter the crustacean,
krill.
Krill filters diatoms. Both the whale and
its food are filter feeders.
Flipper bumps:
function relates to
filter feeding: herding
krill by tighter turns;
bumps delay stall*.
Diatom: unicellular
alga with a silicate
covering
*See van Nierop E.A.
2008
Whale sharks are the biggest of all fish species, growing >12 m
long, yet like the rorqual whales, they feed on relatively tiny,
vastly abundant organisms they filter from seawater.
Is there some reason why the largest
mammal and the largest fish are
particulate feeders? Does relative
size make filtering more physically
effective?
Arenicola, lugworm: ocean flats tidal detritus feeder, Annelida
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Malcolm Storey
Tide sweeps in
carrying detritus
that
accumulates on
the bottom.
Worm ingests
mud/sand,
taking from
shaft of
‘puddled’
inorganic
substrate; egests
castings onto
the surface at
other end of
burrow.
Not really filtering?
Coelomic pressure everts
pharynx for both burrowing
and feeding in lugworm:
hydraulic eversion.
Castings from a colony of lugworms on the seacoast
Like the lugworm, earthworms eat dirt: i.e., they ingest dirt: but
they are not filtering (i.e., separating) food from dirt: they .
Earthworms exchanging sperm
Feeding on nematodes, protozoa, rotifers, bacteria, fungi by ingesting soil.
How does an earthworm separate the food from the dirt?