Amphibians

1. Bio II Rupp Amphibians

2. Background • Evolved 370 mya from sarcopterygii • Name means “double” “life”

3. Adaptation to Land • Bad hypothesis • Movement overland from shrinking pools of water to larger pools • Short overland crossing do not allow time for change • Better hypothesis • Escape from predation and competition to land where resources were plentiful—insects and plants

4. Characteristics of Early Amphibians • Similar to sarcopterygii • Skull • Limbs • Shape

5. Icthyostega continued • Four strong limbs—homologous to pectoral fins • Lung breather • Teeth for eating fish • Seven toes on hind foot—today’s amphibians have five

8. Diversification • Evolutionary split in the Devonian and Carboniferous period • One line became modern amphibians

9. Diversification continued • Other line was forerunner to modern reptiles • Approximately 4500 species of amphibian today • Anura—3000 species • Urodela—400 species • Apoda—160 species

10. Modern Characteristics

11. Aquatic Larva to Terrestrial Adult--Metamorphosis

12. Moist, thin, scaleless skin

13. Claw-free feet, typically webbed

14. Gills, lungs, and skin for respiration

15. No multicellular egg membranes

16. Large mouth with upper and lower teeth

17. Three-chambered heart

18. Ectothermal

19. Paired kidneys

20. Ten pairs of cranial nerves

21. Separate Sexes

22. Order Anura • Name means “without tail” • Frogs and toads • Found worldwide except polar regions • Toads = rough and bumpy skin • Frogs = smooth and moist skin • Spend at least part of their life in water, some are totally aquatic • Built to jump • Long, strong hind legs • Short, shock absorbing forelimbs • Eat almost anything • Return to water for fertilization and mating • Larval tadpole stage

23. Toad versus Frog

24. Order Urodela • Tailed amphibians • Elongate body, long tail, moist skin, four limbs • Few centimeters to 1.5 meters long • Carnivorous • Typically nocturnal • Found in the Americas, Africa, Asia, and Europe • Many lay eggs in water—metamorphosis • Family Plethodontidae is the largest group—lungless, gas exchange through skin • Terrestrials hatch into mini adults—direct development • Internal fertilization—spermatophore • Some females retain eggs until hatching • Necturus

25. Urodelans

26. Urodelans

27. Urodelans continued • Paedomorphosis—retention of pre-adult structures • Non-metamorphic species are termed perennibranchiate

28. Apodans • Name means “without feet” • Typically called caecilians • Resemble snakes • Average 30cm in length some reach 1.5m • Small eyes located under skin or bone—typically blind • Burrowers • Relatively little is known • Teeth for prey capture • Chemosensory tentacles on head • Believed to have internal fertilization • Some females stay with eggs until hatching • Some are viviparous • Found in Asia, Africa, and S. American tropical regions

29. Apodans continued

30. External Covering • Two major functions • Respiration • Protection • Gas exchange is aided by mucous glands to keep the skin moist

31. External covering continued • May secrete poisons • May desiccate quickly if not near water • Nocturnal to avoid desiccation

32. Internal Anatomy • Strong vertebral column to support weight on land • Strong limbs • Pectoral and pelvic girdles • Cervical vertebrae for neck movement

33. Internal Anatomy—circulatory system • Double circulation—two loops • Pulmonary circulation—carries deoxygenated blood from heart to lungs • Systemic circulation—carries oxygenated blood to body • Faster blood flow than a single loop system like fish

34. Internal Anatomy—circulatory system continued

35. Internal Anatomy—circulatory system continued • First division in pulmonary and systemic pumping • Deoxygenated blood enters sinus venosus of right atria • Oxygenated blood enters left atria • Blood enters the ventricle—structure minimizes mixing of bloods • Conus arteriosus valve separates blood and sends to lungs or body

36. Respiration • Larval amphibians use skin and gills • Adults use skin and lungs • Cutaneous respiration is important due to small surface area of lungs • Positive pressure breathing • The mouth changes the pressure in the airway • Nostrils control direction of the airflow

37. Respiration continued

38. Digestive system • Adults are carnivorous • Larvae are typically herbivorous • Organs • Pharynx • Esophagus • Stomach • Liver • Gall bladder • Small intestine • Large intestine • Cloaca

39. Digestive system continued • Elastic stomach and esophagus allow swallowing of large prey • Stomach secretes gastric juices • Pyloric sphincter allows digested food to move to the small intestine • Upper portion of small intestine is the duodenum • Middle portion of the small intestine is the ileum

40. Digestive system continued • Mesentery holds the small intestine together • Digested food, urinary wastes, and eggs and sperm pass into the cloaca before exiting the vent • Liver produces bile stored in the gall bladder • Pancreas secretes enzymes to help break down food in the small intestine

43. Excretory system • Kidneys are the primary organ • One located on each side of the spine • Filter nitrogenous wastes, mix with water, and excrete as urine • Kidneys to urinary ducts to urinary bladder • Bladder can serve as a water reservoir organ in dry times • Larval amphibians excrete ammonia which is toxic • Adults transform ammonia into urea, which is less toxic and conserves water

44. Excretory system continued

45. Nervous system • Brain is divided into lobes • Olfactory • Cerebrum—behavior and learning • Optic lobes • Cerebellum—muscular coordination, not well developed • Medulla oblongata—involuntary muscle control, heart and breathing • Ten pairs of cranial nerves • Spinal cord and PNS

48. Sense organs • Larval amphibians have a lateral line system like a fish—it is lost during metamorphosis

49. Sense organs continued • Eyes • Covered by nictitating membrane • Large optic lobes

50. Sense organs continued • Hearing • Tympanic membrane—external eardrum • Columella—small bone between typanum and internal ear • Inner ear fluid carries vibrations from columella • Sounds are converted to electrical impulses by small hair cells • Electrical impulses are transmitted to the brain