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AMPHIBIAN NOTES. EXTERNAL STRUCTURE AND MOVEMENT. Amphibian skin does not have scales , feathers, or hair . It does have secretions that help with protection. These glands also keep skin moist to prevent drying. They also produce toxic chemicals that discourage potential predators.
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EXTERNAL STRUCTURE AND MOVEMENT • Amphibian skin does not have scales, feathers, or hair. • It does have secretions that help with protection. • These glands also keep skin moist to prevent drying. • They also produce toxic chemicals that discourage potential predators.
EXTERNAL STRUCTURE AND MOVEMENT • Chromatophores are specialized cells in the skin that are responsible for skin color and color changes. • Cryptic coloration, aposematic(warning) coloration, and mimicry are all common in amphibians.
Support and Movement • Animals that live in water are partially supported by water. • Animals that live on land have to support themselves against gravity. • Amphibian skulls are flattened, are relatively small, and have fewer bones than water-dwelling animals. • These changes keep the skull light so it can be supported out of water. • Amphibians also have changes in jaw structure and muscles to allow them to crush prey held in the mouth.
Support and Movement • The amphibian vertebral column is modified to provide support and flexibility on land. • Amphibians do have a neck. • They also have a sternum which supports the forelimbs and protects internal organs. • Amphibians have a pelvic girdle that has 3 bones. • These bones attach pelvic appendages to the vertebral column. • This is very important in providing support on land.
Support and Movement • Amphibians depend more on appendages than on the body wall for movement. • Therefore, muscles on the body wall are not as strong as muscles in their appendages.
Support and Movement • In the water, salamanders move like fish. • On land, they walk and it makes their body curve. • Caecilians move like an accordion, pushing and pulling at the same time. • Anurans have long hindlimbs that are modified for jumping. • They also have connective tissue and muscles in the forelimbs that act as shock absorbers.
Nutrition and the Digestive System • Most adult amphibians are carnivores and eat a wide variety of invertebrates. • Some anurans are more diverse. • The main factors that determine what amphibians will eat are prey size and availability. • Most larvae are herbivores and eat algae and other plant matter.
Nutrition and the Digestive System • Most amphibians locate their prey by sight and simply sit and wait for it to pass by. • Water amphibians depend more on their sense of smell. • Many salamanders use only their jaws to capture prey. • Some salamanders and most anurans use their tongue and jaw in a “flip-and-grab” method.
Nutrition and the Digestive System • Amphibians have the first true tongue. • Mucous and gland secretions make the tip of the tongue sticky. • When prey comes within range, the tongue comes out, the tip traps the prey, and then trapped in the mouth. • This whole process happens in about 0.5 seconds! • The tongue then pushes the food toward the esophagus, and the eyes sink downward to help force the food.
Circulation, Gas Exchange, Temperature Regulation • Gas exchange occurs across the skin in amphibians, as well as in the lungs. • So blood coming into the right side of the heart has almost as much oxygen as blood coming from the lungs.
Circulation, Gas Exchange, Temperature Regulation • In addition to a vascular system that circulates blood, amphibians also have a well-developed lymphatic system that helps return fluids and proteins to the blood vessels and also helps transport water across the skin.
Circulation, Gas Exchange, Temperature Regulation • Land animals expend much less energy exchanging gas than water animals do. • This is because air contains 20 times more oxygen than water. • There are 2 factors that permit amphibians to exchange gas across the skin: their skin is very moist, and their skin also has a rich supply of capillaries. • Gas exchange across the skin is called cutaneous respiration and can occur on land or in water. • This ability allows frogs to spend the winter in mud at the bottom of a pond.
Circulation, Gas Exchange, Temperature Regulation • In salamanders, gas exchange can also occur in the mouth and pharynx. • This is buccopharyngeal respiration. • Most amphibians have lungs. • Salamander lungs are very simple sacs. • Anurans have divided lungs, providing more surface area for gas exchange. • Amphibians larvae and some adults breathe using external gills.
Circulation, Gax Exchange, Temperature Regulation • Amphibians are ectothermic (they depend on external heat sources to maintain body temperature). • When in the water, they will take on the temperature of the water. • On land, their body temperature can be different from the environment. • Temperature regulation is mainly behavioral. • Many amphibians are nocturnal and remain in cooler burrows or under leaves during the hottest part of the day. • They may warm themselves by basking in the sun.
