Modern Amphibians

• Part two

Modern Amphibians: Order Caudata • Includes salamanders (may also be called newts).

• Members may be fully aquatic, fully terrestrial, or amphibious.

• Many reproduce in water. Some reproduce on land, with no swimming larval stage.

Modern Amphibians: Order Caudata • Larvae and adults are carnivorous.

• Some have no lungs, and respire through their skin only.

Modern Amphibians: Order Gymnophiona • Includes caecilians (legless amphibians that resemble small snakes).

• Most are burrowing. They have small eyes beneath skin or bone, and are often blind.

Modern Amphibians: Order Gymnophiona • All are carnivorous.

• All are thought to have internal fertilization.

• Some lay eggs which the female guards, others develop inside the female.

Phylogenetic Diagram of Amphibians

Characteristics of Amphibians: Skin Amphibian skin serves two important functions: • Respiration - The skin is permeable to gases and water. Mucous glands secrete a lubricant that keeps the skin moist in air.

• Protection - The skin protects amphibians from infection and secretes a foul-tasting or poisonous mucus that protects amphibians from predators.

Characteristics of Amphibians: Skeleton A strong skeleton supports the body of amphibians against the force of gravity.

• Vertebrae interlock to form a strong, rigid structure.

• Strong limbs assist with standing and walking.

• Pectoral and pelvic girdles transfer weight to the limbs.

• Skeletons of frogs are specialized for jumping and landing.

Characteristics of Amphibians: Skeleton • Fused bones add strength to the forelimbs and hind limbs.

• Thick arm bones and pectoral girdle absorb shock of landing.

• Long hind legs allow frogs to jump farther.

• Lengthened pelvic girdle and fused vertebrae add support.

Characteristics of Amphibians: Circulatory System

The circulatory system is divided into two loops.

•

Pulmonary circulation - carries deoxygenated blood from the heart to the lungs and back to the heart.

•

Systemic circulation - carries oxygenated blood from the heart to the body and back to the heart.

Amphibian Heart Structure

Amphibians use positive pressure breathing

Amphibian Lung Structure

Characteristics of Amphibians: Digestive System • Includes the pharynx, esophagus, stomach, liver, gallbladder, small intestine, large intestine, and cloaca.

• The upper part of the small intestine is called the duodenum.

• The coiled middle portion of the small intestine is the ileum.

Characteristics of Amphibians: Digestive System • A membrane that holds the small intestine in place is called the mesentery.

• Waste materials are stored in the cloaca and exit the body through the vent.

Characteristics of Amphibians: Digestive System Accessory Glands • The liver produces bile, which is stored in the gallbladder and helps break down fat.

• The pancreas secretes enzymes that help break down food into particles that can be absorbed by the blood.

Internal Structure of a Frog

Characteristics of Amphibians: Excretory System • The kidneys are the primary excretory organ, and filter nitrogenous wastes from the blood.

• Wastes combined with water are known as urine.

• Urine flows from the kidneys to the cloaca and then to the urinary bladder, which branches off the cloaca.

Characteristics of Amphibians: Excretory System • Nitrogenous wastes are converted from ammonia to urea, which is highly concentrated and helps conserve water.

Characteristics of Amphibians: Nervous System • The olfactory lobes are larger in amphibians than in fish.

• The cerebrum is responsible for behavior and learning.

• The optic lobes process information from the eyes.

• The cerebellum is responsible for muscular coordination.

• The medulla oblongata controls heart rate and respiration rate.

Characteristics of Amphibians: Nervous System

Sense Organs

• Larvae have a lateral line, most adults do not.

• The eyes are covered by a nictitating membrane, a transparent moveable membrane that protects the eye.

Characteristics of Amphibians: Nervous System

Sense Organs

• Sound is detected by the inner ear. • Sounds are transmitted to the inner ear by the tympanic membrane, or eardrum, and the columella, a small bone that extends between the tympanic membrane and the inner ear.

Reproduction in Amphibians: Courtship and Fertilization • Males attract females with a mating call.

• Females only respond to males of the same species.

Reproduction in Amphibians: Courtship and Fertilization • The male clings to the female in an embrace called amplexus.

• Eggs and sperm are released into the water.

• Fertilization is external.

Reproduction in Amphibians: Courtship and Fertilization • Male - includes two bean-shaped testes located near the kidneys that produce sperm during the breeding season.

Reproduction in Amphibians: Courtship and Fertilization • Female - includes a pair of large ovaries containing thousands of tiny immature eggs. During the breeding season the eggs mature.

Reproduction in Amphibians: Life Cycle • When the eggs hatch, a tadpole is released.

• The tadpole grows and slowly changes from an aquatic larva into an adult in a process called metamorphosis.

• Metamorphosis is controlled by a hormone called thyroxine.

Reproduction in Amphibians: Life Cycle • Some amphibians do not produce thyroxine and remain in the larval stage their entire life.

• Some amphibians do not have a larval stage and hatch from the egg as small versions of the adult.

Life Cycle of Frog

Reproduction in Amphibians: Parental Care

Parental care increases the likelihood that the offspring will survive.

•

Some species guard their eggs until they hatch.

•

Some species sit on their eggs to prevent them from drying out.

•

The male Darwin’s frog carries the eggs in his vocal sacs until the larvae finish metamorphosis.

•

Female gastric brooding frogs swallow their eggs and the larvae mature in the stomach.