Amphibia

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Amphibia
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Amphibians

• 370 mya amphibians evolved from lobe-finned fish
• first terrestrial vertebrates
• Left water escaping predation, food competition
  for more space
• Only invertebrates (insects) on land - abundant
  food source

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Icthyostega and Acanthostega

• Early amphibians
• Icthyostega large tail fin with lateral line
  canals on head
• Large teeth diet of fish
• 7 toes on each foot (5 toes present amphibians)
• Acanthostega8 toes on each foot

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Ichthyostega Acanthostega
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Shared Characteristics with Lobe-Finned Fish

• Similar skull and Vertebral column
• Amphibian limb bones similar to fins
• Lobe-finned fish pelvic pectoral girdles
  homologous to amphibian hind forelimbs
• Early amphibians had lungs
• Sense organs detect smell sound

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Diversification of Amphibians

• Amphibians split into 2 lineages in Devonian
  Carboniferous periods
• Split into amphibians reptiles
• 4500 amphibian species-3 orders
• Anura 3900 species of toads frogs
• Urodela 400 species of salamanders
• Apoda 160 species of caecilians legless tropical
  amphibians

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Golden Toads Costa Rica
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Modern Amphibian Characteristics

• Change from larval stage to adult terrestrial
  form by metamorphosis
• Thin, moist skin without scales
• Feet often webbed, no claws
• Use gills, lungs or skin in respiration
• Eggs without membranes (shells) laid in moist
  places with external fertilization

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Anura

• Frogs and toads
• Found in dessert to tundra to tropical forests
  everywhere except for polar climates and a few
  isolated islands
• Toad rough, bumpy skin
• Frogs smooth, moist skin

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• Most live part of life in water
• Some permanently in water others live reproduce
  on land
• Long, muscular legs, compact body, strong
  forelimbs
• Anuran tailless
• Carnivores eat any animal they capture
• Larva called tadpoles

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Frog Eggs
Toad Eggs
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Frog vs Toad Tadpoles

• Frog tadpoles are usually brown and large
• Toad tadpoles are black, smaller and
  metamorphosize much quicker

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Salamander Larva

• Salamanders are called larva when they are newly
  hatched
• Eggs are laid in a mass

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Tadpole Development
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Young Adult
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Urodela

• Salamanders long tails moist skin
• Range from fully aquatic to fully terrestrial
  live in moist places (under logs/rocks)
• Carnivores that are active at night
• Most live in N Central America
• No species found in Australia

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• Absorb O2 release CO2 through skin
• Most lay eggs in water swimming larva
• Land eggs hatch into miniature adults

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Spotted Salamander
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Axolotl-Ambystoma mexicanum
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Apoda

• Caecilian legless amphibians
• Small eyes located beneath skin/bone
• Rarely seen most burrow in soil some are
  aquatic
• Teeth used to eat worms/invertebrates
• Some lay eggs, some live birth
• Chemosensory tentacle on the side of their head
  to locate prey

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Amphibian Characteristics

• Amphibians met the challenges of living on land
  in a variety of ways
• External Covering (Skin) - 2 purposes
  respiration protection
• Skin is moist permeable to H2O gases rapid
  diffusion of H2O CO2

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Mucous Glands

• Lubricant keeps skin moist in air makes frog
  feel slimy
• Skin also secretes foul-tasting or poisonous
  substances
• Amphibians live in wet or moist areas to prevent
  dehydration
• Dessert dwellers live deep in burrows only come
  out in rain

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Warts from Toads?

• That is a misconception, they do release an
  irritant that can cause discomfort if it gets
  into mucus membranes such as your mouth or eyes
• Washing your hands after handling a toad is
  advised

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Internal Anatomy

• Strong skeleton supports body against gravity
  (not H2O)
• Vertebrae interlock to form a rigid structure
• Pectoral pelvic girdles transfer bodys weight
  to limbs

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• In frogs the tibia fibula are fused into a
  tibiofibula the ulna radius are fused into
  the radio-ulna to absorb the forces created by
  jumping
• Frogs have few vertebrae
• Cervical vertebra allow neck movement
• Posterior end fused into a single bone called the
  urostyle

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Vertebrate Limb Regeneration

• Since 1768 it has been known that some organisms
  can regenerate lost limbs.
• Recently scientists discovered that a group of
  cells on newts are able to dedifferentiate, grow,
  and then re-differentiate into several cell types
  to produce a new limb
• Researchers hope to use this information and
  apply it to human medicine

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Heart and Circulatory System

• 2 separate loops
• Pulmonary circulation carries deoxygenated
  blood from heart to lungs returns oxygenated
  blood to heart
• Systemic circulation carries oxygenated blood
  from heart to muscles organs and brings
  deoxygenated blood back to the heart

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Heart and Circulatory System

• Faster blood flow to the body (compared to single
  loop system in fish)
• All terrestrial vertebrates have double loop
  circulatory systems
• Amphibians have 3 chambered heart

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Blood flow through heart sinus venosus ?right
atrium ?oxygenated blood from lungs enters left
atrium ?both atrium flow into single ventricle
but do not mix ?conus arteriosus deoxygenated
blood to lungs oxygenated blood to body
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• An amphibian heart does not mix oxygenated and
  deoxygenated blood very much
• Mixing of the two types would be a disadvantage.
  Why?
• Because mixing blood would lower the amount of
  oxygen dissolved in the blood, thus lowering the
  amount of oxygen delivered to the amphibians
  tissues

