Lab 3: Amphibian Info

Question 1

herpetology

Answer 1

“Class Amphibia” and “Class Reptilia” were traditionally studied together by the discipline called herpetology.

Along with fishes, both groups were considered among the “lower” vertebrates and together they represented the ectothermal tetrapods.

Increased knowledge of the evolutionary history of vertebrates has shown that living amphibians and reptiles are not closely related to each other.

Question 2

I. Survey of the Amphibians

A. Evolution of the first tetrapods and the amphibians

1. Tetrapods evolved from sarcoterygians

Answer 2

1. Tetrapods evolved from Sarcopterygian (lobe-finned) fishes in the Late Devonian (370 million years ago). The crocodile-like panderichthyids are currently thought to be the closest fish-like relatives of tetrapods.

a. Panderichthyids were large carnivorous fishes of shallow water habitats of the late Devonian. Panderichthyids and other lobe-finned fishes possessed lungs; some had choanae, well-ossified skeletons, and fins supported by bones similar to tetrapod limbs.

b. Fossils of early tetrapods are known from fresh and brackish water deposits. Recent discoveries suggest that, at least as adults, many of the first tetrapods were more aquatic than previously realized. Some species even had fish-like internal gills. The relatively well-known Ichthyostegidae had caudal fins, scales, and vertebral columns very similar to those of lobe-finned fishes and as many as eight digits on the limbs.

Question 3

I. Survey of the Amphibians

A. Evolution of the first tetrapods and the amphibians

2. Only three groups now

Answer 3

Only three groups now remain from early radiation of tetrapods. These animals can properly be termed “Amphibians”, although the name is no longer applied to the many other, extinct lineages of non-amniote tetrapods.

a. Order Caudata (salamanders)
b. Order Anura (frogs and toads)
c. Order Gymnophiona (legless amphibians or caecilians)

These groups first appear in the fossil record of the Mesozoic. Anurans (frogs and toads) and Caudates (salamanders) are more closely related to one another than to the Gymnophionians (caecilians).

Question 4

Why life on land?

Answer 4

There are several theories, three of these theories are:

a. Vast terrestrial niche available, competition and predation were severe in aquatic habitats so being partially terrestrial was highly advantageous.

b. Terrestrial adaptations increased the survival as aquatic animals rather than as terrestrial animals. Reasoning - Devonian was a time of great climatic fluctuations. Environments were stagnant or overcrowded; survival was enhanced if an animal was able to reach larger bodies of water by crossing over land.

c. They were highly successful predators searching for new prey (terrestrial invertebrates).

Question 5

Integumentary Adaptations

Gas exchange and water conservation

Answer 5

Several integumentary features of living amphibians are related to gas exchange through the skin and to water conservation

Question 6

Integumentary Adaptations

Adaptations of the epidermis:

Answer 6

a. Warts.
b. Keratinized epidermal claws.
c. Keratinized teeth in some larvae for feeding.

Question 7

Integumentary Adaptations

Specialized glands derived from the epidermis

a. Mucous glands

Answer 7

produce protective mucous, poisons and pheromones.

Mucous glands produce a thin layer of mucus that keeps the outer layer of skin moist and facilitates gaseous exchange. Mucus secretions can also serve as a protective mechanism by making the animal slippery and difficult to capture.

Question 8

Integumentary Adaptations

Specialized glands derived from the epidermis

b. Poison glands

Answer 8

Poison glands are concentrated in strategic areas, e.g., parotoid glands behind the head in some toads and frogs, or along the backs of some salamanders.

Poisonous secretions of amphibians are usually milky in texture.

Some secretions contain alkaloid substances which resemble digitalis in action (increases tonicity of heart, weakens respiration, causes paralysis and varying degrees of nausea)

Question 9

Integumentary Adaptations

Specialized glands derived from the epidermis

c. Hedonic glands

Answer 9

Hedonic glands are glands whose primary function is to stimulate sexual interest by releasing pheromone secretions.

Question 10

Integumentary Adaptations

Colour

Answer 10

Amphibians offer many outstanding examples of anti-predation coloration, particularly the use of camouflage and aposematic coloration. Appendix B, Adaptive Coloration, defines these and other uses of color seen in amphibians.

Question 11

Integumentary Adaptations

Breeding

Answer 11

Accessory breeding structures, e.g., nuptial pads.

