Hormones are the chemical messengers that carry out essential activities in various life forms like plants, animals and human beings. Hormones play a very crucial role in the life history of insects and frogs. These are required in less quantity, but insects and frogs’ life cycle gets hindered without them. Let us know more about the Role of Hormones in Completing the Life History of Insects and Frogs.

Hormones have a crucial part in the metamorphosis of frogs and insects. The hormone thyroxine aids in frog metamorphosis or the transformation of a tadpole into a frog. Ecdysone and juvenile hormone (JH) aid in insect metamorphosis, or the transition from pupa to adult form. Continue reading this article to know more about how Hormones help in Completing the Life History of Insects and Frogs.

What is Metamorphosis?

Metamorphosis is the biological process that results in the change in morphological attributes in an animal. It occurs after birth or hatching during the development cycle. Metamorphosis is the characteristic feature of insects like a butterfly, silkmoth, house fly, mosquito, etc., and amphibians like frogs, toads, etc.

Types of Metamorphosis

Based on the degree of changes, the metamorphosis found in insects is five different types. They are given below:
1. Ametabolous development or Direct development
2. Gradual meta­morphosis or Paurometabolous develop­ment
3. Incomplete metamorphosis or Hemimetabolous development
4. Complete metamorphosis or Holometabolous development
5. Hypermetamorphosis or Hypermetabolous development

1. Ametabolous development or direct development: In this type, the insects undergo little or no metamorphosis. The young ones look like adults in all respects except in size and sexual characters. This development is found in apterygota (wingless) insects like silverfish, springtails, etc.

Fig: Ametabolous Development in Silverfish

2. Gradual meta­morphosis or Paurometabolous develop­ment: In this type, the young ones or nymphs undergo a periodic development of various morphological characters like reproductive organs, wings, etc. Here the nymph undergoes a slow but steady change in each moult and attains the adult form. This is found in cockroaches, grasshoppers, mantis, white ants, etc.

Fig: Paurometabolous develop­ment

3. Incomplete metamorphosis or Hemimetabolous development: In this type, the insects resemble a life cycle similar to paurometabolous development where the nymph forms called naiads attain adult forms by gradual morphological change with each successive moults. Naiads are aquatic, but the adult form is terrestrial. Naiads respire by external gills, while the adults develop various respiratory structures to be adapted to terrestrial life cycle. This is found in dragonflies, mayflies, and damselflies.

Fig: Hemimetabolous development

4. Complete metamorphosis or Holometabolous development: In this type, rapid morphological change takes place during post-embryonic transformation. In some forms of insects, the larva shows no similarity with the adult, and there is always a pupal stage. In this type, insect development occurs in four stages: egg, larva, pupa, and adult. This is found in beetles, caddisflies, butterflies, moths, mosquitoes, flies, bees and wasps. 

Fig: Complete Metamorphosis

5. Hypermetamorphosis or Hypermetabolous development: In this metamorphosis, two or three specific types of larval instars with different habits and structures are present in certain insects. This is found in blister beetles.

Fig: Hypermetabolous Development

Life Cycle of Frog

A frog is an amphibian that lives both in water as well as on land. It shows both progressive and retrogressive metamorphosis during its development. The life cycle of a frog is described below:
(a) The life cycle of a frog starts from fertilized eggs. The eggs are released by female frogs during copulation and fertilization of such eggs occur in water. 
(b) The larvae or tadpoles hatch out from the fertilized egg and grow in size.
(c) The tadpole lives in water. The tadpole looks very different from the adult frog, and it looks like a fish.
(d) The tadpole has no legs and breathes through gills. It uses a long tail to swim.
(e) Then the tadpole grows into a froglet. It has legs for walking and hopping. It also contains lungs for breathing air.
(f) The adult frog is formed from the froglet. It lives both on land and water. It has webbed feet for swimming and also for hopping on land. It can breathe through the lungs and also through thin, moist skin.

Fig: Lifecycle of a Frog

Role of Hormones in the Life History of Insects

The process of metamorphosis in insects requires some hormones; these are known as insect moulting or metamorphosis hormones. The ecdysone hormone is secreted from the prothoracic gland and the Juvenile hormone (JH) is secreted from corpora allata. The primary role of the Juvenile hormone in insect development is to modulate the action of ecdysone, and also plays a vital role in development, polyphenism, i.e. development of different traits under different climatic conditions, reproduction, and behaviour throughout insect life. Ecdysone produces both pre-differentiated and differentiative cellular events but regulates both early development and late development genes that are required for the molting and metamorphosis to occur. Thus the presence of JH and ecdysone develops a molt to a larval stage. If both these hormones are absent at the onset of the molt, metamorphosis will not occur.

Role of Hormones in the Life History of Frogs

The metamorphosis in frogs, i.e. the transformation of a tadpole into an adult frog, is controlled by the action of thyroxine hormones. Thyroxine hormone is produced from the thyroid gland.  If the thyroid gland is removed from a tadpole it will not develop into an adult frog. The production and synthesis of thyroxine hormone required a mineral known as iodine. The tadpole can only get iodine from the water. The tadpole in water that does not contain iodine will not develop into an adult frog, and hence the metamorphosis will not occur.

Summary

Metamorphosis is the biological process that occurs in an animal’s body physically after birth or hatching during the development cycle. Metamorphosis is the characteristic feature of insects like a butterfly, silkmoth, house fly, mosquito, etc., and amphibians like frogs, toads, etc. The metamorphosis found in insects direct development, gradual meta­morphosis, incomplete metamorphosis, complete metamorphosis and hypermetamorphosis. The amphibians metamorphosis are progressive metamorphosis and retrogressive metamorphosis. The ecdysone and Juvenile hormone (JH) helps in the metamorphosis of insects, and the thyroxine hormone helps in the metamorphosis of frogs.

Frequently Asked Questions

We have provided some frequently asked questions on Hormones in Completing the Life History of Insects and Frogs here:

Q.1. Which hormone controls the metamorphosis in frogs?
Ans: Thyroxine hormone controls the metamorphosis in frogs.

Q.2. What do you mean by complete metamorphosis?
Ans: In this type, rapid morphological change takes place during post-embryonic transformation. In some forms of insects, the larva shows no similarity with the adult, and there is always a pupal stage.

Q.3. What is metamorphism?
Ans: Metamorphosis is the biological process that occurs in an animal’s body physically after birth or hatching during the development cycle.

Q.4. What are the main hormones involved in insect metamorphosis?
Ans: The main hormones involved in insect metamorphosis are ecdysone and juvenile hormones.

Q.5. What are examples of metamorphosis?
Ans: The examples of metamorphosis are insects and amphibians.

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