Lecture 3

Mucus: is a viscoelastic sol-gel common in animals.
Mucus is a ‘solution’ of glycoproteins, a viscous colloid also containing chemicals like
antiseptic enzymes – lysozymes -- that act against microbes. It can function as a barrier
against bacteria and viruses and as a filter.
There are many filter-feeding animals eating particulate food that they must
concentrate from their environment (e.g., amphioxus); mucus is commonly used in this
filter process: e.g., produced by cells in the bottom of the pharynx of amphioxus, it is
driven up the pharynx walls to trap small protozoa (e.g., diatoms) out of a water stream.
Within Phylum Mollusca is the Class Gastropoda, ~35000 species.
Pulmonates are a subclass of gastropoda and include land snails; the name
refers to their conversion of the mantle cavity into a lung.
This gastropod
moves on its
single foot using
waves moving
along [the
foot’s] ventral
“the force of these waves
is coupled to the substratum by
a thin layer of pedal mucus”
Denny 1980
There are monotactic and ditactic gastropod species: meaning that in some gastropods the
foot is divided into two parallel feet; these ditactic snails still move with pedal waves.
A spectacular feature of the damp forests of northwestern coastal NA.
Pacific Banana Slug
pneumostome: entry to lung
See video of pedal waves http://www.flickr.com/photos/turtblu/3424848753
Mucus is critical in the pedal locomotion of Pulmonates
Mantle cavity of pulmonates has been converted into a lung:
hence ‘pulmonate snails’. of which slugs are just one sort. The
edges of mantle cavity seal to the back except for the
pneumostome opening; roof of mantle cavity vascularized as a
lung for gas exchange.
From Wikimedia Commons
Arion ater, black slug
Denny’s abstract: use the abstract as entry to the paper and read just the parts of the
paper that the abstract points to.
“Gastropods move using a single appendage – the foot. For many gastropods the
power for locomotion is provided by muscular waves moving along the ventral surface
of the foot, the force of these waves being coupled to the substratum by a thin layer
of pedal mucus. This mucus acts as a glue, allowing the animal to adhere to the
substratum on which it crawls. This adhesive ability is advantageous, particularly to
animals (such as limpets and certain snails) which live in intertidal or arboreal habitats
where the forces of waves and gravity must be resisted while the animal forages.
However, the adhesiveness of the pedal mucus presents the animal with a problem.
How can an animal with only one foot walk on glue? [Some snails do have nominally 2
‘feet’.] This question was studied using as an example the terrestrial pulmonate slug,
Ariolimax columbianus, and locomotion is found to depend on the unusual mechanical
properties of the pedal mucus.”
If one is to crawl across a solid surface using body waves you need to obtain purchase.
This means gripping the substratum at some location, fixing that spot, so that one gains
ground with the wave. If there is no purchase the waves will simply oscillate in situ and
there will be no forward progress.
from Wikkipedia
Wikkipedia Ariolimax columbianus
“The yield-heal characteristics of this mucus are ideally suited to the
locomotion of A. columbianus. [YIELD: sol; HEAL: gel/glue] During
locomotion 12 to 17 muscular waves are present on the slug’s foot;
each wave being an area of forward motion, initiated at the posterior
end of the animal as the tail is pulled forward. A wave is translated
anteriorly until it reaches the head of the animal where it is dissipated
as the head moves forward. ...The waves alternate with interwaves,
these being stationary relative to the ground. The mucus beneath the
leading edge of the interwave quickly heals, and most of the interwave
rests on mucus in its solid [gluing] form.”
...the yield-heal cycle of the pedal mucus allows it to act as a
material ratchet, facilitating forward movement but resisting
backward movement. The result is effective adhesive
Many plants are wind pollinated, but many animals, especially
insects, serve as pollinators of flowering plants.
• Pollen is the way haploid male genetic material moves between
flowers of the same species: from the anther of one flower to the
stigma of another: this is called cross-pollination.
• The most abundant of animals are beetles, so perhaps it is not
surprising that beetles are the largest taxon of cross-pollination
• But cross-pollination of flowering plants is also carried out by birds,
bees, flies, butterflies, moths and bats.
Vector: there are many ‘vectors’, e.g.,
force vectors, but in this case it means
‘the biotic agent that moves pollen from
the male anthers of a flower to the
female stigma of a flower to accomplish
fertilization’ (Wikki).
Bee with pollen baskets loaded.
[Posterior] inner face of honeybee hind
leg showing basitarsal brush, auricle &
rake of pollen press. (Rake teeth are
just visible beyond the auricle on the
leg’s outer [anterior] surface).
Pollen is groomed from branched setae (hairs) of
head, thorax and abdomen with other setae
(differently shaped), formed as a brush on the
enlarged basal tarsal segment. Cross-body use
of an opposing leg rakes the pollen from the
brush of each hind leg, drawing it up into a
specialized segment joint called a pollen press:
flexing compacts and squeezes pollen up into the
pollen baskets (corbiculae) on the hind leg’s
external surface.
Buzz pollination: deliberate mechanical dislodgement of pollen , see recent
literature, e.g., Paul DeLuca.
Pollen carried on the body in branched hairs and later groomed by leg brushes and
compacted into the baskets = corbiculae (outer surface of hind tibia).
