Transcript Chapter 31 Power Point

Chapter 31: Fishes and
Amphibians
Section 1: Fishes
What is a Fish?
• Fishes and other vertebrates have at some time
during their development a notochord, a
hollow dorsal nerve cord, and pharyngeal slits
• In most vertebrates, the notochord is replaced
during development by a backbone, or
vertebral column, which encloses and
protects much of the nerve cord
• In addition, most vertebrates have two sets of
paired appendages, a closed circulatory system
with a ventral heart, and either gills or lungs
for breathing
What is a Fish?
• Fishes can be defined as aquatic vertebrates that are
characterized by scales, fins, and pharyngeal gills
• There are so many fishes, living and extinct, that their
correct scientific classification is complicated
• For our purposes, we can say that the living fishes fall
into three main groups: jawless fishes, sharks and
their relatives, and bony fishes
– Sharks and their relatives are also known as
cartilaginous fishes because their skeletons are
made up of soft, flexible cartilage rather than bone
In ocean water deep below the
reach of sunlight live fishes
that sparkle with light
produced by their own body.
The lights on the viperfish
may serve to attract prey or
distract predators.
Representatives of the three main
groups of living fishes are shown
here. The lamprey is a parasitic
jawless fish. The blue-spotted
stingray is a venomous bottomdwelling cartilaginous fish. The
Potter’s angelfish, which is found
only in Hawaiian coral reefs, is a
bony fish.
Evolution of Fishes
• Fishes are the most primitive living
vertebrates
• The first fishes were odd-looking jawless
creatures whose bodies were covered with
bony plates
– Lived in the oceans of the late Cambrian
period (540 MYA)
– For over 100 MY, fishes retained the basic
armored jawless body plan
Evolution of Fishes
– Then, during the Ordovician and Silurian
periods, fishes underwent a major adaptive
radiation
• Jawless fishes – little armor
• Jawless fishes – no armor
–Still other were armored fishes that
possessed a feeding adaptation that
would revolutionize vertebrate
evolution: jaws
Evolution of Fishes
• Jawless fishes are limited to eating small
particles of food
• Jaws made it possible for vertebrates to nibble
on plants, munch on other animals, and defend
themselves by biting
• Also evolved pectoral and pelvic fins
– More control over their movement
Form and Function in Fishes
• Fishes have entered many environments and
evolved adaptations that enable them to
survive a tremendous variety of conditions
Feeding
• Every mode of feeding is seen in fishes
– Herbivores, Carnivores, Parasites, Filter
feeders, Detritus feeders
• A single fish may exhibit several modes of
feeding, depending on what type of food is
available
• The adaptations for feeding in fishes are often
remarkable
– Sawfish
– Parrotfish
Feeding
• Most fish do not chew their food
• Instead, they tear their food into chunks or
swallow their prey whole
Feeding
• From the mouth food passes through the
esophagus and into the stomach, where it is
partially broken down
• In many fishes, the food is further processed in
the pyloric ceca, which are located at the point
where the stomach and the intestine meet
– Secrete digestive enzymes and absorb
nutrients from the digested food
Feeding
• The intestine receives partially digested
food from the stomach and pyloric ceca and
completes the process of digestion and
nutrient absorption
• Any materials that remain undigested after
passing through the intestine are eliminated
through the anus
Fishes are adapted to many modes
of feeding. Some male anglerfishes
are parasites that are nourished by
the blood of their much larger
mates. Note the male attached to
the head of this female. The
parrotfish uses its “beak” to bite
off chunks of algae covered coral.
It digests the plant material and
passes the crushed coral dust
through its gut. The sawfish
slashes its way through schools of
fishes, then doubles back to devour
the dead or wounded prey.
The internal organs of a typical bony fish are seen
here.
Respiration
• Most fishes breathe with gills that are located
on either side of the pharynx
• Most fishes breathe by pumping water through
the mouth, over the gill filaments, and out
through slits in the sides of the pharynx
• A number of fishes have an adaptation that
allows them to survive in oxygen-poor water
or in areas where bodies of water often dry up
Respiration
• They have specialized organs that serve as
lungs by obtaining oxygen from the air
– Modified swim bladder
• Swim bladder is a gas filled sac that
controls the fishes buoyancy
In some fishes, such as sharks,
the gill chambers open to the
outside through a number of
slits. In other fishes, the gill
chambers empty through a
single opening that is covered
by a protective flap.
Internal Transport
• Typically have closed circulatory systems with
a heart that pumps blood around the body
• The heart consists of two muscular pumping
chambers
– Atrium
– Ventricle
• Pumps blood out of the heart into a
muscular vessel called the aorta
Almost all fish have a closed circulatory
system in which a two-chambered heart pumps
oxygen-poor blood from the body to the gills.
