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AMPHIBIANS

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Title: AMPHIBIANS


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  • AMPHIBIANS

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  • Amphibians
  • Amphibians are tetrapods (four foot)! The name is
    derived from the presence of four muscular limbs
    and feet with digits!

3
  • Amphibians occur on all continents except
    Antarctica!
  • Modern amphibians belong to three orders!

4
  • Order Caudata salamanders
  • Order Anura - frogs and toads
  • Order Gymnophiona caecilians

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  • Order Caudata
  • They posses a tail throughout life!

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  • Most terrestrial salamanders live in moist forest
    floor litter and have aquatic larva! A number
    live in caves!

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  • Members of the family Salamandridae are commonly
    called newts! They spend their lives in water and
    often have a caudal fin! Range in size from a few
    centimeters to 1.5 meters (Andias japonicus)!

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  • The largest in North America is the hellbender
    (Cryptobranchus alleganiensis) which grows to
    about 65 cm!

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  • Most salamanders have internal fertilization!
    Males produce a spermatophore which they deposit
    onto a leaf! The female picks it up and places it
    in a special pouch called a spermatheca and
    fertilization happens!

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  • Larva are similar to adults only smaller! Many
    salamanders undergo incomplete metamorphosis and
    are paedomorphic! (They become sexually mature
    while still showing larval characteristics!)

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  • Order Gymnophiona caecilians
  • Wormlike burrowers that feed on invertebrates in
    the soil! They appear segmented because of folds
    in the skin that cover the separations between
    muscle bundles!

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  • Fertilization is internal in caecilians!
  • Order Anura
  • Includes about 3,500 species of frogs and toads!

23
  • Adults lack tails and caudal vertebra fuse into a
    rodlike structure called a urostyle!
  • Hindlimbs are long and muscular and end in webbed
    feet!

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  • Fertilization is almost always external and eggs
    usually are aquatic!
  • Larval stages called tadpoles have well developed
    tails!

25
  • Unlike adults, the larva are herbivores and
    posses a beaklike structure used in feeding!

26
  • The term toads usually refers to anurans with
    relatively dry and warty skin that are more
    terrestrial than other members of the order!
  • True toads belong to the family Bufonidea!

27
  • External Structure And Locomotion!
  • Their skin is designed to protect against
    infective microorganisms, ultraviolet light,
    desication, and injury!

28
  • It also functions in gas exchange, temperature
    regulation, and the absorption and storage of
    water!
  • Amphibians have no scales, feathers, or hair!

29
  • The skin is highly glandular and its secretions
    aid in protection! They help keep the skin moist!
  • They produce toxic chemicals that discourage
    potential predators!

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  • The skin is mostly smooth but some have warts,
    usually as the result of keratin deposits!

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  • Chromatophores are specialized cells in the skin
    that are responsible for skin color and color
    changes!

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  • Compared to fish, the amphibian skull is
    flattened, smaller, and have fewer bony elements!
  • Changes in the jaws and jaw muscles allow
    terrestrial vertebrates to crush prey held in the
    mouth!

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  • The backbone of amphibians is modified to provide
    support and flexibility on land!
  • Unlike fish, amphibians have a neck!

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  • The first vertebra is the cervical vertebra which
    moves against the back of the skull and allows
    the head to nod vertically!
  • The last trunk vertebra is the sacral vertebra!

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  • It anchors the pelvic girdle to the vertebral
    column to provide increases support!
  • A ventral plate of bone called the sternum
    supports the forelimbs and internal organs. It is
    reduced or absent in frogs and toads!

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  • The pelvic girdle of amphibians consists of three
    bones (the ilium, ischium, and pubis) that attach
    pelvic appendages to the vertebral column!

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  • Long hindlimbs and powerful muscles form an
    efficient lever system for jumping in anurans!

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  • Nutrition and the Digestive System!
  • An adult bullfrog will prey on small mammals,
    birds and other anurans!
  • Most larva are herbivorous and feed on algae and
    other plant matter!

40
  • Most salamanders use only their jaws to capture
    prey but anurans use their tongue and jaws to
    capture prey. Amphibians are the first animals we
    have studied to have a tongue!

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  • Gas Exchange
  • Terrestrial animals spend much less energy moving
    air across gas exchange surfaces than do aquatic
    organisms because air contains 20 times more
    oxygen than water!

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  • Amphibian skin is moist and richly supplied with
    capillary beds! These two factors permit the skin
    to function as a respiratory organ! Gas exchange
    across the skin is called cutaneous respiration!

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  • This can occur on land or in water!
  • In salamanders 30 90 of respiration can occur
    across the skin!
  • Gas exchange can also occur across the surface of
    the mouth and pharynx!

