AmphibiansCh. 11.3

What is an Amphibian?

• An Amphibian is a vertebrate that is ectothermic and spends its early life in water.

• The word Amphibian means “double life.”

• After beginning their lives in water, most amphibians spend their adulthood on land, returning to water to reproduce.

Groups of Amphibians

• There are two major groups of Amphibians:– Salamanders (keep tails as adults)– Frogs/Toads (No tails as adults)

Reproduction and Development

• Amphibians have a life cycle that suits the “double lives” they lead.

• Eggs fertilized internally in most salamanders and externally in most frogs/toads.

• Fertilized eggs develop in water.• A few days later, larvae wriggle out of a

jelly that coats the eggs and begin swimming like fish.

• The larvae of most amphibians grow and eventually undergo metamorphosis.

• The larvae of a frog/toad is a tadpole.

• The larvae of salamanders look like tiny salamander adults.

• Salamanders go under metamorphosis and lost their gills.

Living on Land

• The respiratory and circulatory systems of adult amphibians are adapted for life on land.

• Adult amphibians have adaptations for obtaining food and moving.

Obtaining O2

• Amphibian larvae use gills to obtain O2.• During metamorphosis, most amphibians lose

their gills and develop lungs.• Lungs are organs of air-breathing vertebrates in

which oxygen gas and carbon dioxide gas are exchanged.

• Oxygen and carbon dioxide are also exchanged through the thin, moist skins of adult amphibians. THEY CAN BREATHE WITH THEIR SKIN!

Circulatory System

• A tadpole’s circulatory system has a single loop (like the fish) and a heart with 2 chambers (like the fish).

• When they become adults, they have 2 loops (like humans) and 3 chambers in their heart!

• Remember Atrium: on top

• Ventricle: on bottom (alpha order)

Why we draw hearts like:

• People were not allowed to dissect humans “back in the day” because of religious reasons. So all experiments were done on other animals and amphibians were easy to catch and didn’t cost a lot to dissect. In fact, frog dissection is still very popular.

• While dissecting frogs, they saw the shape of its heart. We just assumed our heart was the same. Now we know different, but we still like to draw our hearts the same as before.

Obtaining Food• Although most tadpoles are herbivores,

most adults are carnivores.

• Frogs and toads usually wait for their prey to come close. But salamanders actively stalk and ambush their prey.

• Frogs and toads have camouflage – they are usually brownish-green.

Movement

• A vertebrate that lives on land needs a strong skeleton to support its body against gravity.

• They also need a way to move.• Fins work on water, but not on land.• Salamanders usually crawl, but frogs and

toads can leap.• Leaping requires powerful hind-leg

muscles.

Amphibians in Danger

• Worldwide, amphibian populations are Worldwide, amphibian populations are de creasing. de creasing.

• One reason: Habitat destruction. One reason: Habitat destruction. People are destroying their habitat to People are destroying their habitat to cut down trees, make farms, sell the cut down trees, make farms, sell the wood to other countries, etc.wood to other countries, etc.

• When a swamp is filled in or a forest is When a swamp is filled in or a forest is cut, an area that was moist becomes cut, an area that was moist becomes drier.drier.

• Few amphibians can survive for long in dry, sunny areas.

• Amphibians are declining even in areas where the habitats are still intact.

• Because their skins are delicate and their eggs lack shells (they are like jelly-very squishy and soft), they are sensitive to the environment.

• Poisons in the environment, such as pesticides and other chemicals, can pollute the waters that amphibians need to live and reproduce.

• Even small amounts of these chemicals can weaken adults and kill eggs or cause deformed tadpoles.