“From the head and fore parts of the body the pollen grains are cleaned off by the
pollen brushes of the front legs, and from the latter they are scraped off upon the
broad inner surfaces of the basitarsi of the middle legs. [Monocondylic joints are
useful in conferring necessary range of leg grooming movements.] These legs are
then grasped one at a time between the brushes of the basitarsi of the hind legs
and drawn forward, thus transferring the pollen to the inner (posterior) surfaces of
the hind basitarsi. “
POLLEN PRESS : “...the bee brings her hind legs together and moves them
alternately up and down. Bu this action the [rake] of the descending legs scrapes a
small mass of pollen from the basitarsal brush of the other leg. The pollen
detached by the [rake] falls on the surface of the auricle and adheres to it. Then
by an upward flexion of the basitarsus on the tibia, the pollen on the auricle, hld in
place by the [rake] is pressed up into the lower end of the tibial basket.”
A bee’s body surface (the exoskeleton) is the basis for several external structural
adaptations for pollen transport. By contrast, nectar access and transport involves
the mouthparts (labium and maxillae, not the mandibles) and a storage chamber
within the gut, the crop. Much of the gathered pollen becomes bee food along
with the nectar rewards.
“Propolis is the resinous gum that bees obtain mostly from th buds of trees and
use for stopping cracks or crevices in the hive, and also for strengthening the wax
in comb building. Both pollen and propolis are carried to the hive in the baskets of
the hind tibiae.” (Snodgrass, p. 108)
“a glue or resin-like product elaborated by bees to serve a cement in cases where
wax is not sufficiently tenacious” (Torre-Bueno)
Snodgrass, R.E. 1956. Anatomy of the
Honey Bee. Comstock, Ithaca, N.Y.
Some bat (Chiroptera) species are pollen
vectors: they specialize in feeding on nectar
and pollen. Compared to insectivorous bats
they have reduced dentition and unusually
long tongues, often up to 1/3 the length of
their body; they hover in flight and lap nectar
from flowers.
M. Brock Fenton. Just Bats. Univ. of Toronto Press
“Three scanning electron
micrographs of the hairs of bats:
Geoffroy’s Tailless Bat (GTB) a),
Woermann’s Long-tongued Fruit Bat
(WLF) b) and a Mexican Bulldog Bat
(c). “Note that the scales on the
shafts of the hairs of the GTB and
WLF bats protrude more than those
of the insect-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
Leaf-nosed bats (b) Old world fruit
bats. The hairs are about a tenth of
a millimetre in diameter.” [Brock
Convergent evolution - describes similar forms that evolve in different
lineages through similar selection pressures. A common ancestor of bats and
birds was the first terrestrial quadruped, but then each lineage independently
evolved powered flight via adaptations to their homologous forelimbs. They
"converged" on a useful trait, forelimb flight: the cladistic term for this is
homoplasy: it means ‘similarity of form’.
The branched hairs of bees and the erect scales of bat hairs are another
example of similarity of form produced in different lineages by similar
selection pressures; again, this similarity is not due to homology but by
analogous function arrived at independently.
light shows the branched hairs of bees
bat hais SEM
Sensory capacities of animals differ: different sensory modalities are
developed: sight, sound, smell: light, mechanical waves, chemicals.
Katydids and dogs hear ultrasonic sound
frequencies . Dogs access a world of smells we
cannot. The vision of a hawk circling high is of
such superior resolution (fovea: special highdensity of visual receptors) it can see and stoop
on mice running on the ground far below.
A flowering plant, being under selection to
reproduce, must set signals appropriate to the
sensory biases of its pollen-carrying vectors.
Appropriate signals will be different for nocturnal
beetles than hummingbirds. Hummingbirds are
particularly sensitive to red and plant species
pollinated by hummingbirds set red flowers.
In like manner flowers pollinated by bats
may use something appropriate to the bat’s
acoustic specializations: to its echolocation
by ultrasonic sounds.
A leaf specialized to
attract bat pollinators
Simon R., Holderied M.W., Koch
C.U., von Helversen O. 2011.
Floral acoustics: conspicuous
echoes of a dish-shaped leaf
attract bat pollinators. Science
333: 631-633.
A bat-pollinated rainforest vine
Marcgravia, has evolved a dishshaped leaf (sometimes 2) with
the upper concave side facing
oncoming bat pollinators. This
‘dish’ reflects back the echoes
made by the bat as a ‘echo
signature’, localizing the flower
within the sensory surround of
the bat.
Flower shape may be adapted to only
allow access by hummingbirds, e.g.,
long-deep corolla requiring a long thin
beak to access nectar. Selection
discriminates between the effective
pollinator and other species that are
less so.
Unlike bees, hummingbirds
don’t collect pollen; they go
for the nectar with specially
modified tongues and beaks;
but they do pick up pollen and
transfer it. From the plant’s
point of view its a good thing
the bird doesn’t groom as
much as bees.
Anderson B., Cole W.W., Barrett S.C.H. 2005. Specialized bird
perch aids cross-pollination. Nature 435: 41-42.
In South Africa a plant,
Babiana, is called ‘rat’s tail’
because it grows a “curious
sterile infloresence axis”.
The function of this plant
part is to provide a perch
for visiting , and pollinating,
sunbirds. The paper by
Anderson et al. describes
experiments demonstrating
perch removal reduces the
plant’s fertility.
Many animals (beetles, ants, hawkmoths) feed on
the pollen and nectar rewards of plants. It is a
widespread and critical relationship.

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