Transcript Amphibians

Bio II
Rupp
Background
Evolved 370 mya from sarcopterygii
 Name means “double” “life”

Adaptation to Land

Bad hypothesis
 Movement overland from shrinking pools of
water to larger pools
 Short overland crossing do not allow time for
change
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Better hypothesis
 Escape from predation and competition to
land where resources were plentiful—insects
and plants
Characteristics of Early Amphibians

Similar to
sarcopterygii
 Skull
 Limbs
 Shape
Icthyostega continued
Four strong limbs—homologous to
pectoral fins
 Lung breather
 Teeth for eating fish
 Seven toes on hind foot—today’s
amphibians have five

Diversification
Evolutionary split in
the Devonian and
Carboniferous
period
 One line became
modern amphibians

Diversification continued
Other line was forerunner to modern
reptiles
 Approximately 4500 species of
amphibian today

 Anura—3000 species
 Urodela—400 species
 Apoda—160 species
Modern Characteristics
Aquatic Larva to Terrestrial Adult-Metamorphosis
Moist, thin, scaleless skin
Claw-free feet, typically webbed
Gills, lungs, and skin for
respiration
No multicellular egg membranes
Large mouth with upper and
lower teeth
Three-chambered heart
Ectothermal
Paired kidneys
Ten pairs of cranial nerves
Separate Sexes
Order Anura
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Name means “without
tail”
Frogs and toads
Found worldwide
except polar regions
Toads = rough and
bumpy skin
Frogs = smooth and
moist skin
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Spend at least part of
their life in water,
some are totally
aquatic
Built to jump
 Long, strong hind legs
 Short, shock absorbing
forelimbs
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Eat almost anything
Return to water for
fertilization and
mating
Larval tadpole stage
Toad versus Frog
Order Urodela
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Tailed amphibians
Elongate body, long
tail, moist skin, four
limbs
Few centimeters to
1.5 meters long
Carnivorous
Typically nocturnal
Found in the
Americas, Africa, Asia,
and Europe
Many lay eggs in
water—
metamorphosis
Family Plethodontidae
is the largest group—
lungless, gas
exchange through
skin
 Terrestrials hatch into
mini adults—direct
development
 Internal fertilization—
spermatophore
 Some females retain
eggs until hatching
 Necturus

Urodelans
Urodelans
Urodelans continued
Paedomorphosis—retention of pre-adult
structures
 Non-metamorphic species are termed
perennibranchiate
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Apodans
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Name means “without
feet”
Typically called
caecilians
Resemble snakes
Average 30cm in
length some reach
1.5m
Small eyes located
under skin or bone—
typically blind
Burrowers
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Relatively little is
known
Teeth for prey capture
Chemosensory
tentacles on head
Believed to have
internal fertilization
Some females stay
with eggs until
hatching
Some are viviparous
Found in Asia, Africa,
and S. American
tropical regions
Apodans continued
External Covering

Two major functions
 Respiration
 Protection

Gas exchange is
aided by mucous
glands to keep the
skin moist
External covering continued
May secrete poisons
 May desiccate
quickly if not near
water
 Nocturnal to avoid
desiccation

Internal Anatomy
Strong vertebral
column to support
weight on land
 Strong limbs
 Pectoral and pelvic
girdles
 Cervical vertebrae
for neck movement
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Internal Anatomy—circulatory
system
Double circulation—two loops
 Pulmonary circulation—carries
deoxygenated blood from heart to lungs
 Systemic circulation—carries
oxygenated blood to body
 Faster blood flow than a single loop
system like fish
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Internal Anatomy—circulatory system
continued
Internal Anatomy—circulatory system
continued
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First division in pulmonary
and systemic pumping
Deoxygenated blood enters
sinus venosus of right atria
Oxygenated blood enters left
atria
Blood enters the ventricle—
structure minimizes mixing of
bloods
Conus arteriosus valve
separates blood and sends
to lungs or body
Respiration
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Larval amphibians
use skin and gills
Adults use skin and
lungs
Cutaneous
respiration is
important due to
small surface area
of lungs

