Lecture 17

Lecture 17
Suspension-feeding birds: duck & flamingo
Comparing the cicada and aphid clypeus
Gut tube adaptations: discontinuous feeders and crops, gizzards, shunts,
rumens, etc.
Ennos Roland 2012. Solid biomechanics. Princeton Univ. Press,
Princeton, Oxford.
Added to reserve list in library. A very good resource for
concepts you don’t understand or where you wish for more
For example see his Chapter 2 Biological Materials, Biological
Protein Rubbers, Resilin, Abductin, Elastin.
Chapter 1 deals with Newton’s laws, stress, strain, Young’s
Compliance is the inverse of stiffness; stiff materials have a high
Young’s modulus, compliant materials (like resilin) have a low
Young’s modulus.
p. 36 he deals with the prealar arm.
Mallard duck is a suspension-feeder: there
are rows of projections called lamellae on
the bill.
“…when the mouth is closed, the large
upper bill completely covers the lower
…and when the mouth is slightly ajar, the
adjacent lamellae of the upper and lower
bills can act together as a sieve.” They
must interdigitate. The tongue (hydrostat,
blood) powers this filter via swellings.
“…anterior swelling [drops] away from the
roof of the mouth when the tongue moves
forward, allowing water to enter the mouth
from the front. When the tongue is drawn
back, the front swelling presses against the
roof of the mouth [like a piston], forcing
the water backward and out the sides of
the bill through the lamellae.”
“… [a] rear swelling has
projections called lingual
scrapers on both sides; as
the tongue moves back and
forth these scrapers act to
dislodge food particles from
the lamellae and draw them
[back] to the oesophagus. In
mallard ducks, the tongue tip
moves forward about 11 mm
and then back again every 60
to 70 milliseconds. This rapid
oscillation moves the water at
high velocity, and so the
lamellae may capture food
particles by inertial
impaction as well as by
Inertial impaction:
Aerosol Impaction is the process in which
particles are removed from an air stream by
forcing the gases to make a sharp bend.
Particles above a certain size possess so much
momentum that they can not follow the air
stream and strike a collection surface which is
available for later analysis of mass and
composition. (Wikki)
Upside down: changes
In upper jaw to
improve its mobility
‘ultimate suspension-feeding bird’
The face of a flamingo is dominated by the
filter on its face.
Comparing frons (face) of
aphid and
Cicadidae or Cicadellidae
Sparky’s ice cream, Columbia Mo.
USDA, Clemson
Shape of a cicada’s face
is determined by a
cibarial pump; cicada is
a fluid feeder that needs
to create its own
pressures to suck sap.
Cibarial dilator muscles
contract, dropping internal
relative to external pressure:
this pressure differential
moves fluid up stylet bundle*.
*Stylets are modified mandibles, maxillae,
labium, elaborately lengthened and forming
collective tubes for sap transfer. The cicada
pictured is one of the 17-year ‘locusts’ that
emerges in large numbers: a periodical cicada.
Where a pump is needed, because
the fluid food is not itself under
pressure, a plant feeding insect
may evolve one: pharyngeal or
cibarial. Is this why cicadas, spittle
bugs etc. have such a dilated
Heads of aphid and cicada/spittlebug compared: cicadellids and
cicadids have a disproportionately large cibarial pump. Why?
Vascular plants, vascular tissue: phloem and xylem. Phloem is to the
outside in most vascular plants; just beneath the bark of a tree.
Phloem transports sap which contains sugars, the products of
photosynthesis, direction of flow can be up or down, depending on to
where the sugar is being transported.
Aphids feed on phloem and obtain so much sugar it becomes a waste
The aphid is dealing with a food which it concentrates in order to filter
out food substance other than sugars. For this purpose it has a shunt
in its gut.
Xylem is vascular tissue that has always an upward directional flow and
is associated with transpiration. It is mostly dead cells.
Does xylem have sugars (when one taps a maple is it the xylem that is
tapped? Is it worth feeding on?) Do cicadas feed on xylem; is xylem
mostly at lower pressures than phloem, creating the need for a strong
cibarial pump?
A problem?
Aphid mouthparts (mandibles,
maxillae, labrum and labium) are
greatly lengthened, the first two
drawn out into a long slender
‘stylet bundle’, the labrum and
labium supporting the bundle
base against the head.
Each stylet is moved by retractor
and protractor muscles situated in
the head. The insect has channels
within the adpressed maxillae,
one to convey phloem sap up and
in and one to carry saliva
downward to lubricate bundle
penetration with glandular
secretion (i.e., aphid spit).
Two grooves on the inner face of
each maxillary stylet (blue) make
up the two halves of a salivary
canal and a food canal.
Working its way down through the plant
tissue, the stylet bundle gains support
from the cellulose cell walls like a ‘worm’
used to clear blocked drains; confined
laterally it cannot bend very far before
being pushed forward; the insect takes
many minutes (up to an hour) to reach
the phloem and begin feeding.
Phloem pressure pushes the sap up the
maxillary food canal; apparently no need to
pump/suck the fluid: note small head and
thorax suggesting absence of a pump.
section stylet
Rosy Apple Aphid with stylets inserted in plant
Mandibular stylets (red) do the work of
piercing the plant tissue, a right is thrust out a
short distance (protracted) and penetrates
down; then the left pushed until its tip meets
that of the first; then the two maxillary stylets
are lowered together into the created space:
this is repeated between the walls of adjoining
plant cells until the pholoem bundle is
Aphids are used to collect
Plants in action
phloem sap samples. Top
photograph: a feeding aphid
with its stylet embedded in
a sieve tube (phloem). [scl,
sclerenchyma; st, stylets; x,
xylem; p, phloem. Note the
drop of ‘honeydew’ being
of ‘honey dew’
excreted from the aphid’s
(a) to (e) show stylet cutting
(microcautery) at about 3-5
s intervals (a to d) followed
by a two-minute interval
(d,e) where exudate
accumulates. The stylet has
just been cut in (b); droplets
of hemolymph (aphid origin)
are visible in (b) and (c);
once the aphid moves to
one side the first exudate
appears (d), and within
minutes a droplet (e) is
available for microanalysis.
