Amphibians Chapter 40 (798-814)
Objective 40.1 • Describe three preadaptations involved in the transition from aquatic to terrestrial life • Describe two similarities between amphibians and lobe-finned fishes • List five characteristics of living amphibians • Name the three orders of living amphibians and give an example of each
Origin and evolution of amphibians About 360 million years ago, amphibians became the first vertebrates to live on land. The name amphibian comes from the Greek word meaning “double” and “life” and reflects the fact that many amphibians spend part of their life on land and part in water.
Adaptation to land • Most likely evolved from lobe-finned fishes • Preadaptatins are adaptations in an ancestral group that allow a shift to new functions which are later favored by natural selection • Fins had bone structure to walk as legs • Modified pouches in digestive track lungs
Characteristics of early amphibians • Skull and vertebra column, bones in fin and (similar) • Scarcopterygian- extinct lobe-finned fish • 360million years fossil record • Had 4 strong limbs • Gills, teeth, lateral lines • Most likely spent most time in water
Diversification of amphibians • Devonian period and carboniferous period amphibians split into 2 main evolutionary lines • One modern amphibians • Ancestors of reptiles • 4500 species of amphibians 3 orders of amphibians • O. Anura – frogs and toads (3900 species) • O. Caudata- salamanders (400 species) • O. Gymnophiona – caecilians (legless tropical)
Modern Amphibians • Aquatic larval to terrestrial adult (metamorphosis) • Moist thick skin with no scales • Feet- lack claws, webbed • Gills, lungs, skin in respiration • Eggs lack muticellular membranes or shells • Eggs laid in water- external fertilization
Objective 40.2 • Relate the structure of amphibians skin to the types of habitats in which amphibians can survive • Identify three adaptations for the life on land shown by the skeleton of a frog • Sequence the flow of blood through an amphibian’s heart • Describe the digestive/ excretory systems • Discuss the nervous system
Characteristics of amphibians As you have already seen, terrestrial vertebrates face challenges that are far different from those faced by aquatic vertebrates. In this section you will learn about some of the ways amphibians meet the challenges of living on land.
skin Two important functions • Respiration • Protection • Moist, permeable to gases and water • Numerous mucous glands keeps skin moist • Can also secrete- foul taste/ poison • Live in moist areas • Tend to be active at night • Can be affected by environment (indicators)
skeleton • Strong internal skeleton • Bear weight of body • Strong limbs to support body • Ability to jump and land
Circulatory system 2 separate loops • Pulmonary circulation- carries deoxygenated blood from heart to lungs and back to heart • Systemic circulation- carries oxygenated blood from the heart to the body and back to the heart 3 chambered heart
Respiration • Larval by gills and skin • Adult – lungs (pulmonary respiration) and skin (cutaneous respiration) • Positive pressure breathing- pumps air into the lungs
Digestive system • Carnivorous • Small insects, arthropods, mice, snakes, fish, amphibians, birds • Larva- herbivores (algae, bacteria, plants) • Pharynx esophagous stomach liver gallbladder small intestine large cloaca
Excretory system • Kidney (primary) filter nitrogen and waste • Flushed out as urine • Kidney urinary ducts cloaca urinary bladder (water storage) can be reabsorbed during dry times • Transform ammonia into urea
Nervous system • Brain (same size as fish) • Olfactory lobes (sense of smell) • Long lobes of cerebrum (behavior learning) • Optic lobes – process info from eyes • Cerebellum- muscular coordination • Medulla oblongata- organ functions, heart • 10 pairs of cranial nerves
Sense organs • Lateral lines (only in water) • Nicitating membrane- covering of eyes • Tympanic membrane- eardrum • Columella- small bone that extends between the tympanic membrane and the inner ear
Objective 40.3 • Explain how a male frog attracts a female of the same species • Discuss the reproductive system in frogs • Describe the changes that occur during metamorphosis in frogs • Identify two examples of parental care in amphibians
Reproduction in amphibians • One of the biggest differences between aquatic and terrestrial life-forms is their method of reproduction. Most amphibians depend on water for reproduction. They lay their eggs in water and spend the early part of their lives as aquatic larvae.
Courtship and fertilization • Mating call- frogs croak • Males have vocal sacs • Female responds to same species • External fertilization • Eggs tadpoles hind legs appear frog legs appear young frog adult • Thyroxine – produced by thyroid gland to stimulate metamorphosis
Parental care • Parent care can increase chances of survival • Male remain with eggs • Rhinoderma darwinni- takes them in vocal sacs till hatch • Gastric –brooding frogs in Australia- swallow eggs • Eleutherodactylus- sit on eggs
Virtual Dissections • http://www.mhhe.com/biosci/genbio/virtual_labs/BL_16/BL_16.html