Transcript Topic 11 Amphibians - Plattsburgh State Faculty and Research Web

Earliest amphibians
 The
earliest are the labyrinthodonts, which
included Icthyostega and Acanthostega.
 During
the Carboniferous a couple of
major lineages of labyrinthodonts arose:
the Temnospondyls and the
Anthracosaurs.
Anthracosauria and
Temnospondyls
 The
Anthracosauria and the
Temnospondyls were both diverse groups
and many were very large being several
meters long.
 They
looked a bit like large, sprawling
reptiles with scaly skin and big heads.
Poterogyrinus an Anthracosaur
http://upload.wikimedia.org/wikipedia/
commons/thumb/2/2c
/Proterogyrinus_DB.jpg/260px-Proterogyrinus_DB.jpg
Seymouria: an Anthracosaur
http://www.prism.gatech.edu/
~gh19/b1510/tetra.gif
A small carboniferous temnospondyl and a scorpion
http://www.hmnh.org/galleries/permocarboniferous/temnospondyl.gif
Eryops: a temnospondyl http://comenius.susqu.
edu/bi/202/
animals/DEUTEROSTOMES/
vertebrata/eryops.jpg
Anthracosauria and
Temnospondyls

Both groups left modern descendants behind.
 The Anthracosauria gave rise to the amniotes in
the late Carboniferous, but the rest of the group
became extinct in the Permian.
 There were diverse temnospondyl groups during
the Carboniferous and Permian periods, but
except for one lineage (the Lissamphibia: the
modern amphibians) they became extinct by the
end of the Triassic.
Lissamphibia

The Lissamphibia includes all three modern groups of
amphibians. All three have smooth skin, hence their
name (“Liss” means smooth.).

The oldest fossil salamanders date to the Jurassic
(about 145 mya).
The oldest true frog fossils date to 190mya, but froglike
vertebrates are known from 200 mya.
Caecilian fossils are scarce but the oldest known are
from 195 mya. These had well-developed eyes and
small functional limbs (unlike modern forms).


Callobatrachus sanyanensis: fossil frog from Lower Cretaceous.
http://images.google.com/imgres?imgurl=http://www.fossilmuseum.net/Fossil-Pictures/
Frogs/Callobatrachus/Callobatrachus-sanyanensis1024.jpg&imgrefurl=
http://www.fossilmuseum.net/Fossil-Pictures/Frogs/Callobatrachus/
Callobatrachus-sanyanensisb.htm&usg=__mJ8yZDNglWYiMrS7kPPE3NHV794=&h=
768&w=1024&sz=146&
hl=en&start=6&um=1&tbnid=I7dMno_ZrUhMuM:&tbnh=113&tbnw=150&prev=/
images%3Fq%3Dfossil%2Bfrog%2B%2Bimages%26hl%3Den%26sa%3DG%26um%3D1
Lissamphibia
 The
evolutionary relationships between
the three modern groups of the
Lissamphibia are not clear and a lack of
fossils has hindered an understanding of
their relatedness and evolutionary origins.
Class Lissamphibia
 The
amphibians are represented by about
4800 hundred species divided into three
orders.
 Urodela “tailed ones”: salamanders
 Anura: “tailless ones” frogs, toads.
 Gymnophiona (“naked snake”; previously
Apoda “legless ones”) caecilians.
Eastern Mud salamander
http://fwie.fw.vt.edu/VHS/amphibians/salamanders/eastern-mud-salamander/
Eastern_Mud_Salamander_Pseudotriton_mlr.jpg
http://upload.wikimedia.org/
wikipedia/commons/6/66/
Caecilian_wynaad1.jpg
Caecilian
http://www.gregboettcher.com/as/science/classification/images/caecilian.jpg
Red-eyed Tree frog
http://www.frogsite.org/pic/Redeyed_Tree_Frog.jpg
Amphibian skin
 Amphibians
lack scales and are
characterized by a moist permeable skin.
 This limits the environments in which they
typically can live as they are constrained
by the threat of water loss.
 Typically
they inhabit wet or damp habitats
where the humidity is high (e.g., ponds.
forest floors in leaf litter).
Amphibian skin

Many anurans and salamanders absorb moisture from
the soil or other substrates through their skin.