Winged aphids can appear in populations and are the basis
of dispersal
The aphid needs to filter phloem and perhaps because of the
pressure needs to secure a quiet backwater in its gut for
secretion of enzymes and absorption of the products of
digestion. The pressure pushes the fluid through at a high
rate. Its gut loops back on itself and then is turned in
‘switchbacks’ overtop of the anterior midgut. This ‘filter
chamber’ also functions a shunt: it allows for certain portions
of the fluid to bypass the posterior midgut; through differential
absorption the two overlain gut walls filter the wanted out of
the unwanted.
Gut tube adaptations
• Inferring function from gross form may be more intuitive with guts
than other body parts. Suppose you’re an animal with no teeth
(because you’re a bird) and you also need a place to hold food while
you travel (because you’ve got wings instead of hands, because
you’re a bird), and you’ve got a lot of food available all at once?
• You need to evolve a sac-like gut region with progress regulated by
a sphincter muscle valve: need a crop or a pharynx .
• The gut of animals is a long tube, with regions specialized for
different assembly-line functions: regions specialized to: store, grind,
churn, ferment, secrete enzymes and resorb digestive products and
water, ultimately to accumulate and egest waste*.
Gut diverticulae and storage: sacculate crop of leech: extreme
downtime between blood feedings: adaptiveness of a crop.
The leech (Annelida) has a disproportionately
large crop in which it stores blood; this crop
is comprised of many blindly ending lateral
sacs that increase its capacity. Leeches feed
on a food that is ready to digest so no teeth
are required to ‘chew’ it. But the leech does
have teeth to make the entry wound in its
Diagram from sharon-taxonomy on the web
McGill Office Science & Society
Discontinuous feeding
(Culicidae): its
crop rleates to
the function of
the insect
Why don’t aphids
have a crop?
Another highly discontinuous fluid
feeder, one finding a blood source
only on occasion, the mosquito
must often get all its food intake
from just one feeding event. It uses
piercing and sucking mouthparts
elongated into a ‘straw’, halfgrooved appendages adpressed to
make composite channels for fluid
feeding (just like the aphid).
This insect takes in a large quantity
of blood and has to store it for later
digestion. For this it needs a crop.
Why no dilated face?
Diverticulae of the gut tube arise in
the thorax; but the thorax is a
locomotory tagma, its volume mostly
occupied by flight muscle. No room for
blood storage in the thorax. On the
other hand the abdomen’s telescoped
segments are designed for expansion.
Need to prevent blood coagulation during storage.
Some mosquitoes
feed on frog blood.
• So the main crop (red) extends
into and occupies the mosquito
abdomen. It receives the blood as
ingested (a valve shuts off the
midgut) and the abdomen
expands greatly. So one of the
abdomen’s functions as a tagma is
illustrated: allowing expansion to
accomodate food intake.
Ennos p. 80: chapter on polymer composite materials
The problem of using vascular plants as food is cell walls and lignification.
[Similarity of plant cell walls to arthropod cuticle)
“Like cuticle, the plant cell wall is a composite of fibres of a straight-chain sugar” –
cellulose fibrils. The cellulose “occurs within a matrix made of branched
hemicellulose molecules.”
“The mechanical properties of the cell-wall material is strikingly similar to that of
cuticle.” “The high compliance of the matrix allows developing cells to stretch
their cell wall using turgor pressure, just as insects stretch their skeletons at molt.”
“Another similarity of cell walls to insect cuticle is the way that many of them are
stiffened and strengthened by the process of lignification , which is very similar to
the process of sclerotization. During lignification the complex polyphenol
molecule lignin is incorporated into the cell wall…resulting in cell-wall material that
is stiffer and stronger [with]…a lower breaking strain.
The cell wall of plants becomes a major problem for herbivores in getting at the
cell content as food.
Bird gizzard
Rocking T Ranch
• An organ thickly invested
with muscle that requires
ingested gravel to ‘mill’ the
food into smaller particles.
Notice the peculiar form of
the lining tissue.
And birds also have a crop:
useful for storage: it takes
more time to digest than
Teeth specialized with a high
crown for grinding. Major tooth
1) enamel, shinny hard thin layer over the tooth surface: almost completely
inorganic. “Two-thirds of its substance consists, as seen in mammals, of
long prisms of calcium phosphate, arranged with their axes at right angles to
the surface...” (Romer); 2) dentine, softer, wears more easily, forms main
bulk of tooth. 3) cement. These 3 materials, differing in wear rates, keep
tooth from becoming smooth through wear
Grazing hoofed mammals have plant-wall chewing problems.
Hypsodont teeth: high-crowned, protrude well above the gum, creating length for
uneven wear during a lifetime of grazing (grasses with silica being an adaptation of
the plant to protect itself from such grazers). Ruminants and horses have
hypsodont dentition. The opposite condition is called brachydont. Hypsodont teeth
may also be selenodont (see next slide). A cow’s teeth continue to grow through
prehistoric gazelle
Greece Museum Paleontology Geology
Diastema: tooth series separation;
function in the horse? Lets tongue out?

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