Oxygen-rich blood then travels from the gills to
all parts of the body.
Excretion
• Most fishes get rid of nitrogenous wastes in the
form of ammonia
• Some wastes diffuses through the gills into the
surrounding water
• Others are removed by the kidneys, which are
excretory organs composed of many tubules
that filter nitrogenous wastes from the blood
and concentrate them
• Kidneys help fishes control the amount of
water in their body
Response
• Fishes have a fairly well-developed nervous system
organized around a brain
• The most anterior parts of a fish’s brain are the
olfactory bulbs, which are connected by stalks to the
two lobes of the cerebrum
• Cerebrum – sense of smell, taking care of young,
exploring environment
• The optic lobes process information from the eyes
• The cerebellum coordinates body movements
• The medulla controls many internal organ functions
and maintains balance
Response
• Posterior to the brain is the spinal cord
• In cartilaginous and bony fishes, the spinal
cord is enclosed and protected by the
vertebral column
• Between each set of vertebrae, a pair of
spinal nerves exits the cord and connects
with internal organs and muscles
Response
• Most fishes have superbly designed sense
organs that collect information about their
environment
• Chemoreceptors
• Most fishes have ears inside their head, but
they cannot hear sounds well
– Detect vibrations
The brain of a
typical fish
has several
clearly visible
parts.
The sense organs in fishes
are highly developed. A
chimaera’s huge silvery
eyes enable it to see in the
permanent dark of its deepwater home. The lateral
line, which appears as a
series of tiny dots in the
pink stripe of the rainbow
trout, detects water
movements. Some fishes,
such as the elephant fish,
are able to detect electricity.
Reproduction
• Most fishes have separate male and female
sexes
• A number of fishes are born as males but
change to females as they grow older
• Many fishes are oviparous
– Lay eggs
• External fertilization
Reproduction
• Some species of fishes are ovoviviparous
– Young develop inside the mother’s body but
are not directly nourished by the mother’s
body
• Other species are viviparous
– Truly live-bearing
Some newly hatched
fishes, such as salmon,
are nourished by a yolk
sac on their belly.
Jawless Fishes
• Divided into two classes
– Lampreys and hagfishes
• Only vertebrates that do not have
backbones as adults
• Instead, their long, snakelike bodies are
supported by a notochord
Modern jawless fishes
are divided into two
classes: lampreys and
hagfishes.
Lampreys
• Filter feeders
• Adult’s head is completely taken up by a circular
sucking disk with a round jawless mouth in the
center
• Live by attaching themselves to fishes and
scraping away at the skin with their large teeth
and a strong tongue
• Then suck up tissues and body fluids
• Rarely kill their host, but do leave it in a
weakened condition with a large open wound
that is easily infected
Hagfishes
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Most primitive vertebrates alive today
Pinkish-gray wormlike bodies
4 – 6 short tentacles around the mouth
Lack eyes
Do have light detecting regions scattered
around their body
• Feed on dead and dying fish by using a toothed
tongue to scrape a hole into the fish’s side
Hagfishes
• Peculiar traits
– Secrete incredible amounts of slime
– Have six hearts
– Open circulatory system
– Tie themselves into knots
Sharks and Their Relatives
• Class Chondrichthyes
• Contains sharks, rays, skates, etc.
• All members have an endoskeleton made
entirely of cartilage
• 225 living shark species
– Curved tails, torpedo shaped bodies, and
rounded snouts
– Enormous number of teeth
• 3000 arranged in 6 – 20 rows
Sharks and Their Relatives
• Not all sharks attack people
• Some are filter feeders
• Others have flat teeth adapted for crushing
the shells of mollusks and crustaceans
• Each year more people are killed by
lightning than by sharks
Sharks and Their Relatives
• Rays and skates are adapted for living on the
ocean floor
– Flattened from top to bottom
– Swim by flapping their large wing like
pectoral fins
– Most reach a maximum length of about 1
meter
Cartilaginous fishes include sharks and rays. The wobbegong, or
carpet shark, is a bottom dweller that feeds primarily on fishes.
The leopard shark is one of the most attractive sharks. Its teeth are
adapted for crushing the shells of mollusks and crustaceans. The
underside of some rays seems to have an almost human face.