A number of anurans have a specialized region of skin
on the ventral surface around the pelvis (the “seat patch”
or “pelvic patch”) that is highly permeable to water and
allows water to flow rapidly into a dehydrated animal.

In dehydrated Giant Toads (Bufo marinus) the pelvic skin
is 6X as permeable to water as skin from the pectoral
region.
Mucous gland and poison glands

Amphibian skin often contains mucous glands
and granular (poison) glands.

Mucous glands continuously produce
mucopolysaccharides, which help keep the skin
moist and able to function in gas exchange
when the animal is out of water. The mucus
may also have anti-predator benefits as it makes
the animal slippery and difficult to grip.
Poison glands
 Granular
glands in many amphibians
produce noxious and sometimes toxic
secretions.
 These
glands are often grouped together
and give the skin a textured appearance.
The warts and parotid glands of toads and
the dorsolateral ridges of Rana frogs are
good examples.
Poison glands
 Toxin-secreting
granular glands are
widespread in anurans, but also occur in
some salamanders and caecilians.
 Toxins
include vasoconstrictors, hemolytic
substances, neurotoxins and
hallucinogens. Their effects range from
localized irritation to hypothermia,
convulsions, and paralysis.
Poison glands
 Newts
of the genus Taricha produce a
neurotoxin that is present in high
concentrations and a single individual
produces enough toxin to kill 25,000 mice.
 The
salamander Bolitoglossa rostrata
produces skin secretions that may
paralyze and sometimes kill garter snakes
that attempt to eat them.
Poison dart frogs

Several genera of brightly colored Neotropical
frogs (Dendrobates, Phyllobates, and
Epipedobates) produce highly toxic steroidal
alkaloids in their skin.

The alkaloids affect both the muscular and
nervous systems causing muscles to remain
contracted and blocking nerve transmissions,
which can result in cardiac arrest and death.
Green and Black Poison Dart Frog
http://www.shoarns.com/frog.jpg
Poison dart frogs

These frogs are very small (rarely more than 2” long),
but just one frog produces enough toxin to kill several
people.

Several tribes of Colombian Indians use the toxins of
Phyllobates frogs to tip the darts for their blowguns.

The toxin is extracted by impaling the frogs on sticks and
holding them over a fire, which causes the toxin to seep
out so it can be collected.

The tips of darts are then dipped in the poison, allowed
to dry and used to kill birds and small mammals.
Medical applications of skin
secretions
 There
have been a variety of
investigations into the medical benefits of
various amphibian skin secretions.
 For
example a powerful painkiller called
epibatidine (200X more powerful than
morphine) has been isolated from a poison
dart frog.
Medical applications of skin
secretions

In addition, a bacteria-killing antibiotic peptide
called magainin has been isolated from the skin
of the African clawed frog.
 This and similar peptides are released to the
skin when it is injured and kill a wide range of
bacteria as well as parasites, fungi and certain
viruses.
 Unlike most antibiotics, which disable important
bacterial enzymes, these peptides disrupt
bacterial membranes punching holes through
them so the contents leak out.
Gas exchange

The moist skin is used extensively for gas
exchange and some salamanders and one
species of caecilian have lost their lungs over
evolutionary time and depend exclusively on gas
exchange across the skin and oral cavity.

To enhance gas exchange the skin in many
species (e.g. hellbenders) is highly folded and
heavily vascularized.
Eastern Hellbender
http://fwie.fw.vt.edu/VHS/amphibians/salamanders/eastern-hellbender/hellbenderMikePinder.jpg
Gas exchange

Gas exchange also takes place via lungs and gills (in
larvae).

Amphibians use a force pump mechanism to get air into
their lungs. Air enters the oral cavity through the nostrils,
the nostrils close and the floor of the mouth is raised
forcing air into the lungs and prevented from escaping by
a sphincter muscle.

Some frogs and toads can repeatedly use this
mechanism to inflate their lungs greatly and make
themselves appear large and less attractive to a
predator.
Gills
 Larval
amphibians breathe using external
gills. In anuran tadpoles the gills are
concealed behind a flap of tissue and
water flows through the mouth across the
gills and out of a spiracle.
 When
anuran tadpoles metamorphose into
adults the gills are reabsorbed.
Gills

In larval salamanders and caecilians the gills are
exposed and project from the sides of the head.

