How do tadpoles become frogs? - The metamorphosis of frogs

Frogs have a very unique growth process. They undergo a process called metamorphosis, gradually developing from aquatic tadpoles to adult frogs that can live on land. In this process, frogs undergo huge changes in morphology, physiology, and lifestyle. This article will detail how tadpoles gradually become frogs, and analyze the physiological changes and environmental adaptability involved in this process.

1. The life cycle of a frog

The life of a frog can be divided into four main stages:

1. Eggs

2. Tadpole

3. Frog

4. Adult Frog

Each stage is accompanied by obvious changes in body structure and physiological functions.

2. Main stages of metamorphosis

(1) Egg stage: the starting point of life

• Frog fertilization method: Frogs undergo external fertilization in water, females lay hundreds to thousands of eggs, and males release sperm in the water for fertilization.

• Egg characteristics:

• The diameter is about 1-3 mm, and it is covered with a transparent gelatinous membrane that helps keep it moist and provides protection.

• Hatching takes about 7-10 days after fertilization. The hatching speed is affected by water temperature, and hatching is faster in warm waters.

(2) Tadpole stage: small life in the water (1-8 weeks after hatching)

After hatching, tadpoles are completely different from adult frogs. They are more like fish and are specially adapted to the aquatic environment.

Main characteristics of tadpoles:

• Appearance: small, round body with a long tail for swimming.

• Breathing method: Initially, they rely on external gills to breathe, and then they grow internal gills, similar to the breathing method of fish.

• Movement method: They rely on tail swinging to swim in the water, and their limbs have not yet developed.

• Diet: Initially, they are herbivorous, feeding on algae and plankton in the water.

In the early stages of tadpoles, they rely almost entirely on nutrients and food in the water to grow until they enter the next stage of metamorphosis.

(3) Late growth: limbs begin to appear (5-8 weeks)

At about 5-8 weeks, the tadpole's body begins to undergo significant changes, and they gradually transition to the morphology of a young frog.

Main changes:

1. Hint limbs grow first:

• About 5 weeks later, the tadpole's hind legs begin to grow from both sides of the body.

• The hind legs develop earlier than the front legs because they are the main source of power for frogs to jump.

2. Forelimbs appear:

• At about 7-8 weeks, the forelimbs develop in the gill cavity and then break through the gills to expose.

• At this time, the tadpole's shape is close to that of a young frog.

3. The tail gradually shortens:

• The nutrients in the tail are reabsorbed and converted into energy needed for body growth.

• Adult frogs do not need tails, so the tail will eventually disappear completely.

4. Changes in the respiratory system:

• The original gills gradually degenerate, and the lungs begin to develop. The young frogs can float to the surface of the water and breathe air with their lungs.

• This change means that frogs gradually adapt from a completely aquatic life to an amphibious life.

(4) Young frog stage: about to complete metamorphosis (9-12 weeks)

As the limbs are fully grown and the tail basically disappears, the tadpole becomes a young frog and can leave the water for a short time and try to move on land.

Characteristics of young frogs:

• Small in size, similar in appearance to adult frogs, but slightly clumsy in proportion.

• Respiration mainly relies on lungs, but can still be assisted by skin.

• Changes in diet: From herbivorous to carnivorous, it begins to prey on small insects, mosquito larvae, etc.

• Start jumping: The hind limbs are well developed, and it gradually learns to move by jumping instead of relying solely on swimming.

(5) Adult frog stage: fully terrestrial amphibian (after 12 weeks)

After about 12-16 weeks of growth, the young frogs become adult frogs and can move freely between land and water.

Characteristics of adult frogs:

• Strong limbs, well-developed hind limb muscles, capable of long-distance jumping.

• Fully lung breathing, but can still absorb oxygen through the skin, especially underwater.

• Completely carnivorous, with insects, earthworms, spiders, and small invertebrates as their main food.

• Reproductive capacity: Adult frogs return to the water to mate and lay eggs, completing the life cycle cycle.

3. Scientific significance of frog metamorphosis

The metamorphosis process of frogs is one of the most typical biological development patterns in nature, which shows the transformation from aquatic to terrestrial.The evolutionary adaptation of, its significance includes:

(1) Ecological adaptation

• Tadpoles live in water, and frogs can adapt to land and water. This evolutionary method reduces the food competition between different stages.

• The larvae (tadpoles) and adults (frogs) feed differently, avoiding food competition among the same species and improving survival rate.

(2) Environmental adaptability

• The metamorphosis process of frogs depends on temperature, humidity and food supply, and environmental changes will affect their development speed.

• Due to climate change and habitat destruction, the number of frogs is decreasing in some parts of the world.

(3) Scientific research

• **Hormonal changes (such as thyroxine) during frog metamorphosis are of great value to animal physiology research.

• The developmental pattern of tadpoles is used in the study of biological evolution, ecology and developmental biology.

4. Conclusion

The process of tadpoles turning into frogs is a typical metamorphosis, which goes through four main stages: egg, tadpole, young frog, and adult frog.

1. The eggs hatch into tadpoles, which initially have no limbs and breathe only through gills, and are completely aquatic.

2. The tadpoles gradually grow hind legs and front legs, their respiratory system transitions from gills to lungs, and their tails gradually disappear.

3. The young frogs transform into adult frogs, fully adapting to the terrestrial environment and beginning to feed on insects.

This process demonstrates the wonderful changes in organisms in environmental adaptation, survival strategies and evolution, and is a classic case in biological research.

animal tags： frog