Amphibians are a class of vertebrates that include frogs, toads,
salamanders, newts and caecilians. All amphibians are cold-blooded, and most lay
eggs. The majority of species undergo metamorphosis, moving from a larval stage
(usually aquatic) through the development of limbs and lungs to become
terrestrial adults. However, a significant minority of the species develop
directly from eggs, usually laid on land, without a larval stage. There are also
a few viviparous species that give birth to young, without laying eggs. Almost
all species are dependent on moist conditions, and many require freshwater
habitats in which to breed. The greatest diversity occurs in tropical forests,
with species richness generally lower in temperate and arid regions. Amphibians
are entirely absent from marine environments.
species are dependent on moist conditions, and many require freshwater habitats
in which to breed. The greatest diversity occurs in tropical forests, with
species richness generally lower in temperate and arid regions. Amphibians are
entirely absent from marine environments.
excellent indicators of the quality of the overall environment, as they are very
sensitive to perturbations in ecosystems.
have been around for an estimated 350 million years. The earliest known frog
appeared about 190 million years ago, during what is known as the late Jurassic
Genera: there are at least 303 known frog and toad genera
Species: there are about 4,000 known frog and toad species
Length: largest - Goliath frog Conraua goliath is 13.5 inches (30
centimeters); smallest - gold frog Psllophryne didactyla is 0.39 inches (1
Weight: up to 6.6 pounds (3 kilograms) for Goliath frog
Life span: 1 to 30 years
Number of eggs laid: from 2 to more than 50,000, depending on the
Incubation: 14 to 23 days
Age of maturity: 2 months to 1 year
almost everywhere on Earth except Antarctica, the Arctic, and
Habitat: nearly every kind of habitat except polar regions and very
Toads and frogs are
amphibians, and the word "amphibian" comes from Greek words meaning
"double life." This refers to the fact that during a frog's life, it
lives both in the water and on land -- one of the reasons we find amphibians so
fascinating. The amazing change, or "metamorphosis" -- that happens in
a frog's life follows this pattern:
spring, male frogs and toads move to watery breeding sites and start calling
to attract females and, in some cases, to warn other males to keep away from
male and female pair up, the male clasps the female in a piggyback position
called amplexus, releasing his sperm as she releases her eggs. The eggs are
fertilized outside the female's body.
of soft, jelly-coated eggs, often numbering in the hundreds or thousands,
often sticks to water plants or other vegetation. The eggs hatch into tiny
fish-like tadpoles that have gills, like fish, to allow them to breathe
while in the water.
usually grows quickly, swimming around and eating algae or tiny organisms in
sprout from the tadpole's body, and the tadpole's tail becomes smaller,
actually being absorbed into the body. The tadpole also develops lungs to
allow it to breathe out of water. Its intestines change from a long coiled
gut to a short gut, to accommodate the change in diet from a grazing tadpole
to a meat-eating frog. It is thought during metamorphosis that the immune
system is largely shut down to accommodate all the physical changes.
Tadpoles are especially susceptible to disease and parasite attacks at this
tadpoles are eaten by fish, birds or other frogs -- but the ones that
survive these early stages continue their transformation into adult frogs
that can move out of the water and live on land.
spring, adult frogs move into the water again to mate and the cycle starts
all over again.
are cold-blooded (or poikilothermic) vertebrate animals. They differ from
reptiles in that they lack scales and generally return to water to breed. They
are one of three types of Amphibians. Anura, also called Salientia, (frogs and
toads), caudate (salamanders and newts) and caecilians (worm-like amphibians).
Frogs and toads are carnivores -- that is, they eat other animals, typically
bugs and worms. Frogs are beneficial to humans because they eat so many insect
Frog and a Fawn Deer
goliath is the world's largest frog; its body can be more than a foot long, and
its entire length, back legs extended, is often more than two and a half feet.
They have been known to weigh more than seven pounds.
