4 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.
5 EXTERNAL STRUCTURE AND MOVEMENT Chromatophores are specialized cells in the skin that are responsible for skin color and color changes.Cryptic coloration, aposematic coloration, and mimicry are all common in amphibians.
9 Support and MovementAnimals 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.
11 Support and MovementThe 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.
12 Support and MovementAmphibians 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.
13 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.
15 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.
17 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.
18 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.
20 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.
21 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.
22 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.
24 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.
26 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.
28 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.
29 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.
30 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.
32 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.
34 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.
35 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.
36 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.
37 Reproduction, Development, Metamorphosis Some anurans have nests on land that are kept moist by a foam covering or by being near water.
38 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.
39 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.
40 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.
42 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.
46 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.
49 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.
50 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.
52 AMPHIBIANS IN PERILFrogs and salamanders are disappearing at an alarming rate—and no one knows exactly why.Local events can affect populations—clear-cutting forests, mining, drilling, and urban sprawl destroy habitats.
53 AMPHIBIANS IN PERILTwo other factors are thought to be affecting amphibians—acid deposits and UV radiation.Embryos are very susceptible to changes in the pH of their water.UV radiation also kills eggs and embryos.