Positive pressure
breathing
 The mouth changes
the pressure in the
airway
 Nostrils control
direction of the airflow
Respiration continued
Digestive system
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Adults are
carnivorous
Larvae are typically
herbivorous
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Organs
 Pharynx
 Esophagus
 Stomach
 Liver
 Gall bladder
 Small intestine
 Large intestine
 Cloaca
Digestive system continued
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Elastic stomach and
esophagus allow
swallowing of large
prey
Stomach secretes
gastric juices
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Pyloric sphincter
allows digested food
to move to the small
intestine
Upper portion of
small intestine is the
duodenum
Middle portion of the
small intestine is the
ileum
Digestive system continued
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Mesentery holds the
small intestine
together
Digested food,
urinary wastes, and
eggs and sperm
pass into the cloaca
before exiting the
vent
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Liver produces bile
stored in the gall
bladder
Pancreas secretes
enzymes to help
break down food in
the small intestine
Excretory system
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Kidneys are the
primary organ
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 One located on each
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side of the spine
 Filter nitrogenous
wastes, mix with water,
and excrete as urine
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Kidneys to urinary
ducts to urinary
bladder
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Bladder can serve as
a water reservoir
organ in dry times
Larval amphibians
excrete ammonia
which is toxic
Adults transform
ammonia into urea,
which is less toxic and
conserves water
Excretory system continued
Nervous system
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Brain is divided into lobes
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Olfactory
Cerebrum—behavior and learning
Optic lobes
Cerebellum—muscular coordination, not well
developed
 Medulla oblongata—involuntary muscle control,
heart and breathing
Ten pairs of cranial nerves
 Spinal cord and PNS
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Sense organs
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Larval amphibians
have a lateral line
system like a fish—it
is lost during
metamorphosis
Sense organs continued
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Eyes
 Covered by nictitating
membrane
 Large optic lobes
Sense organs continued
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Hearing
 Tympanic membrane—external eardrum
 Columella—small bone between typanum and
internal ear
 Inner ear fluid carries vibrations from columella
 Sounds are converted to electrical impulses by
small hair cells
 Electrical impulses are transmitted to the brain
Reproduction—life cycle
Males have bean-shaped testes near the
kidneys
 During breeding the sperm cells pass to
kidneys, then urinary ducts, then the cloaca
 Females have thin-walled ovaries located
near the kidneys
 Eggs mature, burst through the ovaries,
move towards oviducts, become coated in
jelly-like material, and exit the cloaca
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Reproduction—courtship and
fertilization
Mating calls are species unique—caused
by forcing air back and forth from lungs to
mouth over vocal sacs
 Amplexus—males climb onto female and
embrace her
 When the female releases the eggs the
male coats them in sperm—direct external
fertilization
 Frog calls
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Reproduction-courtship and
fertilization
Reproduction--metamorphosis
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A few days after
fertilization tadpoles
hatch
Tadpoles survive
using an attached yolk
sac
Develop three pairs of
gills
 Development of
operculum
 Spiracle on left side
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Mouth eventually
opens, legs grow, and
tail and gills disappear
Thyroxine is the
hormone responsible
for causing the
physical changes
Reproduction—metamorphosis
continued
Reproduction—metamorphosis
continued
Some species do not lay eggs in water, but
they find a moist place or construct small
nests
 Some salamanders remain in a larval stage
their entire lives (Mexican axolotl—
paedomorphosis) (Necturus—
perrenibranchiate)
 Some amphibians bypass metamorphosis
and hatch as miniature adults
(metamorphosis in egg) (Longtail
salamander)
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Reproduction—metamorphosis
continued
Reproduction—parental care
Some species offer
protection to their young
 Many times the father is
the protector
 Male Darwin frog,
Rhinoderma darwinii,
takes young into his
vocal sacs—they hatch
and go through
metamorphosis in his
body (found in Chile)
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Reproduction—parental care
continued
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Female gastric-brooding
frogs (probably extinct)
 Swallow the eggs
 Development in stomach
 Stomach stops producing
acids during brooding
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Some females sit on
their eggs, typically
poison dart frogs
Reproduction—other parental
care strategies
Reproduction—other parental
care strategies