Biology 10: Topic 12b: Class Amphibia (Kétéltűek)

- includes frogs, toads, newts, salamanders

- appeared about 350 million years ago: the environment at that time included periods of floods and droughts, there were lots of insects on land (in the air), there was more oxygen in the air than there had ever been before and there were LOTS of carnivorous fish in the seas!

- problems of moving out of water included the harsher climate that would cause the animal to dry out, the greater temperature changes that occur in air compared to water and the fact that on land there is no buoyancy, so the animals require a more supportive skeleton

Body Structure

1. head, trunk and 4 legs (or sometimes none). Toes have no claws and are often webbed

2. respiration: primitive internal lungs, but no muscles to coordinate breathing, so the animals “swallow” air. They also breathe through their skin. The skin is thin, lacks scales and contains glands that secrete mucus to keep it moist (gas exchange can only occur if it is moist). Some also have glands that excrete toxins (for protection)

3. circulation: three-chambered heart. There is some mixing of oxygenated and deoxygenated blood in the ventricle. Amphibians have double-circuit circulation, so there is a loop through the lungs and to the skin (pulmocutaneous circuit) and a loop through the body (systemic circuit)

Amphibian circulation

4. nutrition: predators, but most specialize as predators of insects, so we call them insectivores

5. reproduction: most species require water to reproduce. The eggs lack shells or thick protective membranes, so they must be kept in water to stay moist. Fertilization is external and occurs after courting (mating behaviours), which include things like the deep croaking in bullfrogs or in some species the male’s “thumb” enlarges in the reproductive period and he presses it into a point on the female’s back, which stimulates her to lay eggs. In general, amphibians do not care for their young.

6. metamorphosis is typical in amphibians:

o eggs hatch

o get a tadpole (ebihal), which has fins, a lateral line system, gills and a 2-chambered heart

o the tadpole feeds and grows and then goes through a period of transition where the fins, lateral line system and gills disappear and the 2-chambered heart develops into a 3-chambered heart

Amphibian life cycle

7. homeostasis: amphibians are ectotherms (poikilotherms), so their body temperature varies with the environmental temperatures, therefore, the majority of amphibians live in warm climates. Two dormant phases can be observed in amphibians, which they usually spend buried in mud: estivation if it is too hot, hibernation if it is too cold.

CLASSIFICATION – there are only 16 species in Hungary, ALL are protected

1. O. Urodela (farkos) – salamanders and newts

- some are totally aquatic (particularly newts), others live in damp places

- bend side to side when they move, because their leg joints are attached at the sides of the body and not under it

-internal fertilization is common in this group, there is no real tadpole stage. In some larval characteristics, like gills remain (called neoteny)

- in Hungary the fire salamander (foltos szalamandra) is found in beech (bükk) forests.

2. O. Anura (farkatlan) – frogs and toads

- legs are designed for jumping, eyes are found on top of head and covered with a retractable membrane (“pre-eyelid”), they have tympanic membranes behind the eyes with internal ears for sound and balance. They have vocal chords and males have large throat pouches to amplify the sound during mating.

- another unique feature of frogs are their long sticky tongues, fastened at the front of their mouths, designed for catching insects.

- warning colouration is common: highly colourful = highly poisonous

in Hungary, species include the edible frog (kecskebéka), the marsh frog (mocsári béka), the moor frog (gyepi béka) and the tree frog (leveli béka)

Edible frog

Marsh frog

Tree frog

- - toads are generally less agile, live in drier conditions and are more active at night. Their legs are shorter, their eggs are found in stringy masses and their tadpoles are typically black

in Hungary, species include the yellow-bellied toad (in the hills), the red-bellied toad (in the lowlands), the common toad (barna varangy) and the green toad.