Amphibians

TETRAPODA

·       Amphibians and amniotes (birds, reptiles, and mammals)

·       Life originated from the water

·       Animals are still composed mostly of water

·       Most cellular activities require water

·       Terrestrial land area represents a relatively dangerous habitat for all life

·       Invasion of land required many modifications of organ systems to adjust to the transition

 

Important uses of water

  • Water regulates body temperature

  • Acts as a buffer against overheating

  • Moistens tissues in the eyes nose and mouth

  • Water regulates ph (measure of alkalinity, basicity, or acidity of bodily fluids)

  • Helps dissolve minerals and nutrients to make it accessible for the body

  • Water forms a majority of the mucus lining that protects the animal’s stomach

  • It protects the lining of the stomach from the corrosive action happening during digestion

  • Water activates the sodium bicarbonate layer

  • The first chemical digestion occurs in the mouth because of the saliva (which is made of water)

  • Water helps flush out waste products

  • Water is responsible for hydrolysis and energy production

  • Water lubricates joints

 

FROM WATER TO LAND

  • Movement: From water to land

  • Juvenile frog lives in watter and continues development on land as an adult

  • Frog

·       Masses of eggs > limbless, gill-breathing, fish-like tadpole larvae that feed and grow in the water

·       Change starts

·       Appearance of hindlegs

·       Shortening of tail

·       Loss of larval teeth and gills

·       Development of eyelids 

·       Emergence of forelimbs

·       Amplexus – mating behavior where males clasps into the females

  • Amphibians – includes the living vertebrates that have transitioned from water to land

·       Even after 350M years of evolution, they remain quasiterrestrial

·       They are ectothermic

·       They depend on water for reproduction

  • Some salamanders have retained aquatic morphology permanently

  • Terrestrial amphibians have thin skin that loses water rapidly. This results to them being restricted to moist habitat

  • Most amphibians require moderately cool habitats as they are ectotherms

  • Cool and wet areas are important for reproduction, since eggs easily desiccate and must be shed into water or kept moist

 


CAECILIANS

·       Order Gymnophiona

·       About 200 living species of elongate, limbless, and burrowing animals

·       Inhabit tropical forests in S.A, Africa, India, and SEA

·       They are usually aquatic or hidden in the soul

·       Ichthyopis mindanaoensis – Todaya caecilian 

 

SALAMANDERS

·       Order Urodela (Caudata)

·       Most are small under 15 cm long

·       Approximately 700 living species

·       Some are capable of growing more than 1.5 m like the Japanese giant salamander

·       Aquatic species lay eggs in clusters or stringy masses and hatch into aquatic larvae with external gills and finlike tails

·       American newts have aquatic larvae that change into terrestrial juvenile which later metamorphose into secondary aquatic adults

·       Completely terrestrial species deposit eggs in small grape like clusters under logs or in sioft eaht 

 

Salamander respiration

  • Extensive vascular nets in skin that exchange both oxygen and carbon dioxide

  • External gills, lings, both gills and lungs,or neither

  • Salamanders with aquatic stages hatch qith gills which are then liost at metamorphosis

 

Paedomorphosis

  • An alternative process to metamorphosis

  • Frequent in newts and salamanders

  • Salamanders retaiuns some pre-adult features of ancestores as they reach adulthood

 

ANURANS

·       Frogs and Toads

·       Order anura (Salientia)

·       Approximately 6600 species of frogs and toads that date back to the jurassic period

·       Most live near water source since reproduction requires water and skin is water permeable

·       All have a tailed larval stage and taillless jumping adult form

·       Thin skin allows them to respire through their skin

·       Pimrary organ for respiration is the lungs

·       There are approximately 45 families of frogs and toads

 

Family Ranidae: Common frogs

Family Hylidae: Tree frogs

Family Bufonidae: Toads

 

Anuran habitats

  • Habitats and distribution is quite diverse and extensive

  • Ranidae – common in temperate and tropical regions

  • Wood frogs spend ost of its time on damp forest floors and retuirsn to pools for breeding

  • Buul forgs and green frogs occur in near permanent water and swamps

 

Defenses

  • During hibernation, life processes are sustained by diffusion of oxygen through skin and energy comes from fat and glycogen stored during spring and summer

  • Tree frogs hibernate in the humus of forest floors, can toelrate low temps and may survive freesing up to 35 percent of body fluids

  • Other species pretend to be dead 

  • Some can expand their lungs, making them difficult for predators to swallow

  • There are some poisonous species

 

Integument and coloration

  • Frog integument and coloration are unique and highly adaptive

  • Frog skin is thin, moist and attached loosely to the body but attached well to the region where the hindlimbs, forelimbs, are connected to the joints

  • Epidermal layer has keratin ( a though and fibrous protein that is shed periodically) 

  • Terrestrial amphibians have heavier deposits of keratin

  • Amphibian keratin is soft compared to that of mammals and birds

 

Amphibian skin

  • Mucuous glands secrete protective waterproofing

  • Large granular glands are present, which produce a whitish watery poison that is irritating to predators

 

Chromatophores

  • Specialized skin pigments

  • Xanthophores – located in the upper region of dermis and are yeloow, orange, or red pigments

  • Iridophores – are silvery light reflecting pigments act like tiny mirrors

  • Are in the middle region

  • Work with xanthophores to prduice bright collors of most tropical frogs

  • Melanophores are in the lower region of the dermis and contain the black or brown melanin

  • Cytoplasmic streaming carries the pigments around

 

Amphibian respiration

  • Skin provides cutaneous breathing

  • Mouth provides buccal breathing

  • Lungs are usually present in adults

  • Lungs are supploed by pulmonary arteries and blood is returned to the left atrium by pulmonary veins

 

Frog vocalization

  • Vocalization results from vocal cords in the larynx

·       These are much more developed in males than females

  • Sound is produced when air is passed back and forth over vocal cords between the lungs to a large pair of viocal sacs or puhces in the floor of the mouth

  • The sacs also serve as resonating chambers that males use to attract mates

  • Each species has a unique sound pattern

 

Circulatory system

  • Frogs have a closed CS with a single pressure pump, the heart, moving blood through the peripheral network of arteries and veins

 


 

Feeding

  • Most adult frogs are carnivorus

  • They actch prey with a protrusible tongue

  • Glandular free end have sticky secretion that adheres to prey

  • Any teeth that are present function to hold prey and are not for chewing

  • The carnivorous adults have short digestive tract that produces enzymes for digesting carbohydrates, fats, and proteins

  • Tadpoles were mainly herbivorous with longer tracts

 

Frog ear

  • Tympanic membrane

 


 

Vision

  • Numerous adaptations to aquatic eyes helped them adapt for use on land

  • Lachrymal glands and eyelids keep the eyes moist free of dust and protected from injury