Amphibians Zoology Wakefield – 2011-2012

1. Amphibians Zoology Wakefield – 2011-2012

2. Amphibians Originated from the Devonian period About 360 mya 5400 Species

3. Amphibians General Characteristics Endoskeleton made of bone Bilateral body plan with tetrapod limb arrangement Webbed feet are often present No true claws or nails Body forms vary from an elongated trunk with a distinct head to a compact, body with a fused head and trunk and no neck I.

4. Epidermis is thin & moist with mucous and poison glands. Skin is very think & abundantly supplied with blood vessels • Respiration is by lungs, skin & gills (in larval form) • Circulation is closed with a 3 chambered heart • 2 atria and 1 ventricle • (spiral valve partially divides it)

5. Body temperature is controlled ecto-thermically • Excretory system is paired dorsal kidneys • Reproduction is dioecious with fertilization mostly external in frogs & toads; mostly internal with salamanders & caecilians. Predominantly oviparous some ovoviviparous

6. Development usually includes an aquatic larval stage, then metamorphoses to the adult form which is usually terrestrial but a few are totally aquatic • All amphibians retain a dependence on water for the completion of their life cycle hence the meaning of Amphibia, double - life

7. Movement onto land – four Important modifications: • Development of lungs to extract oxygen from air which is 1000X less dense than water • Develop strong limbs for body support – without density of water to support the body weight movement became a problem • Develop temperature regulation because air temperature fluctuates much more rapidly than water temperature. Terrestrial environments experience harsh and unpredictable cycles of freezing, thawing, flooding and drying • Ability to exploit new habitats; to find shelter for vulnerable eggs or youngmay be easier on land than in the water

8. Three Living Amphibian Orders Order Gymnophiona (means naked snake) (aka Apoda) Example Caecilians (160 species)

9. Order Gymnophiona (means naked snake) Limbless, burrowing creatures commonly called Caecilians Found in South America, Africa, and SE Asia Most are totally blind as adults Since they live underground, they are rarely seen by humans Their food is mainly worms and other invertebrates

10. Order Caudata (means with tail) (aka Urodela) Example: Salamanders (around 500 species – about 350 North American species)

11. Order Caudata (means with tail) Found in all temperate regions of the world Most are small, less than 15cm but the giant JapaneseSalamander may exceed 1.5 meters in length Salamanders are carnivorous in both adult and larval forms

12. Order Caudata (means with tail) (aka Urodela) Breeding behavior-fertilization is usually internal with the female picking up a spermatophore packet with their cloacal vent that was left on a leaf or a stick by a male

13. Order Caudata (means with tail) (aka Urodela) Some terrestrial species have direct development in which the larval stage is bypassed and the young hatch as miniature versions of their parents Some species of salamanders exhibit paedomorphosis which is the ability to retain some larval characteristics (such as gills) while becoming sexually mature. Example: mud puppy

14. Order Caudata (means with a tail) Some salamanders, such as the Mexican Axolotl exhibit a condition called Neoteny in which they remain in the larval form until environmental trigger them to undergo metamorphosis and develop into adults. They can breed as the larval or adult forms.

15. Order Anura ( means without tail) Example: frogs and toads (4840 species)

16. Order Anura ( means without tail) Frogs & toads are divided into 21 families with the best know genus of frogs being Ranidae and the best know genus of toads Bufonidae

17. Order Anura ( means without tail) Toad’s warts are actually poison glandsunder the skin The largest Anuran is the African goliath frog, over 30 cm eating animals as large as cats and dogs, rats, & ducks

18. Order Anura ( means without tail) The smallest is the Brazilian rain forest frog less than 1 cm

19. Order Anura ( means without tail) The largest North American frog is the bullfrog – Ranacatesbeiana

20. Order Anura ( means without tail) Life Cycles – All frogs & toads practice external fertilization Number of eggs laid vary from 2 to 20,000 Males grip & squeeze the females to aid in egg expulsion; this is amplexus; the male then discharges a cloud of sperm over the eggs to fertilize them. Eggs hatch into tadpoles in 2-21 days Transformation from a tadpole into an adult anuran varies from 3 months for a Leopard frog to 3 years for a bullfrog. Some desert toads metamorph in as little as 12 days

21. Order Anura ( means without tail) Amphibian Skin – All amphibians produce toxins but its effectiveness varies from mildly caustic to the extremely toxic poison of three species of small South American Phyllobate frogs that are the most lethal animal toxins known; more poisonous than the venom of sea snakes or the most dangerous arachnid

22. Order Anura ( means without tail) Amphibian Skin – Gas exchange by the skin’s surface is very important for anurans; this is called cutaneous breathing; CO2 is lost primarily by the skin while oxygen is absorbed by the lungs

23. Order Anura ( means without tail) Feeding & Digestion Anurans will feed on anything that moves and can be swallowed whole They snap @ moving prey with their protrusible tongue that is attached at the front of their mouth. Most anurans have a set of teeth in the roof of the mouth called volmerine teeth; these are not for biting or chewing but to pierce prey until it can be swallowed whole. Anurans swallow by pressing down with prominent eyeballs and pressing upward with the tongue Larval stages of anurans are usually herbivorous feeding on pond algae and other vegetable matter (tadpole stage)

24. Order Anura ( means without tail) Senses – The sense of smell is an important sense in anurans The most dominant sense in anurans is vision with a set of rods & cones for full color sight. They have eyelids and a nictating membrane to protect the eye

25. Order Anura ( means without tail) Senses – Anurans have a simple ear structure that is sensitive to low frequencies mainly in the 100-200 hz range

26. Order Anura ( means without tail) Senses – Other senses include touch, taste, and color which change due to chemoreceptors in the skin (due to changes in temp, chemicals, or even mood)