March 14, 2013
Radula: snails eating algae
Fluid feeders: aphids
Pollen feeders: bees and bats
Weapons and other pointy things
Two-way table for comparisons
Structure
Ruminant
Ruminant
predator
eyes
lateralized
binocular
tail
flies
balance
foot
hoof
claws
leg
longer
long but
shorter
teeth
replaced by
growth
carnassials
canines
ears
moveable
pinnae
moveable
pinnae
gut
4chambered
stomach
1chambered
stomach
?
Excluding seeds and fruits
herbivory on green tissue of
plants is characteristic of three
large groups of animals:
gastropod molluscs, Orthoptera
(grasshoppers and allies) and
ruminant mammals.
In the gut wall, just behind the mouth of a
gastropod, recessed, there is a skeletal
plate the odontophore; it acts as backing to
a ribbon of keratinous teeth called the
radula. Antagonistic protractor and retractor
muscles contract alternately to pull the
radula to and fro across the surface of the
odontophore. This organ is a machine for
rasping algae off substrate. The
odontophore can be shifted into various
positions by its own set of muscles and
protruded far out through the mollusc’s
mouth. So it can be applied against
substratum (rocks, coral heads, aquarium
glass) coated with algae.
Teeth of the radula of
gastropods are species
diagnostic: why should the
teeth be this specific? Why
doesn’t selection converge on
the single most efficient form of
rasping tooth?
You can see a snail’s radula as it
rasps off alga from the glass of an aquarium.
These teeth not for trituration, they are for
accessing food not rendering it particulate.
Teeth are recurved,
designed to pull one way.
Collection,
storage and
transport of
food
Posterior face honeybee metathoracic leg
showing basitarsal brush, hint of branching
of hairs.
Hairs are branched; pollen transferred from them by
brushes of basitarsus: a tarsal segment enlarged into a
rectangular brush, shaped for this purpose. Cross-body
use of rake and brush draws pollen up into press of leg
of opposite side. Pollen press compresses and
squeezes one-way moving pollen into pollen baskets.
See detailed account in lab outline.
homoplasy
•
•
“Many species of bats are highly specialized
for feeding on nectar and pollen. Their
tongues extend to unusual lengths, often up
to one third the length of their bodies. This
extension is achieved in part by contracting
muscles in the tongue to push blood to the tip,
much as the end of a party toy unrolls when
you blow into it. The tip of the tongue is
covered with conical papillae that increase the
surface area and the bats nectar-lapping
capacity. Furthermore the scales on their
hairs extend from the shafts and act as pollen
traps. The scales on the hairs of bats that do
not feed on flowers usually adhere closely to
the shafts. (Brock Fenton, Just Bats)”.
Tooth reduction has evolved in some of these
herbivorous bats.
Merlin Tuttle
•
“Three scanning electron micrographs of
the hairs of Geoffroy’s Tailless Bat a),
Woermann’s Long-tongued Fruit Bat b),
and a Mexican Bulldog Bat (c) show that
the hairs of different species can be
distinctly different. Note that the scales
on the shafts of the hairs of GTB and
WLF bats protrude more than those of
the animal-eating bat. Protruding scales
in flower-visiting species have been
proposed as pollen traps, permitting the
bats to carry pollen more efficiently. The
similarity of the hairs of the two flower
bats is striking, given that they are from
different families (a) New World Leafnosed bats (b) Old world fruit bats. The
hairs are about a tenth of a millimetre in
diameter.” [Brock Fenton]
homology, homoplasy
•
•
•
Convergent evolution - homoplasy -- describes the acquisition of the same
biological trait in unrelated lineages. The wing is a classic example of convergent
evolution in action. Flying insects, birds, and bats have all evolved the capacity of
flight independently. They have "converged" on this useful trait.
The ancestors of both bats and birds were terrestrial quadrupeds, and each has
independently evolved powered flight via adaptations of their forelimbs. [Wikkipedia]
The branched hairs of bees and the erect scales of bat hairs are another
example of functional homoplasy.
The concept of homology is fundamental to the field of comparative biology. In
1843, Richard Owen defined homology as "the same organ in different animals under
every variety of form and function". Homology is evaluated strictly in an evolutionary
context. That is, organs in two species are homologous only if the same structure
was present in their last common ancestor. Organs as disparate as a bat's wing, a
seal's flipper, a cat's limb and a human arm have a common underlying anatomy
which was present in their last common ancestor and so therefore are homologous
as forelimbs. [Wikkipedia]
Gut diverticulae and storage: sacculate crop of leech: discontinuous
feeder
The leech 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 host. Obviously those
teeth are not homologous with the
teeth of a vertebrate
Diagram from sharon-taxonomy on the web
McGill Office Science & Society
Bird crop
• A crop in a leech and a crop
in a bird: homoplasy?
