Some basic instructions:

1. The goal of this lab is to prepare you to be able to identify amphibian species by their key characteristics, and to learn some natural history about the major groups of amphibians.  You will be tested on this material in a quiz one week from today.

2. Readings are available in labeled file folders at the side table.  DO NOT remove these folders from the  lab.

3. Be gentle with the specimens in the lab.  Always return amphibian specimens to the jar that you got them from, and DO NOT leave them out to dry – don’t return a specimen to the wrong jar!

4. A cassette tape of select amphibian calls, as well as a tape player, is available at the back of the lab.  Feel free to play the tape whenever you are working but please do not remove the tape from lab.

Exercises

1. What is an amphibian? (Read pages 3-6 in Ballinger and Lynch)

The class Amphibia is distinguished by no such simple earmark as the hair of mammals, or the feathers of birds.  For the most part amphibians have a naked skin, the young respire by means of gills and differ in body form from the adult.  There are exceptions the this characterization, for there are salamanders such as Necturus which retain the larval gills throughout life, and there are fossil amphibia, the Stegocephalia, as well as the living tropical Apoda, which have scales or plates in the skin.

    a. The following characteristics will help delineate the group:

        i. The skull articulates with the atlas by two condyles (fishes, most reptiles, and birds have a single condyle.)
        ii. The red blood corpuscles are nucleated, biconvex and oval.
        iii. Gills are present, at least during some early stages of development.
        iv. The vagus (10th) is the last cranial nerve.
        v. Development takes place without amnion and allantois.
        vi. Fins, when present, lack the supporting rays characteristic of fishes.

    b. Examine the frog skull and note the number of condyles.

    c. Study the microscope slide showing corpuscles of frog’s blood.  How are the cells different from those of a mammal?

    d. Compare specimens of a lizard and a salamander and be certain that you can tell an amphibian from a reptile.

    e. Note scales on the specimen of Apoda (caecillian).  (Do not remove it from the jar).

2. Relation of Class Amphibia to other groups of animals. (read pages 17-20 in Orr)

The amphibia are considered as intermediate between the fishes and the reptiles, but the present day examples of amphibians, which will be studied, are by no means the connecting link between the two groups.  The crossopterygian fish of the type represented by the Devonian genus Eusthenopteron was obviously on the direct line of evolution toward the early amphibians.
In upper Devonian sediments in east Greenland, fossils of primitive amphibians that are essentially intermediate between the advanced crossopterygian and early amphibians have been discovered in recent years;  they are known as ichthyostegids.  In turn, the reptiles were derived from certain labrinthodont amphibians during the Carboniferous period of earth history.

3. The Salamanders, Urodela (Caudata) (Read 3 – 12 in Bishop).

Salamanders are more abundant in humid eastern North America than any other place in the world.  There are more species in the central New York and Pennsylvania region than all of Great Britain and Europe.  They are represented in our region not only by large numbers of individuals but also by a great diversity of forms.  One of the largest families of salamanders, the Plethodontidae, is thought to have arisen in the southern Appalachians, and today they are represented in the mountains and valleys of this area by large number of species.

    a. Read pages 16 – 20 in Ballinger and Lynch

    b. Procure a specimen of an adult plethodontid salamander.  Examine the head of the specimen carefully and note the small
        groove from the nostril to the lip (use binocular microscope or hand lens).  This character alone suffices to place the
        specimen in the family Plethodontidae (pages 34 – 35 in Ballinger and Lynch).  Make a sketch of the head in anterior
        view. Note the lack of any evidence of gills, or an external ear.

    c. Observe the coastal grooves which indicate the metameric arrangement of the body muscles.  Their number is of
        importance in keying salamanders.  They should be counted high on the back including the first one close behind the
        forelimb, and the last “half”  groove specimen.  Also used by taxonomists to express the relation of the length of the limbs
        to the length of the body is the number costal folds between adpressed limbs.  How many costal folds does this specimen
        have?  How many folds between adpressed limbs?

    d. Note the condition of the toes.  An animal with five toes on both front and hind limbs is indicated in your key as 5-5.
        What is the toe formula for this species?

    e. Examine the tail of the specimens and sketch them in cross section.  Be able to distinguish rounded tails from keeled tails.

    f. Examine the specimens in lateral view and see if there is a light line from the eye to the corner of the mouth.  A light line is
        found in members of  the genus Desmognathus.

    g. Examine the roof of the mouth of the specimens at this station and, with the aid of reference plate, draw and label the
        groups of teeth.

    h. This, too is an adult salamander but observe that it has large external gills.  Examine the specimen further for the external
        characters you saw in the previous demonstration.  With what habitat would you associate the condition of the tail and the
        presence of gills throughout life?  The condition of larval features (gills, fins, etc.) present in an adult salamander is known
        as neotony.  What is paedogenesis? (see pages 28 – 29 in Ballinger and Lynch).