Class Amphibia - frogs and toads, newts
and salamanders, and caecilians - first appeared on Earth during the Devonian
Period (360 to 408 million years ago). While many amphibian species have evolved
and gone extinct over the millenia, more than 5000 species exist today. Various
amphibians have adapted over this expanse of time to occupy different habitats,
including wetlands, forests, deserts, prairies, and savannas. By the time human
civilizations were established, amphibians were present in all but the most
inhospitable of regions. Until recently, whether you lived in a city, a suburb,
or a rural area anywhere in the world, chances are you weren't too far away from
a frog, toad, salamander, or caecilian.
So what has changed? In short, the number
of amphibians out there.
Amphibian populations are in decline in
many areas of the world. In cities and the countryside, in rainforests and
wetlands, countless areas which previously hosted a range of healthy amphibian
populations now have fewer - and even no - frogs, toads, and salamanders. While
healthy populations of some species may exist elsewhere in some cases of
declines, a few species - including Costa Rica's Monteverde golden toad and
Australia's Gastric brooding frog - are now believed extinct.
What's causing these mysterious declines?
Scientists conducting field research have produced compelling evidence for
habitat loss, climate change, UV radiation, contaminants and pollutants,
disease, and predation by invasive species as possible causes. Even more
baffling, amphibian declines are not necessarily occurring in "likely"
places where human impacts are obvious, such as cities and suburbs prone to
development and pollution; indeed, some of the most noted and dramatic declines
are happening in "protected" areas such as national parks.
The scientific community now suspects that
there is no one reason for worldwide declines of amphibians. For example,
diseases or pollutants that have decimated a species in one part of the world
may be completely absent in another region that has also experienced a
mysterious die-off of its amphibians. In some cases, die-offs can be attributed
to a specific cause; in others, the cause is not so obvious. Many researchers
believe that multiple, additive causes - for instance, a high incidence of UV
radiation combined with the presence of a disease - may be at the heart of large
numbers of worldwide declines.
Chytrid Fungus (KIT-rid) (Batrachochytrium
sp.) is an epizootic and a major contributor to the decline of amphibian
populations around the world, threatening many species with extinction.
This fungus is a global emerging amphibian
pathogen which is proving to be one of the worst vertebrate infectious diseases
found so far. It is causing a huge amount of extinction and disease within
amphibian populations. More than 100 species of amphibians are known to be
affected by the chytrid fungus (Batrachochytrium dendrobatidis). Some are very
susceptible and die quickly while others which are more resistant are carriers
of the pathogen.
The disease, called Chytridiomycosis, is
already credited with wiping out frogs and toads in large numbers in Australia
and South America.Why a particular type of this fungus has become pathogenic to
amphibians is not yet known.
Chytrid fungus invades the thin, permeable
skin of amphibians and appears to kill them by interrupting their ability to
regulate the movement of water and oxygen through their skin.
An Early Indicator of
Because they are
more vulnerable than many other creatures, amphibians are considered a ``canary
in the coal mine'' for environmental damage. The canary was used for detecting
toxic or explosive gases in coal-mines, before there was a better way to do it.
More sensitive to such gases than humans, they would collapse long before the
miners were affected, and a collapsed canary was therefore a signal to the
miners to get out immediately, and to management to look at the problem and
clean up the mine
of Malformation Reports
The continental United States is home to at
least 230 amphibian species: 90 frog and toad species, and 140 species of
In the U.S., declines are particularly
serious in California, the Rocky Mountains, the Southwest, and Puerto Rico.
Worldwide, decline "hot spots" also include Australia and Central
deformities - extra limbs, malformed or missing limbs, and facial
malformations - have been documented in 44 states, and involve nearly 60
species. In some local populations, up to 60% of the amphibians exhibit
confirmed factors causing amphibian declines and malformations
alteration and Fragmentation
Roads, introduced species,
or other factors separate remaining populations of amphibians from each
Non-native species prey on
or compete with native amphibians
Amphibians are removed
form the wild and sold internationally as food, as pets, or for
medicinal and biological supply markets
Amphibians are extremely
sensitive to small changes in temperature and moister. Changes in global
weather patterns (e.g. El Nino events or global warming) can alter
breeding behavior, affect reproductive success, decrease immune
functions and increase their sensitivity to chemical contaminants.
