Frogs and Toads that Live in the Desert
From the article: Frogs and Toads in Deserts by Lon
McClanahan, Rodolfo Ruibal and Vaughan Shoemaker
Vocabulary: physiology, anurans, caecilians, metamorphosis,
stratum corneum, permeable, adaptation, clumping,
SLIDE 1
+Amphibians seem unlikely creatures to live in the desert, but
those living in dry climates show some unusual adaptations to live
in such extreme environments.
+Scientists have begun to examine the physiology of these animals
to better understand how they survive.
++You should remember that physiology refers to how organisms
function or how things work in animals.
+With their moist skin and aquatic lifestyle, frogs and toads seem
better suited to life near bodies of water.
+Yet these creatures are found in arid regions throughout the world
from the Sonoran Desert in the Southwest US to African savannas.
+ To survive in such climates, these animals have developed
behavioral and physiological mechanisms that allow them to
conserve water and remain cool.
+Scientists have changed the way they think about how anurans
(a-nor-uns) live in arid environments.
++Get this in your notes: anuran is any tailless stout-bodied
amphibians with long hind limbs for leaping and includes frogs
and toads.
+The study of desert-dwelling amphibians has offered insights into
the diversity of these animals.
SLIDE 2
++You should know that:
Amphibians were the first vertebrates to move out of the water on
to land 300 million years ago, yet most of them still need to remain
close to sources of fresh water.
++There are three types of modern amphibians:
1. salamanders
2. anourans (a –nor-uns)
3 caecilians (see-sill-ee-ons)
+Caecilians are a legless, wormlike amphibians that live
underground – they are not worms and they are not snakes,
+ snakes have scales and a tail – see-cill-ee-ons do not.
+ See-cill-eee-ons have a skull and backbone – but worms do not.
SLIDE 3
+Getting back to a-nor-uns …
++Scientists use two characteristics to divide the order of a-noruns:
1. those with warty skin are called toads
2. those with smooth skin that live in and around water are called
frogs
+Most amphibians lay their eggs in water and have larvae that lead
a fish-like existence in water until they undergo metamorphosis.
+Once equipped with legs and lungs, they spend at least part of
their life on land.
+Metamorphosis – means a profound change in body form from
one stage to the next in the life of an animal
+Most amphibians live near fresh water or areas of high humidity
and rainfall.
+However, a few anourans (a –nor-uns) live in arid regions,
making it difficult to survive.
+You see -animals that live in arid regions usually have skin to
protect them from drying out.
+Reptiles, birds, and mammals have an outer layer of skin or shell
that protects them.
SLIDE 4
+The outer part or skin is called the stratum corneum – which is
composed of several layers of dead cells –
+this layer prevents water loss.
+Amphibians on the other hand, only have one layer.
+Their skin is permeable – permeable means to allow things to
travel back and forth through it.
++There are 2 advantages of permeable skin:
1. animals like frogs with permeable skin can absorb water through
their skin, rather than have to drink water
2. Oxygen and carbon dioxide can also pass through the skin - for
example, lungless salamanders (salamanders that lack lungs)
breathe entirely through their skin
+Frogs and toads use other adaptations to survive in deserts and
dry environments.
+An adaptation is adjusting or changing the way an animal
survives to fit the environment in which they live
SLIDE 5
++Frogs and Toads use 5 adaptations to survive:
1. they stay near what little water is available –
2. they clump together in large groups
3. they store waste in their body
4. they burry themselves underground
5. they cover themselves with waxes or other substances
+Perhaps the best adaptation is to stay near what little water is
available.
+So frogs and toads stay near wet seeps and springs.
+The California tree frog found in deserts does just that….it seeks
and searches out small seeps and spots of water during dry times.
+This frog also clumps with other California tree frogs in large
groups during the hottest time of the day.
+Scientists think the “clumping” decreases the amount of water
lost by any one individual frog.
+Another way to conserve water is through waste products.
+Frogs and toads differ from birds and reptiles in the way they
excrete wastes.
+Birds and reptiles excrete waste as a solid form and
+little water is lost or they conserve water by creating urine that
has a high concentration waste.
+In frogs and toads, when water is not available, these animals can
stop producing urine
+ or store waste as diluted urine.
+When frogs and toads lose water through evaporation, water from
the urine is recycled back into the body.
SLIDE 6
+Another way to conserve water is for a frog or toad to burrow or
bury itself underground.
+Frogs and toads that burrow can keep cool from the cooler
ground temperatures and they can also absorb water from moisture
in the soil.
+Some frogs and toads do this on a short-term basis, whereas other
can burrow themselves in soil
+and survive for up to two years without water.
+For frogs and toads that burrow underground, they can remain
there for some time,
+and falling rain drops will often bring them out of their burrow so
they can replenish their water in their bodies.
+ Scientists have found that getting the soil wet was not enough to
get the desert spade foot toad out of its burrow.
SLIDE 7
++This is important to know, burrowing toads, like the spadefoot
toad, uses the “sound” of rain falling to trigger it to come out of its
burrow.
+Scientists that by just getting the ground wet with water was not
enough to get the toad to emerge,
+yet when they placed a piece of plastic on the ground above a
burrow and sprinkled water on it, the toads emerged.
+As the spadefoot toads emerged from their burrows, they found
that the “sound of rain” was what triggered them to come out.
+Once out, they headed for water and usually stayed there for
about 24 hours, just long enough to mate and lay eggs.
+They then left and sometimes traveled back to their borrows.
+ Still another toad called the Budgett's Frog of Paraguay lives in
temporary ponds.
SLIDE 8
++In times of drought, it makes 2 critical adaptations to survive:
1. When the pond dries up, it burrows under the dried pond.
2. Once in the dirt, it forms a cocoon around its body to further
prevent water loss.
+So the last adaption is that frogs or toads cover themselves with
either a cocoon or other substances.
+For Budget’s frog, the cocoon prevents water loss.
+While most frogs shed the outer layer of skin, Budgett’s frog
keeps the outer layer of skin and continues to form additional
layers every 24 hours until the cocoon is fully formed.
+Once the cocoon gets wet, the frog will use its hind legs to roll up
the cocoon from the rear of its body
+and then it eats it.
SLIDE 9
+Another frog, The Waxy Monkey frog lives high in trees in dry
environments.
+This tree frog excretes a waxy substance from glands in its skin
+and covers its body to prevent water loss from evaporation.
+It uses each foot to wipe its entire body with a waxy substance.
+ Once covered, any water that falls from rain beads up and rolls
off its body.
+In fact, this frog drinks water as it rolls off its body.
+This is the only frog that is known to drink water.
+As you have seen, frogs and toads use multiple adaptation to
survive.
+However, in the few decades, populations of frogs and toads has
been on the decline and, in some cases went extinct.
+Their loss has been mostly because of habitat destruction by
humans.
+To prevent further declines, scientists need to better understand
the physiology of frogs and toads to save these anurans.
Reference:
McClanahan, L., Ruibal, R., & Shoemaker, H. (March 1994). Frogs and
toads in deserts. Scientific American, 270, 82-88.