Feeding

for quiz 4

Diversity in Feeding Modes

-diversity in feeding modes reflects diversity in habitat and locomotor patterns

-most species are carnivorous (including eating anthropods)

-venom evolved independently in snakes and lizards

-some are herbivores

Suction Feeding

• In water, food is often supported above the
substrate, so food can be manipulated in water
without requiring effort to support it.
• Swallowing does not require saliva for lubrication.
• But, a predator can move and create pressure
waves that push prey away, so suction is useful.
• Suction feeding generally employed by aquatic
salamanders (including larvae), aquatic frogs,
tadpoles, some turtles.
• Requires generating negative pressure within the
buccal (oral) cavity, typically by expanding its
volume.

Terrestrial Feeding Mechanisms

-Akinetic, nonprojectile feeding

→simplest feeding simplest, not necessarily ancestral

→a rigid skull and a hinged lower jaw

-projectile feeding mechanisms

→independently evolved

→projection of tongue 

Cranial Kinesis

• Widespread among vertebrates; absence is often a secondary loss.

• Tegu and monitor lizards use inertial feeding; food is held aloft in the jaws, the head is drawn back, and then the prey is momentarily
released while the head is rapidly thrust forward and the grip
reestablished.

• Most snakes use unilateral feeding, in which the right and left bones of
both the upper and lower jaws move alternately.
→ This allows snakes to swallow prey items too large to be transported by the
tongue or by inertial feeding.

Envenomation

• Venom delivery is fundamentally a strategy for
prey capture; its use in defense is only a
secondary function

• Venomous lizards: the Gila monster
(Heloderma suspectum), the beaded lizard
(H. horridum), and monitor lizards (genus
Varanus) such as the Komodo dragon.

• All other venomous reptiles are snakes.

• Different venoms have different effects.
→One snake’s venom is a complex blend of
ingredients with diverse effects.

Pit Organs

• Pit vipers have a pair of sensory structures known
as pit organs on the side of the head, between the
nostril and the eye, and analogous pit organs,
forming a series of paired structures along the lips,
are present in many boas and pythons.
• Pit organs are sensitive infrared receptors and
convey spatial information about the thermal
environment.
• The image is superimposed on the visual image, so
snakes see light and heat together.
• Pit organs are used to localize endothermic prey
under dark conditions

Herbivory

• Plant material has a lower energy content than
animal tissue.
• Vertebrates can’t digest the cell wall.
• Herbivory involves modification of the teeth
and gut.

→occurs in few species of amphibians and reptiles

Omnivory and Frugivory

• Some turtles and a substantial number of
lizards are omnivorous, consuming a
considerable amount of vegetation in
addition to animal prey.
• Fruit-eating animals (frugivores) have few
problems processing food
because fruits are
characterized by
large, energy-rich cells
that are easily ruptured.

Herbivory Challenges

• Leaf-eaters (folivores) must release nutrients from
within the cells of leaves.
→ Many vertebrates have acquired symbiotic intestinal
microorganisms that produce enzymes capable of breaking
down cellulose into simpler compounds that can be
absorbed by the host.

→Each generation of animals must obtain an inoculum of
endosymbionts by ingesting feces of other individuals
(coprophagy) or by eating soil contaminated by feces.

• Herbivorous lizards bite off pieces of plants but don’t
chew them.
→They have a large colon where fermentative cellulose
digestion takes place.