Bony Fishes
• Class Osteichthyes
• More species in this class than in any other
vertebrate class
• About 40% of all vertebrates are bony
fishes
• Somewhere between 15,000 and 40,000
species alive today
Bony Fishes
• Almost all bony fishes belong to the enormous
group called the ray-finned fishes
• Includes everything from guppies to groupers,
salmon, and eels
• The name refers to the thin bony spines, or
rays, that are connected by a thin layer of skin
to form the fins
• These fins are adapted to a wide variety of
functions
Bony Fishes
• Only seven living species of bony fishes are not classified
as ray-finned fishes
• These are the lungfishes and the coelacanth
• These fishes are of interest because they give us an idea of
what the lungs and limbs may have been like in the
ancestors of terrestrial vertebrates
• The six species of lungfishes alive today are found in
Australia, Africa, and South America
• When water is available, lungfish use their gills to
eliminate carbon dioxide, but they get most of their
oxygen by gulping air into a simple sac that functions as a
lung
• During the dry season, lungfish burrow in the mud and
enter a dormant state
Bony Fishes
• The single species of coelacanth alive today is the only
surviving member of the lobe-finned fishes
• Unlike ray-finned fishes, which have many bones in the
bases of their fins, coelacanths have few bones in their
fin bases
• Attached to those bones are a few large rays that form
the fins
• Ancient lobe-finned fishes seemed to have lived in
swampy areas where shallow pools alternated with mud
flats and sand bars
• The modern coelacanth lives in water about 70 to 400
meters deep in a relatively small area of ocean off the
western coast of Africa
Bony Fishes
• Coelacanths were thought to have disappeared
with the dinosaurs about 70 million years ago
• In 1938, however, fishermen sailing in the
ocean off the coast of Africa caught a
coelacanth
• Scientists were enormously excited to find
living coelacanths because these animals
represent a fascinating piece of evolutionary
history
– The closest thing we known of to the
ancestors of all land vertebrates
How Fishes Fit into the World
• Fishes are vital parts of many biological
systems
• For many birds and mammals fishes are
important foods
• As predators and herbivores, fishes help
control the populations of the organisms they
eat
• Since prehistoric times, humans have caught
fishes for food and recreation
• For at least 4000 years, humans have also
raised fishes in artificial ponds
Bony fishes come in a wide variety of
forms and colors. The porcupine fish can
inflate itself into a prickly ball when
threatened. The moray eel has a narrow
snakelike body. The bright colors of
angelfish may be a means of
communication within its species. The
hawk fish's narrow snout enables it to pluck
bits of food from crevices.
A few fishes manage quite
nicely out of water for
brief periods of time.
African lungfishes get
most of their oxygen from
the air, which they gulp
into a simple sac that
serves as a lung.
Mudskippers climb out of
the water onto logs and
rocks. As you can see, the
mudskipper’s bulging
eyes are quite mobile,
enabling it to appear as if
it has eyes on the back of
its head.
Chapter 31: Fishes and
Amphibians
Section 2: Amphibians
Amphibians
• About 4,000 living species
• Amphibians are the smallest major group
of vertebrates
• Range in size from tiny tropical tree frogs
1cm long to enormous salamanders 170
cm long
• Some have long tails and walk on four
legs
• Others have no tails and leap from one
place to another with large hind legs
Amphibians
• They are descendents of ancestral
organisms that evolved some of the
adaptations necessary for life on land
• Nearly all of them are restricted to moist
areas, and most of them must return to
water to breed
Representatives of the three
orders of living amphibians
– salamanders, frogs and
toads, and legless
amphibians – are shown
here.
What Is an Amphibian?
• The name amphibians refers to the double
life that most amphibians lead
– Larvae are fishlike aquatic animals that
breathe through gills
– Adults are terrestrial carnivores that
breathe through lungs and skin
• Amphibians are strongly tied to the water
because their eggs do not have a shell
What Is an Amphibian?
• Their skin does not have scales or any other
protective covering
• The skin of almost all adults is used in respiration
and must remain moist
• Amphibians can be defined as vertebrates that
are aquatic as larvae and terrestrial as adults,
breathe with lungs as adults, have a moist skin
that contains many glands, and lack scales and
claws
Most amphibians spend the
first part of their life in
water as gilled larvae. As
adults, they usually live on
land.