    i. This is the larvae of one of our local salamanders.  Note that in body form it is not unlike an adult salamander.  It has,
        however, gills, a well developed caudal fin, and a different color pattern than the adult.  Observe the various stages of
        metamorphosis in the jar. (see pages 90 – 91 in Ballinger and Lynch, read 175 – 179 in Stebbins and Cohen).

    j. An internal character used in the diagnosis of families is the presence or absence of the ypsiloid cartilage.  It is present in all
        salamandars except the sirenids, proteid, amphiumids, and plethodontids.  The ypsiliod cartilage is associated with the
        pelvic girdle and extends forward in the linea alba (midline on ventral side) from the pubis.  It furnishes attachment for
        muscles connected with respiration.  Examine the stained demonstration of this cartilage.  (Do not remove it from the
        jar).

    k. Secondary Sex Characters and Dimorphism in Urodela (Caudata). (Read pages 52 to 54 in Duellman and Trueb).

            i. Note the dark horny excresences on the rear of the hind limbs of the male of the common newt (Notophthalmus
                viridescens) during the breeding season.  These are used by the male in grasping the female during amplexus.

            ii. Examine the hedonic glands of the male two-lined salamander (Eurycea bislineata).  They form a protuberance on the
                dorsum of the base of the tail and a pad on the chin.

            iii. The four -toed salamander (Hemidactylum scutatum), shows an interesting sexual dimorphism.  Note the swollen
                condition of the nasolabial groove region, and the broadening of the head in males during the breeding season.
 

    l. Polymorphism in salamanders.

            i. Two or more types of morphs are often discovered in the plethodontids.  For example, in Plethodon cinereus there
                exists a “lead-back” type.  Examine the specimens in the jar and note these distinctive color phases.  Are there any
                other differences between the two types?

            ii. A more complicated situation exists in Desmognathus ochrophaeus where some individuals in a population which is
                sympatric with Plethodon jordani “mimic” the color pattern of P. jordani.  Examine the specimens in the jars and see
                if you can separate the Desmognathus and Plethodon.  Note the range of color variation in Desmognathus.

    m. Salamander Eggs (Read pages 162 to 170 in Stebbins and Cohen).
            i. Study and draw the egg of Ambystoma ( don’t remove from jar).  How many envelopes does the egg have?

4. The Frogs and Toads, Anura (Salientia). (Read pages 53 – 54 in Ballinger and Lynch)

The most conspicuous features of the Salientis are the pronounced change in body form from larva to adult, and enlarged powerful hind jumping legs.  Unlike the urodeles the body is compact and there is usually a conspicuous tympanum.
In the United States the Anura are most abundant in the southeast, the number of both individuals and species becoming fewer to the north.  There are, however, northern species such as the mink frog, which reach their southern limit in New York and the New England States.

    a. Examine the skeletons of frogs and toads.  Identify ARCIFEROUS and FIRMISTERNAL arrangements of the pectoral
        girdles.

    b. Be able to locate the following features on frogs;
            i. Dorsolateral fold as found in Rana pipiens.
            ii. Tympanum
            iii. Toe pads as in Hylidae

    c. Be able to locate the following features on toads;
            i. Cranial crest
            ii. Parotoid gland
            iii. Vertebral stripe
            iv. Tibial gland
            v. Metatarsal tubercle as in Scaphiopus

5. The Eggs of the Anura  (Read pages 162 to 170 in Stebbins and Cohen).

    a. The size of the adult does not determine the size of the egg.  The eggs of some of the smaller frogs like the robber frogs or
        little chorus frogs are largest while the bullfrog has relatively small eggs.

    b. In the North the egg laying season may be very short while in the South some species may breed almost any month of the
        year.  The number of eggs a female may lay varies from 6 in the robber frogs, or 100 in the little chorus frog to 10,000 or
        more in the bullfrog.

    c. Examine the different types of anuran eggs on demonstration.  Do not remove them from the jar.  Amphibian eggs are
        permanently stored (as well as preserved) in a weak formalin solution (alcohol destroys them.)
 

6. The Larvae or Tadpoles of Anurans (read pages 179-194 in Stebbins and Cohen)

    a. Examine tadpoles in the jar.  Be able to locate the following feaytures;(see pages 91–93 in Ballinger and Lynch)
            i. lateral lines
            ii. breathing pore or spiracle,
            iii. labium (oral disc)

    b. Determine the genus of the two tadpoles in demonstration by means of the mouthparts with the aid of the key in Ballinger
        and Lynch.

7. Sexual Dimorphism in the Salientia. (Read pages 54-60 in Duellman and Trueb).  Examine the following features:

    a. nuptial pads on the inner surface of the thumb.  What is the function of this pad?.

    b. extended toe webbing as found in the male wood frog (Rana sylvatica)

    c. large tympani found in the male bullfrog and green frog.

8. Vernal Ponds: Important Amphibian Habitats (Read article by Cassell – a former Vert Zool student).

9. Declining Amphibians (Read page 210, 241-247 in Stebbins and Cohen)