Nervous and Sensory Functions • The nervous system of amphibians is similar to that of other vertebrates. • Their brain has 3 sections: forebrain, midbrain, and hindbrain. • Amphibians have many sensory receptors on their skin. • They also have a lateral line system similar to fish and this helps aquatic amphibians.
Nervous and Sensory Functions • Chemoreception is an important sense for many amphibians. • Smell is used in mate recognition, detecting toxic chemicals, and in locating food. • Vision is one of the most important senses for amphibians because they are primarily sight feeders, often responding to the movements of their prey.
Nervous and Sensory Functions • Some amphibian eyes are on the front of the head and some are more to the side. • The lower eyelid is movable, and it cleans and protects the eye. • Much of it is transparent and is called the nictitating membrane.
Nervous and Sensory Functions • Amphibians auditory system is an adaptation for living on land. • It transmits both underground and airborne vibrations. • Anuran ears are made up of tympanic membrane, a middle ear, and an inner ear. • Anurans can screen out either high or low frequency sounds, depending on the situation. • Salamanders have no tympanic membrane or middle ear. • They have no mating calls, and the only sounds they hear are probably low-frequency vibrations.
Excretion and Water Regulaton • Amphibians do have kidneys. • Their waste product is either ammonia or urea, depending on where they live. • One of the biggest problems amphibians have is controlling the amount of water and salt in their body. • In water, they must get rid of excess water while keeping essential ions. • On land, they must conserve water.
Excretion and Water Regulation • They can not replace water in the usual ways. • So they limit water loss by using behavior that avoids exposure to conditions that cause water loss. • For example, many amphibians are nocturnal. • Those that are active day AND night can rehydrate by going back in the water. • Some amphibians have protective covering that reduce water loss. • Others may form cocoons that cover the body during dormancy. • They can also temporarily store water in the urinary bladder and lymph sacs.
Reproduction, Development, Metamorphosis • Amphibians have separate males and females. • Fertilization is usually external, and because the developing eggs do not have protective covering, development must take place in moist habitats, usually water.
Reproduction, Development, Metamorphosis • Some anurans have nests on land that are kept moist by a foam covering or by being near water.
Reproduction, Development, Metamorphosis • The main exception to external fertilization are the salamanders. • All caecilians have internal fertilization and about 75% have internal development. • Amphibian development usually includes larval stages called tadpoles. • Tadpoles are different from adults in how they breathe, how they move, and what they eat. • This helps reduce competition between adults and larvae.
Reproduction, Development, Metamorphosis • Reproductive activity is often controlled by outside factors such as temperature (in temperate regions) and seasons (such as the rainy season in tropical regions). • Courtship behavior helps individuals locate breeding sites and identify potential mates. • Salamanders rely mostly on smell and vision clues in courtship and mating. • Anurans, especially males, rely on sound.
Reproduction, Development, Metamorphosis • Sound production is mainly used in male anurans. • These sounds will attract females and let other males know that a certain territory is taken. • These sounds are species specific. • Females respond by making the same call that indicates her willingness to mate. • Release calls let a frog know that the partner is incapable of reproducing. • Distress calls are associated with pain or with being seized by a predator. • Sound production in frogs comes from the larynx and vocal cords. • Males also have a vocal sac.
Reproduction, Development, Metamorphosis • Parental care increases the chance of any one egg surviving but requires a lot of energy from the parent. • The most common form of care is protecting the egg clutch, usually done by either parent. • Maternal care occurs in species with internal fertilization (salamanders and caecilians), and paternal care may occur in species with external fertilization (anurans). • This care may involve providing oxygen to aquatic eggs, cleaning and/or moistening land eggs, protecting eggs from predators, or removing dead or infected eggs.
Reproduction, Development, Metamorphosis • Eggs may be transported if development occurs on land. • Females of genus Pipa carry eggs on their back. • Rheobatrachus females grow tadpoles in their stomach, and the young emerge from the female’s mouth.
Reproduction, Development, Metamorphosis • Metamorphosis is a series of abrupt structural, physiological, and behavior changes that transform a larva into an adult. • Several conditions influence the time required for metamorphosis, such as crowding and food availability. • Most changes, however, are controlled by hormones.
Reproduction, Development, Metamorphosis • Caecilian and salamander changes are minimal. • They develop reproductive structures, lose their gills and caudal fin. • Anurans have dramatic changes. • Limbs and lungs develop, tail is reabsorbed, skin thickens, and noticeable changes in the head and digestive tract occur.
