Mr. Bouyer

Day 1 - 2 | Day 3 | Days 4 - 7 | Reading Assignment

Describe the characteristics of the Class Amphibia. Know at least one Texas representative from each of the three amphibian orders. Compare hibernating and estivating. Use a dichotomous key to identify Texas amphibian Orders.

Animal Identification Assignment.

How do the foods of frogs and tadpoles compare?

Class characteristics:

Smooth, moist skin (no scales)
Toes lack claws
Gills, lungs, and skin used in respiration
Metamorphosis from aquatic larval stage to adult form
Larvae heart 2-chambered, adult heart 3-chambered
Eggs fertilized externally

There are three orders of living amphibians containing about 170 genera. The majority of amphibians are found in tropical regions with abundant rainfall. Correlated with the moisture requirement of amphibians is the fact that most forms are nocturnal.

The class name means "two lives", indicating that amphibians are able to survive both in water and on land. They represent an important step in the phylogeny of vertebrates, the bridge from water onto land. No amphibians live in the ocean, but some will tolerate brackish water.

Amphibian lungs are poorly efficient. For this reason, most amphibians also use their moist skin for respiration. Temperature is another key factor in the life of amphibians. Being ectothermic, their body temperature changes with the environment. Temperature extremes are deadly to amphibians. Toads will burrow below the frost line to escape winter temperatures and many frogs and salamanders will hibernate in the mud at the bottom of rivers and lakes. Some species actually produce glycerol, a type of "antifreeze", in their cells to resist ice crystal formation.

Hot, dry conditions are just as deadly. Many species of amphibian will escape these conditions by estivating, the summer equivalent of winter hibernation. They conserve body moisture by retreating into a moist burrow or crevice, curling tightly and remaining inactive, torpid, until better conditions return. Some even secrete a lipid, fatty substance, and coat their body to prevent water loss during this period of inactivity.

All amphibians must reproduce in the water or very wet soil. Their eggs are covered with only a thin membrane that is permeable to water. For this reason, amphibian eggs cannot survive out of the water.

You are familiar with the metamorphosis of frogs and toads from egg to tadpole to adult. The tadpole stage has gills and feeds only on plants. During the metamorphosis, lungs form and the digestive system changes to that of a carnivore.

The most common frogs and toads on Texas are represented in these families:

• Family Hylidae - tree frogs
  • Hyla cinerea - green tree frog
  • Hyla crucifer - spring peeper
  • Acris gryllus - cricket frog
• Family Ranidae - true frogs
  • Rana pipiens - leopard frog
  • R. catesbeiana - bullfrog
• Family Bufonidae - the largest family of toads
  • Bufo americanus - American toad

Most salamanders are terrestrial animals, spending almost all of their time on land. Their skin is subject to water loss just like all other amphibians, so their common habitat is in moist soil under rocks and logs.

A "tadpole" salamander is pictured on the right. Most salamanders go through a metamorphosis similar to frogs and toads. But there are exceptions. Neoteny is the prolonged retention of larval body features to the point where reproduction occurs in larva-like individuals.

• Facultative neotenic - metamorphosis may or may not take place.
• Obligate neotenic - metamorphosis never takes place.

By remaining in the aquatic form, the animal exploits its aquatic environment as long as food and other favorable conditions last. Research indicates that neoteny occurs because the hypothalamus of the brain fails to produce the hormone that causes the pituitary to stimulate the thyroid gland to produce growth hormones that trigger metamorphosis. Some scientists think that neoteny may have evolved as a response to the hazards of life on land.

A few clear streams are home to an odd salamander called a Siren. (pictured at right) It is the largest salamander in the state, growing close to 12 inches in length. This animal is obligate neotenic, keeping its gills and remaining aquatic throughout life.

In-class Assignment 122:
You must be ready to make the presentation during class tomorrow receive credit.

1. Use this presentation planning guide to prepare an oral presentation about neoteny.

Day 3

What are vomerine teeth?

In-class Assignment 123:
This assignment must be turned in by the end of class today to receive credit.
Scoring criteria

1. Answer these questions about the terms on an amphibian key.
   1. What is a tympanum?
   2. Name a Texas frog that does not have a notched tongue.
   3. Explain the difference between gills and gill slits.
   4. Do only frogs have vomerine teeth?
   5. What is meant by anterior limbs?
   6. What is meant by a vertical pupil?
   7. What is a metatarsal?
   8. What is a intromittent organ?

Research Links:

Zoology Class

All tadpoles eat plant material while all frogs eat animals.
This is an advantage because it allows both adults and their offspring to live in the same area without competing for food.

Vomerine teeth are pads of wire-like teeth in the roof of the mouth.
These teeth are not used for chewing. They are used to position the prey in the mouth for swallowing.