Most species lose their gills when they mature
but some retain them into adulthood (neotony).
For example, the aquatic salamanders Necturus
and Cryptobranchus possess both gills and
lungs. These species usually air breathe only
when oxygen levels in the water are low or when
recovering from strenuous activity.
Larval Tiger Salamander
http://www.axolotl.org/images/tiger/tiger_larva.jpg
Feeding

All adult amphibians are carnivorous and
amphibians eat anything they can catch and
swallow.

Because amphibians generally swallow their
prey whole, head size limits prey size.

Frogs of the genera Lepidobatrachus and
Ceratophrys which mainly eat other frogs have
enormous heads relative to their body size.
Amazon Horned Frog
http://www.itsnature.org/wp-content/uploads/2008/02/amazon-horned-frog.jpg
Feeding
 Most
amphibians have small, identical
teeth (homodont dentition), which are
found on both the palate and jaw.
 The
function of the teeth is to grasp and
hold prey not to chew it.
Tongue protrusion

Most amphibians possess a sticky tongue and many can
rapidly evert it to catch prey.

In salamanders of the genus Hydromantes the tongue
can be extended 80% of the body length (about 6cm). A
ballistic mechanism is used to fire the tongue out and it
is retracted by a series of muscles.

When the tongue is everted the whole tongue skeleton
leaves the mouth. Hydromantes is the only vertebrate
that is known to shoot a part of its skeleton as a missile.
Hydromantes salamander shooting its tongue to catch a housefly
http://autodax.net/tngphoto.jpg
Tongue protrusion
 In
some anurans, such as Rana and Bufo,
the tongue is very protrusible.
 It is attached to the front of the mouth and
flipped out using muscular action so that
the rear upper surface of the retracted
tongue becomes the front lower surface of
the extended tongue.
 Caecilans have rudimentary tongues that
cannot be everted.
http://www.ourclassweb.com/projects/webquest_frogs_tongue.jpg
Bullfrog feeding clip
 http://www.youtube.com/watch?v=wXqK5
QulbJ8&feature=results_video&playnext=1
&list=PLF0F6BFDE4C37D6F7
Reproduction
 The
word amphibian means “two lives”
and is a reference to the fact that frogs go
through metamorphosis from a tadpole
stage.
 In
most anurans fertilization is external.
The male grips the female and fertilizes
the soft eggs as the female sheds them
from her body.
Reproduction

Amphibian eggs do not have a hard shell and
dry out quickly if not kept in a moist environment.

Many species lay their eggs directly in water or
on the undersides of leaves over water so the
larvae fall in when they hatch.

Others show more parental care and brood eggs
in (depending on the species) the mouth,
stomach or pressed into soft skin on their backs.
Figure 25.04
Reproduction
 Eggs
in frogs develop into tadpoles that
have a fishlike tail and external gills.
 As
the tadpole develops, often very quickly
in a race against time to escape a pool
before it dries up, limbs develop, the tail
shortens by reabsorption and the gills are
lost as the tadpole metamorphoses into a
miniature frog.
Figure 25.26
Salamander reproduction

Unlike frogs most salamanders (>90%) use internal
fertilization.

An intromittent organ is not used. Instead males
produce packets of sperm called spermatophores.

Depending on the group of salamander, males may
insert the spermatophore into the female or the female
may pick it up with her cloaca and then use the sperm to
fertilize eggs as they pass out of her body.
Salamander spermatophores
http://www.wildlife.state.nh.us/Wildlife/Nongame/salamanders/
salamander_images/spermatophore2-Marchand.jpg
Reproduction

Unlike frogs, the young of most terrestrial
salamanders develop from eggs into a larva that
looks like a smaller version of the adult, but
which has gills, which are lost at metamorphosis.

The most terrestrial salamanders, the lungless
plethodontids, have evolved young that hatch
from the egg as miniature versions of the adult
and there is no aquatic larval stage.
Reproduction

Other salamanders lay their eggs in water. Eggs
may be laid singly or in clumps.

