Amphibians: The Dual Masters

Amphibia is a class of vertebrates that includes frogs. Toads, salamanders newts, and cycads. Amphibians have ectothermic, tetrapod eggs that are not covered by membranes. Adults lay their eggs in water, from which the larvae with gills are able to emerge and metamorphose into adult lungs. Mudpuppies, olms and other amphibians retain their larval gills for the duration of their lives. Adults are known to breathe through skin. In the subclass Lissamphibia, there are three modern amphibian orders: Anura (Anura), Caudata (Caudata) and Gymnophiona. Approximately 6,500 amphibian species are known. They look like reptiles, but they are different. Repltiles and birds as well as mammals and other mammals have protective membranes around their eggs. Batrachology is the study of amphibians. They are important ecological indicators because many of them are in danger of extinction. Early amphibians evolved from Sacrcopterygians in the Devonian Period. They became dominant and diversified during the Carboniferous Period and Permian Period, but were then replaced by birds, mammals and reptiles.

The term amphibian is derived from the ancient Greek for dual life. Initially, the term was used to describe animals that lived both on land as well as in water such a seals and otters. In 1919, the scientific classification was introduced and this term was only used for amphibians. The amphibians are vertebrates that have four legs. They are mostly found in freshwater environments, not marine ones. However, there are a few frogs who live in brackish waters and mangrove swamps. The eggs are encased in a gelatinous coating that swells up when it comes into contact with water. Larvae hatching from eggs have a different form than adults. Tadpoles are called frogs or toads, and they have a large head and a dorsoventrally rounded tail. The tadpoles have no limbs, breathe with gills, and are herbivores. Later on they will lose these structures and metamorphose to become carnivores. Salamanders and newts have long bodies with feathery gills. They are carnivorous due to the fact that the front legs of these creatures develop sooner than their hind legs. Like frogs, toads do not undergo metamorphosis. Caecilians reproduce in moist burrows or lay eggs.

Amphibians have cold blooded organisms which maintain their body temperatures above their surrounding environment. This allows them to survive in higher temperatures. The species that live in different areas are very sensitive. During the winter, many species hibernate to avoid extinction. Many species hibernate for over half the year in colder climates. In hot summer months, many species undergo aestivation in the cool mud beneath the dried ponds to avoid the heat. Their cold blooded nature allows them to survive during prolonged periods of starvation.

Integumentary system

Amphibian skin is water permeable and contains numerous glands of mucus which prevents the skin from drying. Amphibians can breathe better when their skin facilitates gaseous interchange. To protect the skin from predators, many amphibians evolved poison glands on the surface of their skin. The toxicity of these glands can vary depending on the species. Some amphibians secrete toxins that are deadly to humans, but others have only a mild or very small effect. The paratoid toxins glands are found behind the ears and eyes of some frogs, toads and salamanders.

The presence of dynamic structures characteristic of vertebrates, such as the presence of outer layers with a high degree of cornification that are subject to regular moulting is a sign of the integumentary system. This process is controlled and regulated by hormones produced by the thyroid and pituitary glands. Toads have warts, or thickenings in the local area. In mammals and birds, the outer layer of skin is shed regularly in one piece. They also eat this sloughed-off skin. Amphibians’ skin color is determined by chroomatophores, also called pigment cells. They are arranged into three layers. Melaophores are usually found in the three layers, along with guanophores and lipsophores. Pituitary glands are responsible for the change in coloration of many species. A very bright color is a sign that the skin has a lot of poison glands.

Skeletal system

The skeletal structure of amphibians can be compared to that of other tetrapods, but there are many differences. The skeletal structure includes a cranium and spine. Long bones such as humerus, femur, and short bones, like phalanges. The majority of amphibians have four legs, except for the caecilians. Bones have a hollow structure and are light. The shoulder girdle was built strictly according to the ancestral plan. The pelvic girdle, which is more developed, is made up of three bones, namely ilium (the iliac bone), ischium (the ischium bone) and acetabulum.