Evolution of Amphibians
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Amphibians first appeared about 360 million years ago
Amphibians evolved from lobe-finned fishes
Making the transition from water to land was not easy
Because natural selection favored individuals that were
better able to live on land, early amphibians evolved in
ways that went above many problems
– Bones became stronger
– Ribs formed a cage to protect internal organs
– Ears were added to the lateral line system
– Mucous glands, eyelids, and other structures that
protect sense organs from drying out developed
Evolution of Amphibians
• When amphibians started crawling onto land,
they entered an environment nearly empty of
animal life
• Any vertebrates whose legs and lungs
allowed them to spend time on land had lots
of food and no competitors
• This was short-lived
• Climate changes ultimately caused many of
the low, swampy amphibian habitats to
disappear
• Most of the amphibian groups became
extinct about 245 million years ago
Form and Function in
Amphibians
• Living amphibians have evolved many
adaptations that help them overcome the
problems of living both in water and on
land
• As we examine the essential life functions
in amphibians, we will focus on frogs
Feeding
• Tadpoles are typically filter feeders or herbivores
• Tadpoles have to grow quickly
– Those that lag behind may starve or die if their puddle
dries out
• Adult amphibians are almost entirely carnivorous
• From the mouth, food slides down the esophagus into the
stomach
• The stomach connects with the small intestine
• The small intestine leads to the large intestine, or colon
• At the end of the large intestine is a muscular cavity
called the cloaca, which stores wastes until they are
expelled
Respiration
• Adults typically breathe using lungs, mouth cavities, and
skin
• The lungs are reasonably well developed
– Capillaries
• The lining of the mouth cavity and the body skin are thin
and richly supplied with blood vessels
• Most carbon dioxide is removed through the skin
• Frogs cannot inhale and exhale as we do
– They fill their mouth cavity with air, close their mouth,
and force air back through an opening called the glottis
into the lungs
• Frogs can also direct some of the air they take in to a pair of
vocal sacs
As air moves between
the vocal sac and
mouth in male frogs it
causes the vocal
cords to vibrate.
Although the
resulting sounds may
not be music to
human ears, a female
frog finds them quite
attractive.
Internal Transport
• Circulatory system is a double loop
– First loop carries oxygen-poor blood from the
heart to the lungs and takes oxygen-rich blood
from the lungs back to the heart
– The second loop transports oxygen-rich blood
from the heart to the rest of the body and oxygenpoor blood from the body back to the heart
• 3 chambered heart
– Left atrium, right atrium, and ventricle
• Tadpoles have two chambered hearts and
single-looped circulatory systems
Excretion
• Amphibians use kidneys to eliminate wastes
from their bloodstream
• The kidneys are dark colored oval structures
that lie against the dorsal part of the body wall
• The excretory product of the kidneys – urine –
travels through tubes called ureters into the
cloaca
• From there it can be passed directly to the
outside or it may be stored in a small urinary
bladder
Response
• Well developed nervous and sensory systems
• Large eyes with a nictitating membrane
– Protects from damage under water
– Kept moist on land
– Located inside the regular eyelid
• Ears have no external sound collectors
– Hearing is vital to their survival and reproduction
• Respond to adverse conditions in many different ways
– Being in a sheltered spot, dormant state
– Camouflage
– Distasteful or toxic chemicals
– Warning coloration
The brain of a frog
has the same basic
parts as that of
other vertebrates.
Frogs escape predators in
many ways.
Reproduction
• When frogs reproduce, the male climbs onto
the female’s back and squeezes
• In response to this, the female releases as many
as 200 eggs
• The embryos are surrounded with a sticky
substance that attaches the egg mass to
underwater plants and nourishes the
developing embryos
• The eggs typically hatch into tadpoles after 1 –
3 weeks
• Not all amphibians have external fertilization
Reproduction
• Parental care in amphibians varies greatly
• Some frogs incubate their young in their
mouth, vocal sac, or stomach
• Some have special sacs to store the eggs
• In certain tree frogs, tadpoles cling to their
parent’s back with a sucker like mouth and
are carried between pools of rainwater that
collect among the leaves of certain plants
Salamanders
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These amphibians keep their tails even as adults
Both adults and larvae are carnivores
Most modern salamanders are about 15cm long
Most hatch as fully aquatic larvae with gills
As adults they live in moist woods, where they
tunnel under rocks and rotting logs
• Some salamanders never lose their gills and live in
water all their life
• Some newts switch back and forth between water
and land
Salamanders are usually
terrestrial as adults.
However, certain species of
salamanders, known as
newts, are terrestrial only
during an immature phase
known as red eft.
Frogs and Toads
• Of the two, frogs are most closely tied to water
• Frogs spend much of their time in or near ponds
and streams
• Adult toads, on the other hand, often live in moist
woods
• These animals burrow deep into moist soil and
press their skin against the walls of their burrows
• Many toads and frogs produce potent toxins
• One species of poison arrow frog produces a toxin
so powerful that 0.00001 gram can kill an adult
human
How Amphibians Fit into the
World
• Prey on insects
• Frog legs are a delicacy in some cultures
• Native hunters tip their arrows with toxins
to kill large animals
• Researchers are studying the action of
poison arrow frog toxins for clues to the
way the nervous system works
• Studies of regeneration