Stages in the Development of Toads

Stages in the Development of Toads

Toads and frogs have many differences, but they share a similar life cycle as amphibians. Both of them live part of their lives in water and part on land.

During the rainy season, male and female toads start looking for each other to mate. This is called courtship. The male toads make loud croaking sounds to attract females that are swollen with eggs.

This process continues with the male and female toads laying and fertilizing eggs. The development of a young toad involves various stages.

At first, the small toad has a tail and breathes like a fish. Initially, the young toad has a tail and uses external gills for breathing. This means it uses small feathery parts on its neck to take in air from water.

Later, it loses its tail, grows legs, and develops lungs instead of gills. At each stage of development, the toad is given a different name.

Spawn

The mother toad goes back to the water when it is time to have babies. The female toad returns to a river or stream during the breeding season.

The father toad holds her tight while she lays her eggs. There, the male toad finds her and jumps on her back in a process called amplexus. This is just a fancy name for the way they hold each other during mating.

He wraps his legs around her while she lays her eggs in a long chain. As she lays the eggs, he fertilizes them.

All the eggs laid together in a big group are called spawn. The group of fertilized eggs is called spawn. This term refers to the collective mass of eggs rather than each egg developing independently.

The eggs are covered in a slippery jelly that looks like long strings. The eggs are encased in jelly strings, which serve several important purposes. These jelly strings protect the eggs from mechanical damage, prevent them from drying out, ensure they have access to oxygen, and protect against microbial attacks.

Fertilized Egg

After the male and female parts join, the egg starts growing by dividing its cells. After fertilization, the zygote undergoes mitotic cell division to develop into an embryo. This means one cell splits into many to build the baby toad.

The food inside the egg, called the yolk, divides into two parts, then four parts. This splitting process continues, causing the yolk to resemble raspberries inside a jelly cup.

As the baby grows, it starts to look like a tiny fish with a tail. As development progresses, the embryo begins to take on the shape of a tadpole and grows longer.

If you look very closely at the jelly, you can see the baby moving inside. If observed closely, you can see the embryo swimming within the egg.

The baby eats the food stored in the egg and breathes through the jelly. The embryo obtains its nutrients from the yolk and dissolved oxygen through the jelly.

Tadpole

The eggs open up and the babies come out after about one to three weeks. The eggs begin to hatch between 6 to 21 days after fertilization, depending on the type of toad and environmental factors.

When it comes out, the tadpole uses a sticky part under its head to hang onto water plants. When it hatches, the tadpole attaches itself to a water weed using a sticky substance secreted by a gland located under its head.

The tadpole does not have a mouth yet, so it lives on the food left in its stomach. Initially, the tadpole feeds on the egg yolk, as it does not yet have a mouth, and absorbs oxygen through its skin.

The very young tadpole has a head, body, and tail, with three feathery gills on the outside of its neck. In the early stages, the young tadpole has a head, body, and tail, with three external gills on either side of its head.

It grows hard jaws so it can eat green plants in the water. It develops horny jaws for feeding on water weeds.

The stomach of the tadpole is long and coiled like a spring, and the sticky gland is still there. The intestine is long and coiled, and the cement gland is still present.

The tadpole breathes with gills that you can see on the outside of its body. The tadpole breathes through its external gills, which are visible from the outside.

As it grows, the outside gills disappear and new gills grow inside its body. As it grows, the external gills disintegrate, and internal gills develop.

A skin cover grows over the gills so the tadpole can breathe just like a fish. A gill cover, called the operculum, grows over the gills, allowing the tadpole to breathe like a fish.

The tadpole’s tail gets longer and stronger. The tadpole’s tail elongates, and muscle development occurs.

For the first few days, the tadpole just stays near the plants and does not swim around much. For the first 7 to 10 days, the tadpole floats among the plants as it continues to grow without swimming.

The back legs grow first, and then the front legs grow later. The hind limbs develop first, followed by the forelimbs.

The front leg on the left side comes out first, then the right one follows. The left forelimb appears first through the opercular opening, and then the right forelimb follows.

The gills inside start to go away as the lungs for breathing air start to form. The internal gills gradually break down, while the lungs start to develop.

A real mouth grows to replace the hard jaws, and the stomach gets shorter because it now eats small water animals. The mouth forms to replace the horny jaws, and the intestine shortens as the tadpole begins eating small animals in the water.

Its eyes also grow larger and stand out more on its head.

Youth and Adulthood

Finally, the tail disappears into the body and the tadpole becomes a tiny toad. Eventually, the tadpole reabsorbs its tail and transforms into a small toad. This means the tail is not cut off, but the body drinks it back in.

It leaves the water to live on dry land and grow into a big toad. It emerges from the water and lives on land as it continues to grow into a full adult toad.

When it is fully grown, it will go back to the water to have its own babies. After reaching adulthood, it will return to the water to mate and fertilize more eggs.

Until then, the adult toad stays away from water and eats insects like ants and flies. The entire change from egg to adult takes about 40 to 45 days.

This big change in the toad's body is controlled by a special chemical in the body. This transformation is regulated by the hormone thyroxine, which is produced by the thyroid gland located between the head and trunk.

Role of Hormones in Development of Toad

A special body chemical called thyroxine controls how the tadpole changes into a toad. In toads and other amphibians, metamorphosis is controlled by the hormone called thyroxine. This chemical tells the body when to grow legs and lose the tail.

This hormone is made by the thyroid glands found where the head joins the body.

The water must have a mineral called iodine for the toad to make this chemical. For thyroxine to be created, iodine must be present in the water.

If this chemical is not there, the tadpole will never become a toad. Without this hormone, the tadpole cannot develop into an adult form.

If there is plenty of this chemical, the tadpole will change into a toad very quickly. However, an increase in thyroxine levels speeds up the process of metamorphosis.