Question 12

Water Relations

Answer 12

Extant amphibians have a glandular skin, without external scales, that is highly permeable to water. Water and gases are readily permeable, although other compounds (e.g. sodium) are regulated.

They have little ability to control the loss of water from the body via physiological or structural means when they are on land. Therefore, amphibians are adapted to live in environments that are rich in water but poor in salts. These physiological limitations have shaped the worldwide distribution of amphibians. They are most diverse and abundant in moist habitats. They are rare on oceanic islands.

Question 13

Communication

Answer 13

1. Visual communication is well developed in some species of salamanders where males
   and females perform complex courtship “dances” before mating.
2. Audible communication is critical for reproduction in most anurans. Calls convey information regarding the species, sex, size and condition of the caller and the location of breeding sites. Males and females possess a laryngeal apparatus for sound production; males also have a vocal sac, a ventral extension of the mouth cavity that acts as a resonating chamber.
3. Amphibians employ chemical communication in a variety of situations. Examples include use of chemical secretions from glands on the head and tail to coordinate courtship by salamanders and the use of olfaction to recognize kin in schooling anuran tadpoles.

Question 14

Metamorphosis and Development

Metamorphosis

Answer 14

Amphibian metamorphosis is defined as a series of abrupt postembryonic changes involving structural, physiological, biochemical, and behavioural transformations.

Hormones ultimately control all events of larval growth and metamorphosis.

The thyroid gland (developmentally related to the endostyle) is the keystone of amphibian metamorphosis.

The changes of metamorphosis are stimulated by actions of the hormone thyroxine (from the thyroid gland).

The effects of thyroxine vary around the developing tadpole’s body.

For example, thyroxine administered to a tadpole’s developing leg stimulated its growth; applied to a tadpole’s tail, thyroxine breaks down the tissue.

Question 15

Metamorphosis and Development

Paedomorphosis

Answer 15

Paedomorphosis is the retention of ancestral juvenile characters in later developmental stages of descendants. In its most extreme form, paedomorphosis results in the attainment of sexual maturity by an animal that retains a larval body form for its entire life (i.e., never completes metamorphosis). Paedomorphosis may be accomplished via two different processes:

Question 16

Metamorphosis and Development

Paedomorphosis

A. Neoteny

Answer 16

Neoteny – retention of one or more larval or embryonic traits in an otherwise adult body. This involves the slowing down or stopping of development of the traits affected. Occurs in many groups of amphibians, including the Family Ambystomidae, several species of plethodontid salamanders, a few anuran species and the families Salamandridae and Hynobiidae.

Question 17

Metamorphosis and Development

Paedomorphosis

B. Progenesis

Answer 17

Progenesis -early development of the gonads in a morphologically juvenile stage. This involves the speeding up of the development of the reproductive system. Several examples are found in the families Sirenidae, Amphiumidae, Cryptobranchiae, and Proteidae.

Question 18

Amphibian Reproduction and Development

Answer 18

1. Amphibians require either moist environments or bodies of water for breeding.
2. Environmental factors affecting breeding cycles:

a. Photoperiod.
b. Temperature.
c. Precipitation.
d. Abundance of food.

Each factor may affect a given group of amphibians in different ways, depending on the species and habitat.

Question 19

Amphibian Reproduction and Development

Female and male reproductive systems

Answer 19

The gonads of amphibians are sexually indifferent initially.

Their development into either testes or ovaries is affected by hormones, including artificially created androgen (female hormone) molecules in plastics and in human contraceptives; it can also be affected by changes in temperature.

If the growth of the gonad features more development of the cortex than the medulla, the germ cells become oocytes, and mature into eggs.

If there is greater growth in the medulla, the germ cells migrate into it and become spermatocytes and mature into sperm.

Question 20

Amphibian Reproduction and Development

Female and male reproductive systems

Ovaries are __

Answer 20

sac-like and their shape tends to parallel that of the kidney.

i. The eggs within are at different stages of maturity.
ii. The number of eggs released during ovulation varies from a single egg to
many thousands.

Question 21

Amphibian Reproduction and Development

Female and male reproductive systems

Testes are __

Answer 21

connected to the anterior of the kidney and are composed of the seminiferous tubules. The tubules include spermatogonia, which mature into sperm.

i. Testes are also endocrine glands and produce testosterone.
ii. Fat bodies are associated with the testes (and ovaries) and appear to function as an energy source for gonadal activity.