Levels of UV-B radiation
in the atmosphere have risen significantly over the past few decades.
Researchers have found that UV-B radiation can kill amphibians directly,
cause sublethal effects such as slowed growth rates and immune
dysfunction and work synergistically with contaminants, pathogens and
Chemical stressors, such
as pesticides, heavy metals, acidification and nitrogen based
fertilizers, can have lethal, sublethal, direct and indirect on
amphibians. Some of these include death, decreased growth rates,
developmental and behavioral abnormalities, decreased reproductive
success, weakened immune systems and hermaphroditism.
A combination of new
diseases or more susceptible amphibians leads to deaths of adults and
There has been a recent
increase and widespread occurrence of deformities (or malformations) in
natural populations of amphibians and has recently been perceived as a
major environmental problem.
Multiple factors can act
together to cause mortality or sublethal effects.
around the world have showed increasing signs of stress in recent years.
Some species have disappeared, and others are no longer found where they
used to be. An increase in deformities may be a sign that something is
concerned about what's happening to the frogs, because the health of frogs
is closely linked to the health of the environment. Frogs are sensitive to
pollution, because they live at the meeting of two environments -- land and
water -- and they can easily absorb pollutants through their skin.
declining, as are most, if not all other groups of life on Earth. This loss
of biodiversity should be a cause of concern to all of us.
(scientists who study amphibians and reptiles) have reported finding frogs with
missing legs, extra legs, misshapen legs, paralyzed legs that stuck out from the
body at odd places, legs that were webbed together with extra skin, legs that
were fused to the body, and legs that split into two half-way down. They have
also found frogs with missing eyes. One one-eyed frog had a second eye growing
inside its throat.
Amphibians are good
"indicators" of significant environmental changes that may go
initially undetected by humans. Humans breathe through lungs, which are inside
our bodies and thus protected from direct contact with air and water.
Amphibians, however, breathe partially (and in some species, completely),
through their skin, which is constantly exposed to the environment. Their bodies
are much more vulnerable and sensitive to factors such as disease, pollution,
toxic chemicals, radiation, and habitat destruction. The worldwide occurrences
of amphibian declines and deformities could be an early warning to us of serious
current global loss of species is a process generated by the activities of
humans. As we modify our environment for our own ends, it is clear that the
destruction of the habitats of other species leads directly to their
disappearance. However, more recently we have begun to observe, and to speculate
about more subtle impacts that human activities may be having, acting at a
We have depleted
atmospheric ozone levels; pollutants are accumulating in the natural systems on
which we and other organisms depend; we may be altering weather patterns. Such
gradual, but fundamental changes are certain to have an effect on the ecosystem.
It is possible that amphibians are responding adversely to these changes. They
may be showing us how our activities are affecting our shared ecosystem.
world's frogs, toads and newts and other amphibians are dying out, with
populations falling each year, according to research.
One of the biggest studies of
its kind reveals that amphibian numbers have declined dramatically over the past
40 years. The findings were compiled using Internet contacts with some 200
scientists around the world. Pollution, intensive farming, disease and climate
change are all likely to have played a role said Jeff Houlahan, a PhD candidate
in biology from the University of Ottawa in Ontario, Canada who spearheaded the
report. Data on 936 populations of amphibians and 157 species came in from 37
countries and eight regions of the world.
data covering the last four decades, the analysis concluded the world's
amphibian population has likely decreased by more than 50 per cent since the
was steepest in the 1960s -- as much as 15 per cent a year -- but continued at a
slower rate, roughly two per cent, in the 1980s and '90s. North America has shown
the greatest fall in amphibian populations in recent years.
the Frog joined USGS scientists on Capitol Hill to call attention to amphibian
declines and deformities
Q: Why should we care
about these dramatic declines, deformities, and disappearances plaguing many
amphibian populations around the world?
