Transcript I Amphibians PPT

Phylum: Chordata
Class: Amphibia
Order Gymnophiona
Order Anura
Order Caudata
Class Amphibia
Derives from Greek:
The Greek prefix amphimeans "both" or "double"
The Greek word bios means
"life.“
Amphibian = “double life”
Class: Amphibia – means
Subclass Labyrithodontia (extinct)
Order Anthracosauria (extinct)
From
Romer
Subclass Lepospondyli (extinct)
Subclass Lissamphibia (living amphibians)
Order Gymnophiona (aka Apoda, Caecilians)
From Linzey 2001
Infraclass Batrachia
Order Anura (frogs and toads)
Order Urodela (Caudata) (salamanders, newts,
sirens, etc.)
From Conant and Collins
Class: Amphibia
Most have 4 limbs, except Caecilians (limbless) and Sirens
(forelimbs only)
Many have webbed feet
Typically the glandular skin is smooth, moist, and lacks
scales
-Caecilians have concealed dermal scales
Lesser Siren
Caecillian
Red-eyed Tree frog
Rough Spotted Newt
Wood frog
Caecilians
Movement onto Land
Life began in the water, animals
are made of mostly water, and all
cellular functions occur in water.
Invasion onto land required
modification of almost every
system in the vertebrate body. The
Amphibian is an example of this
terrestrial transition.
Amphibian Origins
Though actual origins are uncertain, it is clear that there
was plenty of selective pressure for amphibians to emerge
onto land
-the Devonian was a period of tremendous climatic
fluctuation
-Wet and dry spells – dry
spells would have set up
intense competition in
aquatic habitats
-Would favor an ability to
move from one pond to
another
-Oxygen poor waters
would favor air-breathing
Amphibian Origins
-Also, at this time, there was a tremendous radiation of
arthropods into the terrestrial environment
-Centipedes, millipedes, spiders, insects, etc. = food!
-This would create an open niche in a relatively lowcompetition terrestrial environment
Accommodations to be
considered when moving to land
Oxygen content
Oxygen diffuses more readily in air
then water
Development of lungs
Support
Provides little support against gravity
Requires the development of strong
skeleton and limbs to get around
Accommodations to be considered
when moving to land
Development of limbs
required only a few minor
modifications
-elongation of proximal
elements into long-bones
of limbs
-Proliferation of more
distal elements into
bones of feet
-Elaboration of pectoral
and pelvic girdles (for
anchoring the limbs)
Accommodations to be
considered when moving to land
Temperature regulation
Air fluctuates in temperature more then
water
Requires behavioral and physiological strategies
to protect themselves from thermal extremes
Homeothermy—regulated constant body
temperature
birds and mammals
Habitat diversity
Diverse biomes to live in and adjust to
Characteristics of
Class: Amphibia—on both sides
4,200 species
Require a metamorphosis from
water to land during development
Skin is thin and requires moisture
Ectothermic—body temperature
varies with outside changing
temperature (cold blooded)
Body Plan
Bilateral symmetry
Skeleton mostly bony
Small teeth
Segmentation-head normally
distinct from body
Four limbs (except caecilians)
Webbed feet
no nails or claws, 4-5 digits
Skin
Made of Keratin, a tough protein that
protects against abrasions and water
loss
Moist
Two layers—epidermis and dermis
With many glands
Serous glands secrete poison; effectiveness
varies from species to species
Mucous glands waterproof the skin
Pigment cells—Chromatophores
Respiration
Air is forced into the lungs with mouth
muscles [positive pressure]
Air can be diffused through skin and the
inside of the mouth
The majority of carbon dioxide is
released through the skin
Sound is created by forcing air over
vocal cords and a large pair of sacs in
the floor of the mouth
Respiration
-Gas exchange occurs through
lungs, gills, and/or the skin
-Some salamanders have no
lungs (secondarily lost)
Eastern Red-backed
Salamander – no lungs
Larval tiger salamander showing
gills
Adult mudpuppy showing
gills
Circulation
Closed system
Origin of the Systemic and
Pulmonary Circuits
3 chambered heart
2 atria
1 ventricle
Spiral valve helps separate the flows
of oxygenated vs unoxygenated blood
Nutrition
Carnivores feeding on
insects, spiders, worms
slugs, snails, millipedes
Protrusive tongue is
attached at the front of the
mouth
Digestion
Complete digestion with both
intracellular and extra-cellular
digestion
Excretion
Pair of mesonephric kidneys
Urea main nitrogenous
waste
Nervous System
Ten pair of cranial nerves
Senses
Smell—olfactory
epithelium
Hearing--ear
Hearing
One advance associated with a more terrestrial existence is
the refinement of the ear
-the amphibian ear, unlike that of fishes, consists of
three components
-Inner ear, middle ear, outer ear
-There is increased sensitivity to accommodate
airborne sounds
Reproduction
Sexual with both “internal” and external
fertilization
In the spring, males vocally attract females to
mate with
Eggs are laid in large masses and can be
anchored to vegetation, simply float in water,
or laid under logs in moist ground
Packet of sperm may be left on vegetation and then
inserted by the female herself
Male may force eggs to be evacuated from the
female as he discharges his sperm over the eggs —
amplexus
Reproduction
Amphibian eggs are very vulnerable to desiccation.
Hence, amphibians are reproductively constrained to exist
in moist environments.
Frog eggs
Toad eggs
Salamander eggs
Spermatophores
Development
Eggs hatch into aquatic
larva having external gills
and tail
Metamorphosis
Reproduction
Australian Marsupial frog (A)
(use pouch on dorsum)
Surinam Frog Surinam (B)
(babies in skin on dorsum)
Poison Dart frog (C)
(carries tadpoles from forest floor to
canopy)
Darwin’s frog (D)
(babies mature in vocal pouch)
Gastric Brooding frog
(keeps young in stomach!)
Environmental Interaction
Require a somewhat cool
environment
Most amphibians hibernate during
winter months in soft mud of the
bottoms of pools and streams
Some can tolerate freezing
temperatures by making a type of
antifreeze by accumulating glucose
and glycerol in body fluids
Environmental Interaction
Are both predators and prey to
others, for protection amphibians
have developed
Poison glands
Urinate on predator
Strong legs for leaping away
Biting at predators
Inflate lungs to avoid being
swallowed
Camouflage
Importance of
Amphibians
To Ecosystem – Pest control, food
for other animals
To humans – Food, genetic
research
They are “nature’s indicator”
Yikes
Worldwide, populations of frogs
have been decreasing and
experiencing mutations. No one
knows the cause for sure!!!!
Pollution, acid rain, ozone depletion,
pesticides/chemicals, introduction of
non-native predators are just a few
ideas
Order Gymnophiona caecilians (aka Apoda)
Limbless (“naked snake”)
160 species
Tropical forests of South America,
Africa, and South East Asia
Most species totally blind
Burrow or aquatic
Carnivores
Order Caudata
salamanders, newts, sirens
“having a tail”
360 species
Found in all North America, tropical
areas of Central and northern south
America
Carnivorous both as larva and adult
Range from about 2” in length (Patchnosed Salamander) to over 5’ in length
(Japanese Giant Salamander)
Order Anura
frogs and toads
“without tail”
3,400 species
Carnivores and herbivores
Found in temperate and
tropical regions throughout the
world except New Zealand