Amphibian Adaptations and Physiology

• Most amphibians begin life as aquatic organisms and then live on land as adults

Adaptations for the move to land

• Tetrapods are four-legged vertebrates that first appeared on Earth 360 million years ago
• Key challenges included gravity, air buoyancy, temperature variations, and sound detection in air
• Limbs develop and skeletal/muscular systems become stronger
• Lungs enable animals to get oxygen from air more efficiently
• Development of behaviors, such as migration, and physical adaptations that protect them from extreme temperatures
• Animals evolve ears that detect sound waves in the air

Amphibian Characteristics

• Undergo metamorphosis to live on land
• Begin as limbless, gill-breathing tadpoles
• Tadpoles undergo daily metamorphosis, developing hind legs, forelimbs, and shortening tails
• Lungs replace gills
• Possess four legs, moist skin without scales, a double-loop circulatory system, and aquatic larvae
• Exchange gases through both skin and lungs

Feeding and Digestion

• Frog larvae typically are herbivores, while salamander larvae are carnivores
• Adults from both groups become predators
• Adults feed on invertebrates and small vertebrates
• Salamanders and legless amphibians catch prey in their jaws
• Food moves through the esophagus to the stomach for initial digestion
• Enzymes from the pancreas aid digestion in the small intestine
• Nutrients absorb into the bloodstream from the small intestine
• Waste moves to the large intestine before elimination
• Intestines end in the cloaca, where wastes and reproductive cells exit

Waste Removal and Gas Exchange

• Kidneys filter wastes from the blood
• Amphibians in water excrete ammonia, while those on land excrete urea
• Urea is made from ammonia in the liver and stored in the urinary bladder before exiting through the cloaca
• Larvae exchange gases through skin and gills
• Adults breathe through lungs, thin/moist skin, and mouth cavities

Circulation and Sensory Adaptations

• Amphibians have a double-loop circulatory system
• Oxygen-poor blood moves to the lungs and skin, while oxygen-filled blood returns to the heart
• Oxygen-filled blood then circulates from the heart to the body
• The amphibian heart consists of three chambers
• The right atrium receives the oxygen-poor blood from body
• The left atrium receives the oxygen-rich blood from the lungs
• The ventricle is undivided
• Sight is used to locate prey and evade predators
• Nictitating membranes, clear eyelids, protect the eyes
• The Tympanic membrane is an eardrum for hearing high-pitched sounds and amplifying vocal cords

Thermoregulation and Reproduction

• Amphibians are ectotherms, gaining body heat from the external environment
• Fertilization is primarily external
• Shell-less eggs must be laid and fertilized in water
• Tadpoles hatch and metamorphose from fishlike to air-breathing forms

Amphibian Diversity

• Modern amphibians are classified into three orders
• Anura (frogs and toads)
• Caudata (salamanders and newts)
• Gymnophiona (caecilians)

Frogs vs Toads

• Frogs have more powerful legs for jumping
• Frogs have moist, smooth skin
• Toads have bumpy, dry skin
• Toads generally live farther from water and possess glands that release a foul-tasting poison

Salamanders and Newts

• Salamanders and newts have long, slim bodies with necks and tails
• Most have four legs, thin/moist skin, and lay eggs in water
• Larvae look like small salamanders with gills
• Salamanders live near water in moist areas
• They feed on worms, frog eggs, and insects
• Newts are aquatic through life

Caecilians

• Caecilians lack legs, are wormlike, and burrow in soil
• They feed on worms
• Possess skin-covered eyes
• Utilize internal fertilization and lay eggs in moist soil near water
• Found primary in tropical forests

Vocabulary

• Cloaca
• Nictitating membrane
• Tympanic membrane
• Ectotherm
• Metamorphosis

Explore the key adaptations that enabled vertebrates to transition to land. This quiz covers gas exchange, circulation, digestion, and waste excretion in amphibians. Test your knowledge of amphibian biology with these questions.