Transcript Amphibian-Notes

AMPHIBIAN
NOTES
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Reproduction, Development,
Metamorphosis
• Some anurans have nests on land that are kept
moist by a foam covering or by being near water.
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.
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.
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.
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.
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 female’s
mouth.
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.
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.
AMPHIBIANS IN PERIL
• Frogs and salamanders are disappearing at an
alarming rate—and no one knows exactly why.
• Local events can affect populations—clear-cutting
forests, mining, drilling, and urban sprawl destroy
habitats.
AMPHIBIANS IN PERIL
• Two other factors are thought to be affecting
amphibians—acid deposits and UV radiation.
• Embryos are very susceptible to changes in the pH
of their water.
• UV radiation also kills eggs and embryos.