• ‘acquisition of the same
biological trait in unrelated
lineages’
• Device for discontinuous
feeding arises in birds and
annelids by independent
evolutionary events.
Rocking T Ranch
Mosquito
(Culicidae)
crop; function
of insect
abdominal
tagma
•
•
Another discontinuous feeder, only
finding its blood meal on occasion, the
mosquito must get all its intake in one
event. It uses piercing and sucking
mouthparts elongated into a ‘straw’, halfgrooved appendages adjoined into
channels; like membracids and aphids
feeding on fluid, but on blood not sap.
This insect takes in a large, once-only,
quantity of blood and has to store it for
later digestion. No teeth needed – no
trituration – but where to put the blood
meal?
Diverticulae of the gut tube arise in the
thorax; but the thorax is a locomotory
tagma, its volume mostly occupied by
flight muscle; it must remain a sturdy
fixed-wall ‘box’ – to give proper
anchorage for walking and flying
muscles (the muscle can’t work if both
ends can move). So there is no room
for blood storage in the thorax. On the
other hand the abdomen’s telescoped
segments are designed for expansion.
Some mosquitoes
feed on frog blood.
•
•
The main crop extends into and
occupies the mosquito abdomen. It
receives the blood ingested (a valve
shuts off the midgut) and the abdomen
expands greatly. So one of the
abdomen’s functions as a tagma is
expansion to accomodate food intake.
Since the vertebrate’s blood is under
pressure there is no need for a
mosquito pump (but there is a need to
prevent coagulation – leech and
mosquito solve this ‘chemical’
problem).
Cibarial pump of cicadas,
spittlebugs: fluid feeders
that need to suck
Dilator muscles contract
dropping internal pressure
relative to external: this
pressure differential moves
fluid up stylet bundle.
Where a pump is needed, because the fluid
food is not itself under pressure, a plant
feeding insect evolves a pump: pharyngeal
or cibarial. This is why cicadas, spittle bugs
etc. have such a dilated face.
Sparky’s ice cream, Columbia Mo.
(Puzzle) Aphids don’t need a pump to
feed on sap; cicadas do need a pump to
feed on sap; are there 2 kinds of sap re
pressure? Do cicadas feed on xylem
rather than phloem and xylem has lower
pressure?
Feeding by aphids: piercing and
fluid extraction by Homoptera
•
•
•
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 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; no need to
pump/suck the fluid: note small head and
thorax
transverse
section
stylet
bundle
ghppr
head
Rosy Apple Aphid with stylets inserted in
mpts
frons
plant tissue
colour
coded
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 reached
Aphids can be used to collect
phloem sap. Top photograph:
a feeding aphid with its stylet
embedded in a sieve tube.
scl, sclerenchyma; st, stylet;
x, xylem; p, phloem. Note the
drop of ‘honeydew’ being
excreted from the aphid’s
body. (a) to (e) show stylet
cutting with a microcautery
unit at about 3-5 s intervals
(a to d) followed by a twominute interval (d to e) which
allowed exudate to
accumulate. 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.
Plants in action
Winged aphids can appear in populations and are the basis of dispersal
The aphid has the problem of securing a quiet backwater in its
gut for secretion of enzymes and absorption of the products of
digestion. The pressure of the fluid on which it feeds is a
problem as it pushes the fluid through the gut at a high rate.
And the aphid’s food (sap) is very dilute so it must process
copious amounts. 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 t the two overlain gut walls filter the wanted out of
the unwanted.
Teasel Dipsacus carnivory
Generic name of this plant is derived
from Greek word for ‘thirst’, referring to
perfoliate leaves that collect rainwater.
True carnivory is “typically found in
perennial plants of acid, nutrient-poor
boggy soils” (e.g., bladderwort). Plants
in these nutrient deprived conditions can
benefit from additional Nitrogen and
Phosphorus. But some plant carnivory is
more subtle.
Walter Muma
Dipsacus
Walter Muma
The water accumulated in the leaf bases of
Dipsacus traps small invertebrates (mainly
insects) whose decomposing bodies have now
been shown to provide the plant with nutrients.
Dipteran larvae were added to leaf-base pools
and produced “a 30% increase in seed set”.
First demonstration that this plant can benefit in
this way.
Leaves function to prevent aphids (sap feeders)
from climbing higher to rapidly growing
meristems
water accumulates here