These eggs develop into larvae that are
miniature versions of the adults, but they have
external gills.

In terrestrial species larvae transform into a
juvenile stage called an eft and when sexually
mature these return to water to breed.
Figure 25.08
Caecilian reproduction

In caecilians fertilization is internal (males
possess an intromittent organ) and they employ
a variety of developmental strategies.

Some species are oviparous with aquatic larvae,
others are oviparous, but the young develop
directly into terrestrial young. In many cases,
the mother will brood the eggs until they hatch.
Figure 25.05
Many caecilians lay their eggs in the mud near water,
but some caecilians brood their eggs in burrows.
Caecilian reproduction
 However,
the majority of caecilians are
viviparous (about 75%) and matrotrophic
(young obtain nutrition from the mother).
 Newborn
caecilians are 30-60% of the
length of their mother and a litter may
include 9 or 10 babies, so mothers clearly
invest heavily in their offspring.
Caecilian with young
http://www.abdn.ac.uk/~nhi708/
classify/animalia/chordata/amphibia/
apoda/caecilian.jpg
Caecilian reproduction

Egg yolk provides the initial nourishment for
viviparous young, but further growth comes from
feeding directly on the mother.

Viviparous forms have teeth (shed after birth),
which they use to scrape the epithelial lining of
the oviduct to obtain nutrition. The epithelium
secretes a thick, creamy substance that has
been called uterine milk that the young consume
along with epithelial tissue.
Caecilian reproduction
 A Kenyan
species of caecilian
Boulengerula taitana feeds its young in a
different, but similar way.
 These
young are born relatively
undeveloped and feed by peeling off
layers of their mother’s skin, which
contains lipid-filled vesicles.
Courtship and mate selection in
amphibians
 A variety
of courtship activities occur in
amphibians.
 In
anurans most breeding occurs at night
and males call to attract females.
 Females assess male quality on the basis
of the calls (e.g. larger males have deeper
calls) and choose the highest quality
males.
http://www.arkive.org/media/5A/5A3F66F4-5FA6-4C81-9B92-0D29A942F58D/
Presentation.Large/photo.jpg
Courtship and mate selection
 Calling
is energetically expensive and only
the healthiest males can call for long
periods.
 Lower quality males unable to attract a
female to themselves may adopt other
tactics such as gathering around calling
males and attempting to intercept females
attracted by the caller.
Courtship and mate selection
 Many
salamanders defend territories and
those that can control high quality
territories (usually the larger males) attract
the most mates.
 Females
are also attracted to the fecal
smell of male salamanders that have
consumed high quality diets.
Order Urodela
 There
are about 550 species of
salamanders. They have an elongate body
and long tail and most live on land.
 Salamanders
are almost entirely confined to
the Northern Hemisphere with only a few
species occurring in northern South
America.
Order Urodela
 The
greatest diversity of salamanders
occurs in North and Central America and
more species of salamander occur in
Tennessee than in Europe and Asia
combined.
Order Urodela

Salamanders have an elongate body and long tail and
most live on land.

Apart from a few completely aquatic species, salamanders
have four functional limbs and use a walk that combines
the lateral bending of fish with leg movements.

Because the legs project to the sides (instead of being
under the body as in e.g. reptiles) salamanders sprawl and
the belly often rubs against the substrate.

This form of movement is probably similar to that used by
the earliest tetrapods.
Order Urodela
 Most
salamanders are <15cm long, but
some aquatic forms are bigger, the largest
being the Japanese Giant Salamander
(1.5 meters long).
Japanese Giant Salamander
http://farm3.static.flickr.com/2387/2368605286_95f46c45c4.jpg
Paedomorphosis

Paedomorphosis is widespread among
salamanders and in a number of families only
paedomphic forms occur.

These animals retain as adults larval
characteristics.