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  • This is called buccopharyngeal respiration and
    account for about 7 of respiration!
  • The amount of gas exchange in these two methods
    cannot be increased when metabolic rate increases!

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  • Temperature Regulation
  • Amphibians are ectothermic (cold blooded)! They
    depend on external heat sources to maintain body
    temperature!
  • Animals in water loose heat very quickly!

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  • When amphibians are in water they take on the
    temperature of the water they are in! On land
    they can regulate their temperature more easily!

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  • Temperature regulation is mainly behavioral!
  • Many are nocturnal!
  • Some warm themselves by basking in the sun,
    especially after eating because it speeds up
    digestion!

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  • Nervous And Sensory Functions
  • similar to other vertebrates!
  • The brain is divided into three regions
    forebrain, midbrain, hindbrain!

53
  • Forebrain contains the olfactory centers and
    the regions that regulate color changes!
  • Midbrain assimilates sensory information and
    initiate motor responses!

54
  • The hindbrain functions in motor coordination and
    in regulating heart rate and respiration!
  • Olfaction is used in mate recognition as well as
    in detecting food and chemicals!

55
  • Vision is one of the most important senses in
    amphibians because they are primarily sight
    feeders often responding to the movement of their
    prey!

56
  • The lower eyelid is moveable and it cleans and
    protects the eye! Most of it is transparent and
    is called the nictitating membrane! When the
    eyeball retracts into its socket the nictitating
    membrane is drawn up over the cornea!

57
  • There are receptors called rods and cones in the
    retina! Because cones are associated with color
    vision in some vertebrates they can probably see
    some wavelengths of light!

58
  • The ears of aunurans consists of a tympanic
    membrane, a middle ear, and an inner ear! The
    tympanic membrane receives airborne vibrations
    and transmits them to the middle ear!

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  • Next to the tympanic membrane is a bone called a
    stapes or columella which transmits the
    vibrations of the tympanic membrane into the
    inner ear!

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  • Excretion and Osmoregulation
  • The nitrogenous waste products that amphibians
    excrete is either ammonia or urea!
  • They produce large amounts of very dilute urine!

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  • Adult amphibians do not replace water by
    drinking, instead they limit water loss by
    behavior that prevents desiccation! Many are
    nocturnal, or burrow, or live in areas of high
    humidity!

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  • Some make a protective cocoon from the outer
    layers of the skin that detaches and becomes
    paper-like!

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  • REPRODUCTION, DEVELOPMENT, and METAMORPHOSIS!
  • Amphibians are dioecious!

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  • Fertilization is usually external and because the
    developing eggs lack any resistant covering
    development must occur in water!

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  • In a few species larval stages occur in the egg
    and the babies emerge looking like miniature
    adults!

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  • All others produce spermatophores and
    fertilization is internal!

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  • Amphibian tadpoles often differ from the adults
    in the way they breath, how they move, and what
    they eat! These differences reduce competition
    between adults and larvae!

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  • VOCALIZATION
  • Sound production is primarily a reproductive
    function of the males!
  • They produce advertising calls, reciprocation
    calls, release calls, and distress calls!

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  • The sound production apparatus of frogs consists
    of the larynx and vocal cords. The males also
    have a vocal sac!

73
  • Air from the lungs is forced over the vocal cords
    and cartilages of the larynx causing them to
    vibrate. Muscles control the tension of the vocal
    cords and regulate the frequency of the sound!

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  • Vocal sacs act as resonating structures and
    increase the volume of the sound!

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  • PARENTAL CARE
  • The most common form of parental care in
    amphibians is the attendance of the egg clutch by
    either parent!

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  • METAMORPHOSIS Metamorphosis is a series abrupt
    structural, physiological, and behavioral changes
    that transform a larva into an adult!

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  • Metamorphosis is under the control of
    neurosecretions of the hypothalamus, the
    pituitary gland, and the thyroid gland!

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  • AMPHIBIANS in PERIL
  • Frogs and salamanders are disappearing very
    quickly. One reason is loss of habitat by cutting
    forests, mining, industrial development and
    agriculture.

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  • An increase in U.V rays in the 280 320 nm range
    has killed many embryos .
  • Amphibians are especially susceptible to changes
    in the pH of water. A pH lower than 5 will kill
    them. This is caused by acid rain.

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  • Pollutants that contribute to acid rain and the
    depletion of the ozone shield of the earth may be
    partly responsible for the disturbing reduction
    in amphibian populations.

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  • Chytrid, a fungus, first seen in the 1980s has
    been detected on at least 385 species of
    amphibians from 36 countries and is likely
    responsible for over 100 species extinctions.
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