AMPHIBIAN NOTES

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AMPHIBIANNOTES
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EXTERNAL STRUCTURE AND MOVEMENT

• Amphibian skin does not have scales, feathers, or
  hair.
• It does have secretions that help with
  protection.
• These glands also keep skin moist to prevent
  drying.
• They also produce toxic chemicals that discourage
  potential predators.

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EXTERNAL STRUCTURE AND MOVEMENT

• Chromatophores are specialized cells in the skin
  that are responsible for skin color and color
  changes.
• Cryptic coloration, aposematic(warning)
  coloration, and mimicry are all common in
  amphibians.

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Support and Movement

• Animals that live in water are partially
  supported by water.
• Animals that live on land have to support
  themselves against gravity.
• Amphibian skulls are flattened, are relatively
  small, and have fewer bones than water-dwelling
  animals.
• These changes keep the skull light so it can be
  supported out of water.
• Amphibians also have changes in jaw structure and
  muscles to allow them to crush prey held in the
  mouth.

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Support and Movement

• The amphibian vertebral column is modified to
  provide support and flexibility on land.
• Amphibians do have a neck.
• They also have a sternum which supports the
  forelimbs and protects internal organs.
• Amphibians have a pelvic girdle that has 3 bones.
  
• These bones attach pelvic appendages to the
  vertebral column.
• This is very important in providing support on
  land.

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Support and Movement

• Amphibians depend more on appendages than on the
  body wall for movement.
• Therefore, muscles on the body wall are not as
  strong as muscles in their appendages.

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Support and Movement

• In the water, salamanders move like fish.
• On land, they walk and it makes their body curve.
  
• Caecilians move like an accordion, pushing and
  pulling at the same time.
• Anurans have long hindlimbs that are modified for
  jumping.
• They also have connective tissue and muscles in
  the forelimbs that act as shock absorbers.

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Nutrition and the Digestive System

• Most adult amphibians are carnivores and eat a
  wide variety of invertebrates.
• Some anurans are more diverse.
• The main factors that determine what amphibians
  will eat are prey size and availability.
• Most larvae are herbivores and eat algae and
  other plant matter.

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Nutrition and the Digestive System

• Most amphibians locate their prey by sight and
  simply sit and wait for it to pass by.
• Water amphibians depend more on their sense of
  smell.
• Many salamanders use only their jaws to capture
  prey.
• Some salamanders and most anurans use their
  tongue and jaw in a flip-and-grab method.

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Nutrition and the Digestive System

• Amphibians have the first true tongue.
• Mucous and gland secretions make the tip of the
  tongue sticky.
• When prey comes within range, the tongue comes
  out, the tip traps the prey, and then trapped in
  the mouth.
• This whole process happens in about 0.5 seconds!
• The tongue then pushes the food toward the
  esophagus, and the eyes sink downward to help
  force the food.

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Circulation, Gas Exchange, Temperature Regulation

• Gas exchange occurs across the skin in
  amphibians, as well as in the lungs.
• So blood coming into the right side of the heart
  has almost as much oxygen as blood coming from
  the lungs.

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Circulation, Gas Exchange, Temperature Regulation

• In addition to a vascular system that circulates
  blood, amphibians also have a well-developed
  lymphatic system that helps return fluids and
  proteins to the blood vessels and also helps
  transport water across the skin.

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Circulation, Gas Exchange, Temperature Regulation

• Land animals expend much less energy exchanging
  gas than water animals do.
• This is because air contains 20 times more oxygen
  than water.
• There are 2 factors that permit amphibians to
  exchange gas across the skin their skin is very
  moist, and their skin also has a rich supply of
  capillaries.
• Gas exchange across the skin is called cutaneous
  respiration and can occur on land or in water.
• This ability allows frogs to spend the winter in
  mud at the bottom of a pond.

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Circulation, Gas Exchange, Temperature Regulation

• In salamanders, gas exchange can also occur in
  the mouth and pharynx.
• This is buccopharyngeal respiration.
• Most amphibians have lungs.
• Salamander lungs are very simple sacs.
• Anurans have divided lungs, providing more
  surface area for gas exchange.
• Amphibians larvae and some adults breathe using
  external gills.

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Circulation, Gax Exchange, Temperature Regulation

• Amphibians are ectothermic (they depend on
  external heat sources to maintain body
  temperature).
• When in the water, they will take on the
  temperature of the water.
• On land, their body temperature can be different
  from the environment.
• Temperature regulation is mainly behavioral.
• Many amphibians are nocturnal and remain in
  cooler burrows or under leaves during the hottest
  part of the day.
• They may warm themselves by basking in the sun.

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Nervous and Sensory Functions

• The nervous system of amphibians is similar to
  that of other vertebrates.
• Their brain has 3 sections forebrain, midbrain,
  and hindbrain.
• Amphibians have many sensory receptors on their
  skin.
• They also have a lateral line system similar to
  fish and this helps aquatic amphibians.