These can include a lack of eyelids, a lateral line
system, larval tooth and bone patterns and, in
some instances, external gills.
Paedomorphosis
 Paedomorphic
forms include the
widespread hellbenders and mudpuppies,
which occur in North American streams
and rivers.
Cave dwelling salamanders
 Several
groups of salamanders have
become specialized for living in caves.
 Forms
that live in cave mouths tend to
retain fully metamorphosed adults, but
species adapted to the darkest parts of
caves are paedomorphic.
Cave dwelling salamanders
 The
most specialized cave dwellers
include the Texas Blind salamander and
the European Olm.
 These
are both white, blind and possess
external gills and flattened snouts that help
them reach food under stones.
Texas Blind Salamander
http://pubs.usgs.gov/circ/circ1293/images/Figure8_large.jpg
Order Anura
 The
frogs and toads are by far the largest
group of amphibians with more than 4000
described species.
Order Anura
 Anurans
have a large worldwide
distribution despite being tied to water for
reproduction, having a moist permeable
skin and being ectothermic, which means
they cannot occupy polar or sub-polar
environments.
 They
are specialized for jumping and as
adults lack a tail.
Specializations for jumping

The hind legs are very enlarged and elongated.
 The vertebral column is short and the vertebrae are
braced by zygapophyses that limit lateral bending.
 The pelvis is solidly attached to the vertebral column and it
has been greatly modified and strengthened.
 The ilium has been elongated and the rearmost vertebrae
have been fused into a solid rod called the urostyle.
 Together the pelvis and urostyle make the bottom half of
the body very stiff.
 A flexible pectoral girdle and strong forelimbs provide
cushioning on landing.
http://www.k-state.edu/organismic/images/frog_skeleton.jpg
Order Anura

Anurans have inflexible bodies and unlike
salamanders, which swim in the same manner
as fish, they swim using simultaneous thrusts of
the hind legs.

There is dispute about whether the anuran body
form evolved because its mode of swimming is
more effective or because the large hind limbs
allowed anurans to occupy the boundary
between land and water and escape into either if
threatened.
Order Anura
 Anurans
differ in the relative dimensions of
their limbs and these differences relate to
their ecological specializations.
 Most
anurans given the common name
frog are long legged and move by
jumping. Shorter-legged terrestrial
anurans are usually called toads and they
move by making short hops.
Order Anura

Toads move around a lot looking for prey. This
makes them conspicuous, but being short
legged they cannot flee predators easily. Most
instead rely on defensive chemicals produced by
their skin for protection.

Frogs with their long legs are usually sit-andwait predators and flee predators by leaping
away. Most of them are not protected by toxins.
Leaping Frog
http://www.funfacts.com.au/
images/leaping-frog1.JPG
Woodhouse Toad
http://geoinfo.nmt.edu/staff/wilks/interests/
toads/images/Woodhouse%
27s-Toad-01.jpg
Arboreal frogs

There are many species of frogs specialized for
climbing in trees and shrubs.

These are usually slim and long legged with
large heads and eyes.

Some of the most specialized arboreal species
are called tree frogs and possess specially
modified toe pads that allow them to adhere to
surfaces.
Common Tree Frog
http://www.naturephoto-cz.com/photos/others/common-tree-frog-9282.jpg
Tree frog toe pads

The toe pads of tree frogs have an epidermal
layer made up of many projecting papillae
separated by small gaps.

Mucus glands secrete a viscous fluid that forms
a thin layer between the pad and the surface
being gripped and a combination of surface
tension and viscosity holds the frog in place.

These pads allow the frogs to adhere to vertical
and even beyond vertical surfaces.
White-lipped Tree frog: note toe pads
http://dic.academic.ru/pictures/enwiki/87/White_lipped_tree_frog_cairns_jan_8_2006.jpg
http://greenerloudoun.files.wordpress.com/2009/01/
frog20hanging20on20for20dear20life.jpg
Order Gymnophiona (Apoda)
 The
caecilians of which there are about
150 species have evolved a legless state
and are specialized for burrowing.
 They
look superficially like earthworms.
 Caecilians
are distributed worldwide and
most are tropical forest species that
burrow in moist forest soil.
Order Gymnophiona (Apoda)
 The
eyes have been greatly reduced in
size (fossil forms had much larger eyes)
and most species are blind as adults with
the eyes being covered by a layer of skin
(and in some cases bone).
Yellow-striped Caecilian
http://www.ecologyasia.com/images-a-j/caecilian-head_0007.jpg
Order Gymnophiona (Apoda)

The superficial resemblance to earthworms is
due in part to the regular skin folds (annuli) that
encircle the body.