Circulatory system and nervous system

The circulatory systems of adults and juveniles are completely different. The juveniles have gills for oxygenating the blood, and the movement of the gills is similar to fishes. As gills disappear, lungs are the main respiratory structure in adults. The heart is made up of two atria and a ventricle that pumps oxygenated blood to the lungs through the arteries, and deoxygenated through the veins. They are cold blooded, but they maintain homeostasis. The nervous system of vertebrates is composed of a spinal cord, a brain and nerves that extend throughout the body. The brain is not as developed as that of reptiles and birds. The olfactory lobe, which is responsible for smell, is highly developed. Cerebrum controls behavior and learning. The cerebellum controls muscle contraction and the optic lobes control learning. Medulla oblongata controls heart rate and breathing. To control body functions, the brain sends messages to the spinal cord. The pineal gland releases hormones that are responsible for aestivation, and hibernation taphibians.

Digestive system and excretory system

Amphibians have large, voluminous stomachs because they swallow their prey whole. The esophagus is separated from the stomach and oral cavity by sphincters. It is known that the glands that line the esophagus secrete pepsin and mucus. The Pyloric Sphincter is the sphincter that separates stomach and intestine. The duodenum is responsible for the transport of food into the intestine from the stomach. Amphibians possess a pancreas as well as bile and liver. The liver is responsible for all vital metabolic functions in mammals. In the small intestinal tract, carbohydrates, fats, and proteins are digested. The large intestine is where salt and water are absorbed. Fecal material then passes out of the cloaca. Two kidneys are located on the dorsal roof of the body and they participate in excretion.

Respiratory system

The lungs have a primitive structure with few septa, and fewer alveoli that diffuse oxygen slowly. Ventilation is assisted by buccal pumping. The majority of amphibians can exchange gases through their skins, either by using water or air. The skin must be moistened to facilitate cutaneous breathing. Some small species, such as plethodontids without gills or lungs, can only rely on cutaneous exchange in air where oxygen concentration is higher. In their larval stage, most salamanders lose their gills as they grow up. However, some species prefer to keep their larval gills.

Sensory systems

Amphibians have eyelids with glands and ducts. These eyes are an improvement on invertebrate ones, allowing for color vision and depth of focus. Retina has green rods which are sensitive to a wide range of wavelengths. Frogs have external eardrums or tympani located just behind their eyes. The ear has a patch called amphibiorum, which is only found in amphibians. It can detect low-frequency sounds. The presence of the columella-opercular system is another unique feature. It is responsible for transmitting airborne and seismological signals. The complex uses sound to communicate. They need fresh water to reproduce, but only a few of them require brackish. The development of the tadpoles is indirect, as they lay eggs. They are very good parents and adopt unique and different ways to take care of their young. The thyroxin levels in the blood are responsible for amphibians’ metamorphosis.

Vocalization

The newts, caecilians, and salamanders make soft squeals and grunts. Frogs and toads use mating calls to attract mates during breeding season. Each call has a purpose and is used to detect the species. It is important that males and females find the right mate to reproduce in ponds with many species. Sometimes, calling sounds increase the likelihood of a predator attacking. The sound produced by the birds during breeding season is slightly different. Vocal sacs, which are modifications of the larynx, produce the sound.

Defence

Amphibians are generally helpless and have soft bodies. Birds and other animals can easily catch them while they are walking on land, and fish can capture them in the water. They hide during the day to avoid predators and then come out at night. Some species use camouflage to hide, while others have poison glands. Like the fire-bellied salamander, poisonous species have a bright yellowish black colour.

The new species of frogs in India

Scientists have been listening to frogs croak for many years. Their hard work has yielded fruitful results. They discovered 12 new frog species from India, and three others that are classified as extinct. A report by Global World Conservation states that 32% of amphibian species are threatened due to habitat destruction and environmental pollution. The meowing nightfrog, whose croaking sound is similar to that of a cat’s, is one of the twelve new species. Another is the jog frog in which both the male and female are known to care for the egg. And the last is the Wayanad frog. It grows up to the size of a baseball or cricket ball. The other species were rediscovered in India, and their findings have been published on September 15th by Zootaxa.