2012 Update 40 Notes: Amphibians Table of Contents: Section 1 Origin and Evolution of Amphibians Section 2 Characteristics of Amphibians Section 3 Reproduction in Amphibians 40-1 Origin and Evolution of Amphibians Objectives: Describe the three preadaptations involved in the transition from aquatic to terrestrial life. Describe two similarities between amphibians and lobe-finned fishes. List five characteristics of living amphibians. Name the three orders of living amphibians, and give an example of each. Why so brightly colored, Frog-boy? 1:00 Adaptation to Land Preadaptations - are adaptations in an ancestral group that allow a shift to new functions which are later favored by natural selection. Lobe-finned fishes had several preadaptations that allowed them to transition to life on land: · bone structure · pouches in digestive tracts for gas exchange · nostrils · higher metabolism · efficient hearts ICHTHYOSTEGA 2012 Update Ichthyostega Characteristics Adaptation to Land, continued Characteristics of Early Amphibians Amphibians and lobe-finned fishes share many anatomical similarities, including: · similar skull · similar vertebral column · similar bone structure in fins and limbs · early amphibians had a large tail fin and lateral line canals Crossopterygian 2012 Update Adaptation to Land, continued Diversification of Amphibians About 300 million years ago amphibians split into two main evolutionary lines. One line included ancestors of reptiles, the other line included the ancestors of modern amphibians. Adaptation to Land, continued Diversification of Amphibians Today there are about 4,500 species of amphibians belonging to three orders: · Anura - includes frogs and toads · Caudata - includes salamanders and newts · Gymnophiona - includes caecilians (legless tropical amphibians) Modern Amphibians Modern amphibians share several key characteristics Most change from an aquatic larval stage to a terrestrial adult form, in a transformation called metamorphosis. Most have moist, thin skin withno scales. Feet, if present, lack claws and often are webbed. Most use gills, lungs, and skin in respiration. Eggs lack multicellular membranes or shells, are usually laid in water, and are usually fertilized externally. Characteristics of Modern Amphibians Types of Amphibians 2012 Update Modern Amphibians, continued Order Anura Order includes frogs and toads. Members may be fully aquatic, fully terrestrial, or amphibious. Most reproduce in water, laying eggs that hatch into swimming larvae called tadpoles. Larvae are herbivores. Adults are carnivorous and will eat any animal they can capture. Chorus Frog Modern Amphibians, continued 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. Larvae and adults are carnivorous. Some have no lungs, and respire through their skin only. Tiger Salamander Modern Amphibians, continued 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. All are carnivorous. All are thought to have internal fertilization. Some lay eggs which the female guards, others develop inside the female. 2012 Update 40-2 Characteristics of Amphibians Objectives: Relate the structure of amphibian skin to the types of habitats in which amphibians can survive. Identify three adaptations for life on land shown by the skeleton of a frog. Sequence the flow of blood through an amphibian’s heart. Describe how a frog fills its lungs with air. Describe the digestive and excretory systems of amphibians. Discuss an amphibian’s nervous system. 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. 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. 2012 Update Skeleton, continued 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. 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. 2012 Update V 2.0 fish V 3.0 heart Respiration Amphibians use two forms of respiration Pulmonary respiration - respiration through the lungs Cutaneous respiration - respiration through the skin 2012 Update Respiration, continued 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. 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. Digestive System, continued 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. 2012 Update Internal Structure of a Frog 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. Nitrogenous wastes are converted from ammonia to urea, which is highly concentrated and helps conserve water. 2012 Update 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. 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. 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. 40-3 Reproduction in Amphibians Objectives Explain how a male frog attracts a female of the same species. Discuss the reproductive system of a frog. Describe the life cycle of a frog. Describe the changes that occur during metamorphosis in frogs. Identify two examples of parental care in amphibians. 2012 Update Courtship and Fertilization Males attract females with a mating call. Females only respond to males of the same species. The male clings to the female in an embrace called amplexus. Eggs and sperm are released into the water. Fertilization is external. Courtship and Fertilization, continued Reproductive system Male - includes two bean-shaped testes located near the kidneys that produce sperm during the breeding season. Female - includes a pair of large ovaries containing thousands of tiny immature eggs. During the breeding season the eggs mature. 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. 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. 2012 Update 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..