The main annuli overlie vertebrae and myotomal
septa and reflect the underlying segmentation of
the body.

Many caecilians have dermal scales in pockets
of the annuli, so caecilians are the only living
amphibians with scales.
Caecilian: note prominent annuli.
http://static.howstuffworks.com/gif/caecilian2.jpg
Order Gymnophiona (Apoda)

Caecilians feed on worms and other
invertebrates that they find burrowing
underground.

They are probably helped to find their food by
another unique feature of the group, protrusible
tentacles, which are located either side of the
snout between the eye and nostril.

The tentacles probably transport chemicals to
the vomeronasal organ on the roof of the mouth.
Disappearing Amphibians
 In
the early 1990’s it became apparent that
amphibian populations worldwide were in
rapid decline.
 Subsequent
review suggested that at least
9 and perhaps as many as 122 species
had become extinct since 1980 and that
population declines were ongoing.
Disappearing Amphibians
 Localized
causes of declines that have
been identified include:



microclimate changes due to logging, which
results in less forest humid environments that
suit amphibians.
mining which often employs toxic chemicals
that amphibians are especially sensitive to.
Habitat destruction by cattle around breeding
ponds: young anurans e.g. become trapped in
hoofprints
Disappearing Amphibians
 On
a global level however there are a
number of factors that appear to be
associated with amphibian declines.
These include




Global warming
Acid rain
UV radiation
Disease
Global warming

Amphibian populations at high altitudes are declining
faster than those elsewhere.

As temperatures rise amphibians adapted to cooler
environments are pushed higher and higher up
mountains until they run out of habitat.

Studies in Queensland, Australia indicate that a 1ºC
increase in average temperature will diminish the core
available habitat for high altitude species by 65%. An
increase of 3.5ºC would eliminate the habitat of half of
these species.
Acid rain

In the Northern Hemisphere acid precipitation as
a result of industrial pollution has affected the pH
of water amphibians breed in.

Embryos of many species are killed at pH 5 or
below.

Sub-lethal effects also occur. For example,
spotted salamanders reared in acidic water are
less coordinated and grow more slowly because
they are less effective at catching prey.
UV radiation

Thinning of the ozone layer has resulted in higher levels
of UV rays reaching the Earth’s surface.

There is debate about how important the effects of UV
radiation are but UV-B radiation does kill amphibian eggs
and embryos.

For example only 50-60% of the eggs of Cascade frogs
in Oregon exposed to ambient sunlight hatched, but 7085% of those protected by a UV-B filter hatched.
UV radiation
 Factors
such as water turbidity and
variation in different species of amphibians
in their sensitivity to UV damage as well as
variation in the ability of different species
to repair UV damage complicate an
analysis of UV effects.
 As a result, certain species and breeding
sites appear to be unaffected by UV
radiation effects.
Disease

Most recently there has been increased focus on
the role of disease in amphibian declines.

In particular, attention has focused on
iridoviruses and chytrid fungi.

Iridoviruses infect a variety of salamanders, but
there appears to be a long evolutionary
relationship between hosts and pathogens and it
now appears that the viruses may cause local
population fluctuations but not extinctions.
Disease
 There
is much more concern about the
danger of chytrid fungi.
 This
fungus has been identified as
responsible for the disappearance of
amphibian populations from the Americas
to Australia and New Zealand.
Disease
 The
fungus in the form of motile zoospores
in water penetrates the skin and causes a
disease called chytridiomycosis.
 The
fungus forms a reproductive body
called a zoosporangium and this
interferes with respiration and control of
water flow and kills adult frogs.
Disease

Infected tadpoles appear to survive, but grow
slower than uninfected individuals.

The fungus appears to have originated in African
clawed frogs, which are resistant to it.

African clawed frogs have been used extensively
worldwide in lab work and many escaped or
were released into the wild bringing the fungus
with them.
Disease

Waves of chytridiomycosis infection have spread
along mountain chains in Central America,
South America and Australia and the effects on
local populations are often devastating.

It is likely that vulnerability to fungal infections is
increased because of the effects of stress on
immune systems. Thus, pollution, UV radiation
and acid rain may be making amphibians more
susceptible than they would otherwise be.