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Nervous and Sensory Functions

• Chemoreception is an important sense for many
  amphibians.
• Smell is used in mate recognition, detecting
  toxic chemicals, and in locating food.
• Vision is one of the most important senses for
  amphibians because they are primarily sight
  feeders, often responding to the movements of
  their prey.

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Nervous and Sensory Functions

• Some amphibian eyes are on the front of the head
  and some are more to the side.
• The lower eyelid is movable, and it cleans and
  protects the eye.
• Much of it is transparent and is called the
  nictitating membrane.

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Nervous and Sensory Functions

• Amphibians auditory system is an adaptation for
  living on land.
• It transmits both underground and airborne
  vibrations.
• Anuran ears are made up of tympanic membrane, a
  middle ear, and an inner ear.
• Anurans can screen out either high or low
  frequency sounds, depending on the situation.
• Salamanders have no tympanic membrane or middle
  ear.
• They have no mating calls, and the only sounds
  they hear are probably low-frequency vibrations.

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Excretion and Water Regulaton

• Amphibians do have kidneys.
• Their waste product is either ammonia or urea,
  depending on where they live.
• One of the biggest problems amphibians have is
  controlling the amount of water and salt in their
  body.
• In water, they must get rid of excess water while
  keeping essential ions.
• On land, they must conserve water.

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Excretion and Water Regulation

• They can not replace water in the usual ways.
• So they limit water loss by using behavior that
  avoids exposure to conditions that cause water
  loss.
• For example, many amphibians are nocturnal.
• Those that are active day AND night can rehydrate
  by going back in the water.
• Some amphibians have protective covering that
  reduce water loss.
• Others may form cocoons that cover the body
  during dormancy.
• They can also temporarily store water in the
  urinary bladder and lymph sacs.

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Reproduction, Development, Metamorphosis

• Amphibians have separate males and females.
• Fertilization is usually external, and because
  the developing eggs do not have protective
  covering, development must take place in moist
  habitats, usually water.

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Reproduction, Development, Metamorphosis

• Some anurans have nests on land that are kept
  moist by a foam covering or by being near water.

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Reproduction, Development, Metamorphosis

• The main exception to external fertilization are
  the salamanders.
• All caecilians have internal fertilization and
  about 75 have internal development.
• Amphibian development usually includes larval
  stages called tadpoles.
• Tadpoles are different from adults in how they
  breathe, how they move, and what they eat.
• This helps reduce competition between adults and
  larvae.

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Reproduction, Development, Metamorphosis

• Reproductive activity is often controlled by
  outside factors such as temperature (in temperate
  regions) and seasons (such as the rainy season in
  tropical regions).
• Courtship behavior helps individuals locate
  breeding sites and identify potential mates.
• Salamanders rely mostly on smell and vision clues
  in courtship and mating.
• Anurans, especially males, rely on sound.

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Reproduction, Development, Metamorphosis

• Sound production is mainly used in male anurans.
• These sounds will attract females and let other
  males know that a certain territory is taken.
• These sounds are species specific.
• Females respond by making the same call that
  indicates her willingness to mate.
• Release calls let a frog know that the partner is
  incapable of reproducing.
• Distress calls are associated with pain or with
  being seized by a predator.
• Sound production in frogs comes from the larynx
  and vocal cords.
• Males also have a vocal sac.

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Reproduction, Development, Metamorphosis

• Parental care increases the chance of any one egg
  surviving but requires a lot of energy from the
  parent.
• The most common form of care is protecting the
  egg clutch, usually done by either parent.
• Maternal care occurs in species with internal
  fertilization (salamanders and caecilians), and
  paternal care may occur in species with external
  fertilization (anurans).
• This care may involve providing oxygen to aquatic
  eggs, cleaning and/or moistening land eggs,
  protecting eggs from predators, or removing dead
  or infected eggs.

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Reproduction, Development, Metamorphosis

• Eggs may be transported if development occurs on
  land.
• Females of genus Pipa carry eggs on their back.
• Rheobatrachus females grow tadpoles in their
  stomach, and the young emerge from the females
  mouth.

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Reproduction, Development, Metamorphosis

• Metamorphosis is a series of abrupt structural,
  physiological, and behavior changes that
  transform a larva into an adult.
• Several conditions influence the time required
  for metamorphosis, such as crowding and food
  availability.
• Most changes, however, are controlled by
  hormones.

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Reproduction, Development, Metamorphosis

• Caecilian and salamander changes are minimal.
• They develop reproductive structures, lose their
  gills and caudal fin.
• Anurans have dramatic changes.
• Limbs and lungs develop, tail is reabsorbed, skin
  thickens, and noticeable changes in the head and
  digestive tract occur.

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AMPHIBIANS IN PERIL

• Frogs and salamanders are disappearing at an
  alarming rateand no one knows exactly why.
• Local events can affect populationsclear-cutting
  forests, mining, drilling, and urban sprawl
  destroy habitats.

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AMPHIBIANS IN PERIL

• Two other factors are thought to be affecting
  amphibiansacid deposits and UV radiation.
• Embryos are very susceptible to changes in the pH
  of their water.
• UV radiation also kills eggs and embryos.

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