A: Amphibians are good indicators
of significant environmental changes. Amphibians, unlike people, breathe at
least partly through their skin, which is constantly exposed to everything in
their environment. Consequently, their bodies are much more sensitive to
environmental factors such as disease, pollution, toxic chemicals, ultraviolet
radiation, and habitat destruction. The worldwide occurrences of amphibian
declines and deformities could be an early warning that some of our
ecosystems--even seemingly pristine ones--are seriously out of balance.
Q: What kinds of
malformations have been noticed, and how widespread is the problem?
A: Multiple limbs, missing limbs,
and facial abnormalities are the main developmental malformations seen.
Malformed amphibians are now documented in 44 states, in 38 species of frogs and
19 species of toads, with estimates of deformities as high as 60 percent in some
local populations. Scientists now agree that current numbers of reported
malformations significantly exceed the normal statistical variation.
Q: Where have amphibian
declines been noted?
A: Scientists have documented
four major "hot spots" for amphibian declines: western North America,
Central America, northeast Australia, and Puerto Rico. Researchers believe that
all of these declines--most in seemingly pristine areas--have occurred since
around 1980. Other areas of the world may also be affected by such declines, but
until research is conducted in other continents and regions, the extent of
possible declines is unknown.
In the United States and its
territories, major declines of frog populations have been noted in California,
in the Rocky Mountains, in Puerto Rico, and in areas of the Southwest. Some of
these declines have occurred in some of our Nation's largest parks and
wilderness areas, where we would expect wildlife to be most protected. Northern
leopard frogs, for example, have disappeared or become rare over much of their
known range in western North America. Boreal toads have undergone an 80 percent
decline in the southern Rocky Mountains. In parts of the Sierra Nevada and
adjacent foothills, several amphibian species--including mountain and foothill
yellow-legged frogs and red-legged frogs--have declined over areas of 100 square
miles or so. And in Puerto Rico, almost two-thirds of the native amphibians are
declining; some species have not been found for several years.
Q: Are there any
worldwide patterns of amphibian declines?
A: The worldwide pattern of
amphibian declines includes both loss of populations from parts of species'
ranges--the pattern seen in Australia and Central American tropics with stream
frogs--and declines of entire species, such as ranid frogs in California and the
Southwest, and the "poster frogs" for amphibian declines, the golden
toad in Costa Rica and an Australian frog that broods its young in its stomach.
Q: How many amphibian
species are there in the United States?
A: There are about 230 species of
amphibians, including about 140 species of salamanders and 90 species of frogs
and toads, that occur in the continental United States. Amphibians have two
major patterns of distribution: confined to one location--that is, endemic--or
widespread. Scientists estimate that the number of endemic species that have
suffered losses has increased from 33 species in 1980 to 52 species in 1994.
Q: What are the leading
causes of frog declines and deformities?
A: There does not appear to be
one "smoking gun"; numerous environmental factors are probably
responsible for the declines and deformities. Limited research findings and
anecdotal information suggest several possible causes, including habitat loss,
introduction of non-native predators such as fishes and bullfrogs, disease, and
possibly airborne contaminants. Scientists who have studied amphibian declines
and deformities agree that the deformities are unlikely to have caused the
extensive, well-documented declines of many amphibian species worldwide.
Deformities in different localities probably have different causes. Recent USGS
research indicates that some malformations may have both site-specific and
Countries with Highest
Percentage of Threatened Amphibians
guidelines intended to guard amphibians against deadly fungus-Click
Evolution in Losing Race With Environmental Change-Click
weed killer demasculinizes frogs, disrupts their sexual development-Click
radiation can cause physical deformities in amphibians-Click