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Respiration

• Larval amphibians respire through gills and skin
• Most adult amphibians respire through lungs
  (pulmonary respiration) and skin
• Pulmonary respiration unique positive-pressure
  breathing changing volume and pressure of air
  in mouth 2 step process

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Cutaneous Respiration

• Small lung surface area so respiration also
  occurs through skin

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Cell Respiration

• The energy demands of land vertebrates require
  that their cells receive a continuous supply of
  oxygen to function as the terminal electron
  acceptor for cellular respiration
• The double-loop circulatory system provides an
  efficient way to deliver oxygen to tissues

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Digestive System

• Adult amphibians are carnivores
• Small amphibians consume insects and other
  arthropods large sometimes consume mice, snakes,
  fish other amphibians
• Many amphibian larva are herbivores feed on algae
  or bacteria

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• Digestive system includes pharynx, esophagus,
  stomach, liver, gallbladder, small large
  intestine cloaca
• Glands in stomach secrete gastric juices to
  digest food
• Pyloric sphincter relaxes and allows food to
  enter small intestine

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• Small intestine digestion is completed here
  nutrients pass through capillary walls into
  bloodstream
• Duodenum upper small intestine
• Ileum middle small intestine
• Mesentery membrane that holds small intestine
  in place

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• Lower small intestine leads to large intestine
• Indigestible waste collects and is pushed out by
  muscle action into cloaca
• Waste from kidneys urinary bladder either
  eggs or sperm also pass into cloaca.
• Material exits body through vent

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Other Digestive Organs

• Liver produces bile that is stored in gallbladder
• Bile breaks down fat for digestion
• Pancreas secretes enzymes that break down food in
  small intestine

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Digestive Differences

• Food from plants takes longer to digest than food
  made from animals because plants contain
  indigestible cellulose.
• Consider the differences in food eaten by
  tadpoles and adult frogs. Would you expect to see
  the same digestive systems in both?
• No a tadpole eats plant matter and its small
  intestine is longer and more coiled allowing for
  more time to digest the algae and plants

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Excretory System

• Kidneys primary excretory organ
• Filter nitrogenous waste from blood are flushed
  from body as urine
• Urine flows through urinary ducts from kidneys to
  cloaca
• From cloaca urine flows to urinary bladder
• During dry periods, water can be reabsorbed from
  the urine in the bladder

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• Most amphibian larva excrete nitrogen containing
  wastes as ammonia
• Ammonia is very toxic and must be removed from
  the body or diluted with H2O
• Adult amphibians convert ammonia into urea

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Nervous System

• Consists of brain, olfactory lobes (center of
  sense of smell), cerebrum (behavior and
  learning), optic lobes (process info from eyes),
  cerebellum (muscular coordination), and medulla
  oblongata (controls organ functions)

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• Spinal cord conducts signals from all parts of
  the body to the brain back
• Spinal nerves branch from the spinal cord to
  various parts of the body

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Sense Organs

• Larval amphibians have lateral line system,
  adults do not
• Well developed sense of smell, sight and hearing
• Eyes covered by transparent membrane called a
  nictiating membrane

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• Sound receptors in inner ear
• Sounds transmitted by tympanic membrane (eardrum)
  the columella (small bone extending between
  tympanic membrane and inner ear)
• Sound vibrations are converted to nervous
  impulses by sensitive hair cells then transmitted
  to brain through a nerve.

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• The lateral line of a fish functions similarly to
  the tympanic membrane of an amphibian both
  detect vibrations of water or air in their
  environment

Tympaniuim
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Amphibian Reproduction

• Reproduction methods are one of the biggest
  differences between aquatic and terrestrial life
  forms
• Most amphibians need water to reproduce
• Eggs are laid in the water
• Most of their early life is in water

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Lifecycle

• When frogs emerge from hibernation, they move in
  large numbers to ponds and slow moving streams
• Males call by moving air from the mouth to the
  lungs, vibrating vocal folds to attract females
• When a female chooses the male, they engage in a
  in an embrace with the male on the females back
  called amplexus
• The embrace can last for hours or days until the
  female releases her eggs and the male fertilizes
  them

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Internal Reproductive Events

• In the female, eggs enlarge, mature, burst
  through the thin ovarian walls into the body
  cavity during breeding season
• In the male, sperm develop in the testes and move
  through tubules to the kidneys and urinary ducts
  leaving the body through the cloacal opening
• Reproduction occurs in the water in most
  amphibian species

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Metamorphosis

• Tadpoles emerge from eggs in a few days
  metamorphosis begins
• The tadpole gets nutrition from yolk stored in
  its body
• Controlled by increasing levels of the hormone
  thyroxine
• First three pairs of gills develop
• Later its mouth opens so it can feed
• Growth occurs
• Legs grow and tail and gills disappear
• Mouth gets wider, teeth and jaws develop and
  lungs begin to function

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Parental Care

• Common among amphibians
• Increases odds of survival of offspring
• Some keep offspring in their mouth or swallow
  them as they develop
• Some sit on the eggs to keep them from drying out