Question 22

Amphibian Reproduction and Development

Sexual Dimorphism

Answer 22

a. Some species of anurans show conspicuous differences between the sexes. In other species it may be difficult to separate the male and female by external features.

b. The males of some species may show external vocal sacs. These are found on the floor of the mouth and extend outward when inflated. These serve as resonators to reinforce sounds made by the normal vocal cords within the laryngeal region.

c. During the breeding season many males develop pigmented callosities known as nuptial pads. Nuptial pads are dark, usually roughened areas on the hands and other regions of male frogs. Those on the hands assist in gripping the female during amplexus. There are associated with the breeding cycle and disappear when the animals are sexually inactive.

d. Male tailed frogs (Ascaphus truei) possess a copulatory organ.

Question 23

Amphibian Reproduction and Development

Parental Care and Number of Eggs.

Answer 23

In general, there is a correlation between the number of eggs laid and the mortality suffered by the species prior to sexual maturity. The number of eggs is also influenced by:

a. Size of eggs.
b. Pattern of development (direct or indirect).
c. Size of female.
d. Reproductive behaviors.
e. Internal or external development

Question 24

Amphibian Reproduction and Development

Reproductive Variety

A. Caecilians

Answer 24

i. Most members of this group have internal fertilization. This is accomplished by a male intromittent organ that is protruded from the cloaca.

ii. Some caecilians lay eggs, but ovoviviparity is widespread (eggs are retained in oviducts and the female gives birth to live young – young get nourishment from the yolk of the egg).

iii. Many caecilians are viviparous. The fetuses may initially utilize egg yolk for nourishment but this quickly runs out. The young fetuses are then dependent on their mother for nourishment. It appears that the fetuses obtain energy by scraping material from the walls of the oviduct with specialized embryonic teeth. This scraping stimulated the oviduct to secrete a thick, white, creamy substance that has been called uterine milk. Their diet consists of uterine milk and epithelial cells from the oviduct (which are quickly regenerated by the mother).

Question 25

Amphibian Reproduction and Development

Reproductive Variety

B. Salamanders

Answer 25

i. Most salamanders utilize internal fertilization but there are a few that retain external fertilization.

ii. Internal fertilization is often accomplished not by an intromittent organ but rather by the transfer of a packet of sperm (the spermatophore) from male to female.

iii. Salamanders have elaborate patterns of courtship. Courtship patterns are important species-isolating mechanisms and they show great variation. Generally the courtship is initiated by the male with the ultimate goal that the female will pick up the spermatophore with her cloacal lips.

iv. In most cases, salamanders that breed in water lay their eggs in water. The eggs hatch into gilled aquatic larva which, except in paedomorphic forms, transform into terrestrial adults.

v. There are a number of species that have dispensed with the aquatic larval stage and live an entirely terrestrial existence.

vi. A few salamanders give birth to live larva which are released in water and later transform into a terrestrial adult.

vii. Some salamanders adopt various life history patterns within the same species. Larval salamanders (i.e., tiger salamanders) may metamorphose into terrestrial adults or undergo paedomorphosis and remain a reproductively mature aquatic larva. Environmental conditions and genetic predisposition determine which route an individual may take.

Question 26

Amphibian Reproduction and Development

Reproductive Variety

C. Frogs

Answer 26

i. Frogs and toads are well known for their vocalization called advertisement calls.

ii. Advertisement calls serve to identify the species and sex of the caller. Among territorial anurans the calls may also serve for individual recognition and allow other frogs to “size” up the competition or presence of individuals (pitch of call varies with body size).

iii. Fertilization is external for most anurans (exceptions include frogs that lay eggs on land and for those few species that are live-bearers).

iv. Fertilization is accomplished by amplexus (a “sexual embrace”) where the male uses his forelegs to grasp the female in order to deposit sperm on the eggs as the female lays them.

v. The primitive pattern of anuran reproduction is to lay a large number of small eggs in hopes that the law of averages allows a few to survive to maturity. Such large clutches may require up to 50% of the energy reserves of the individual.

vi. Some anurans lay fewer eggs, that are larger and use the extra energy to protect the eggs from predation:
- Lay eggs on leaves out of water, tadpoles hatch and drop into water.
- Construct foam nests that float on water.
- Egg holding (hold eggs on body until they hatch).
- Tadpole guarding, brooding or holding.