Class Amphibia

Chapter 25

Accommodations to land

1. Oxygen content: oxygen is 20x more abundant in air and diffuses more rapidly through air than water

2. Air density: provides little support against gravity-had to develop strong limbs and remodeled skeleton

3. Temperature regulation: air fluctuates more than water does and therefore experience more harsh and unpredictable conditions

4. Habitat diversity: variety of habitats provides safe shelter for protection of young

Tetrapods

Group of vertebrates that includes amphibians, reptiles, birds and mammals

Characteristics of modern amphibians

1. Usually 4 limbs (tetrapod)

2. Skin smooth and moist with many glands

3. 3 chambered heart (2 atria and one ventricle)

4. Ectothermal

5. Sexes separate

6. Moderately yolky eggs with jellylike membrane coverings

3 Orders

Comprise more than 5400 species1. Caecilians: Order Gymnophiona

1. Contains approximately 160 species of elongate, limbless, burrowing creatures commonly called caecilians

2. Occur in tropical forests of S. America, Africa, and SE Asia

3. Posses a long slender body, small scales in the skin of some, many vertibrae, long ribs, no limbs, and a terminal anus

4. Eyes are small, and most species are totally blind as adults

5. Special sensory tentacles on the snout

Caecilians

Food consists mostly of worms and small invertebrates

Fertilization is internal and males have a protrusible copulatory organ

Eggs are usually deposited in moist ground near water

Larvae may be aquatic or complete larval development may occur in the egg

In some species eggs are carefully guarded during their development in folds of the body

Salamanders: Order Urodela

Consists of tailed amphibians, approximately 500 species

Occur in almost all northern temperate regions of the work

Most have limbs set at right angles to their body, with forelimbs and hindlimbs of approximately equal size

Carnivorous both as larvae and adult, preying on worms and small arthropods or mollusks

Most eat only animals that are moving Ectothermic (cold blooded)

Salamander breeding

Fertilized internally (a female recovers in her cloaca a packet of sperm-spermatophore-deposited by a male on a leaf or stick

Red spotted newt

Aquatic larve metamorphose into a brightly colored “red eft” stage, which remains on land from 1-3 years before transforming into a secondarily aquatic adult

Dusky salamander

Female dusky salamander attending eggs, which includes rotating eggs and protecting them from fungal infections and predation by various arthropods and other salamanders

Salamander respiration

General amphibian condition of having the ability to exchange oxygen and carbon dioxide across their skin

Longtail salamander

Frogs and Toads: Order Anura

More than 4840 species of frogs and toads

A. Bullfrog, largest American frog and the mainstay of the frog-leg market

B. Green tree frog, inhabitant of the swamps in SE USA

Frogs and Toads

Smallest measures less than 1cm in length-can be covered by a dime Live in Cuba and Brazilian

rainforest Largest is the West

African Conraua goliath, more than 30 cm long from tip of nose to anus Eats rats and ducks

Frogs and Toads

Toads Have short legs Stout bodies Thick skins Usually prominent

warts

American toad feasts on insects, snails, and earthworms

The rough skin contains numerous glands that produce a milky fluid, providing excellent protection from a variety of potential predators

African clawed frog

Frog has been introduced to California, where it is considered a serious pest

Eat or be eaten

Snakes, aquatic birds, turtles, raccoons, and humans prey on frogs

Fish prey on tadpoles Frogs & toads in tropics are aggressive, jump

and bite at predators Most can inflate lungs so they are difficult to

swallow When held, they will leap violently, voiding its

urine Some have poison glands in their skin

Frog skin

Frogs have 2 layers: Epidermis and dermis Epidermis contains ketatin, a protein that provides

protection against abrasion and loss of water Epidermis contains mucous glands secrete a protective

mucous waterproofing the skin surface Serous glands produce a whitish watery poison highly

irritating to predators All amphibians produce a skin poison, but its effects

vary from species to species and with different predators

Gray Tree frog

Cryptic coloration: so good that the presence of this frog usually is disclosed only at night by its resonant flutelike call

Respiration

Use 3 respiratory surfaces for gas exchange in air Skin (cutaneous breathing) Mouth (buccal breathing) Lungs

Frogs and toads are more dependent on lung breathing than salamanders

Skin is important for gas exchange during hibernation

Frogs are positive-pressure breathers that fill their lungs by forcing air into them

A. Floor of mouth is lowered, drawing air in through nostrils

B. With nostrils closed and glottis opened, the frog forces air into its lungs by elevating floor of mouth

C. Mouth cavity rhythmically ventilates for a period

D. Lungs are emptied by contraction of body wall musculature and by elastic recoil of lungs

Vocalization

Both male and female frogs have vocal cords, but those of males are much better developed

Frog produces sound by passing air back and forth over the vocal cords between the lungs and a large pair of sacs (vocal pouches) in the floor of the mouth

Vocal pouches also serve as effective resonators in males, which are used to attract mates

Reproduction

Reproduction

Male green tree frog clasps a larger female during breeding season. Clasping is maintained until the female deposits her eggs. Like most tree frogs, these are capable of rapid and marked color changes. Male is usually green and has darkened during mating

Reproduction

Female S American pygmy marsupial frog carries developing larvae in a dorsal pouch

Reproduction

Female Surinam frog carries eggs embedded in specialized brooding pouches on the dorsum; froglets emerge and swim away when development is complete

Reproduction

Male poison arrow frogs carry tadpoles adhering to its back

Reproduction

Tadpoles of a male Darwin’s frog develop into froglets in its vocal pouch.

When ready to emerge, a froglet crawls into the parent’s mouth, which the parent opens to allow the froglets to escape