In frogs and insects hormones play an important role in metamorphosis. The hormone thyroxine is helpful in metamorphosis of frog i.e conversion of tadpole to frog. The ecdysone and Juvenile hormone (JH) helps in metamorphosis of insects i.e conversion of pupa to adult form.

Role of Hormones in Completing the Life History of Insects and Frogs

Hormones play a crucial role in the development and completion of the life history of both insects and frogs. These small chemical messengers are produced by specialized glands and are responsible for regulating various physiological processes within the organisms. In insects and frogs, hormones control growth, metamorphosis, reproduction, and many other essential functions.

Role of Hormones in Insects:
In insects, hormones known as ecdysteroids and juvenile hormones are primarily involved in their life history.

1. Ecdysteroids: Ecdysteroids are responsible for regulating molting and metamorphosis in insects. They control the process of shedding the old exoskeleton and growing a new one during molting. Ecdysteroids are produced by the prothoracic glands and stimulate the synthesis of new cuticle layers. They initiate molting by activating enzymes that break down the old cuticle and trigger the formation of a new one.

2. Juvenile Hormones (JH): Juvenile hormones are involved in regulating the transition between larval stages and metamorphosis in insects. They are produced by the corpora allata glands and promote the maintenance of larval characteristics while inhibiting the development of adult features. As the levels of juvenile hormones decrease, the insect undergoes metamorphosis and transforms into the adult form.

Role of Hormones in Frogs:
In frogs, hormones such as thyroxine and gonadotropins play vital roles in their life history.

1. Thyroxine: Thyroxine is a hormone produced by the thyroid glands in frogs. It is responsible for regulating the rate of metabolism and growth during different stages of development. In tadpoles, thyroxine stimulates the growth of tissues, particularly the hind limbs and lungs. As the tadpole undergoes metamorphosis, the levels of thyroxine increase, triggering the transformation into an adult frog.

2. Gonadotropins: Gonadotropins are hormones secreted by the pituitary gland in frogs. They control the development of the reproductive system and the production of gametes. Gonadotropins stimulate the maturation of the gonads (testes in males and ovaries in females), leading to the production of sperm or eggs. They also regulate the release of sex hormones, such as estrogen and testosterone, which are essential for reproduction.

Overall, hormones play a crucial role in coordinating and regulating the complex life history of insects and frogs. They control growth, development, metamorphosis, and reproductive processes, ensuring the successful completion of their life cycles.

The thyroid gland secretes thyroxine (TH), a hormone essential for the growth and development of all vertebrates including humans. To understand TH action, the Donald Brown lab studies one of the most dramatic roles of the hormone, the control of amphibian metamorphosis—the process by which a tadpole turns into a frog. He studies the frog Xenopus laevis, from South Africa, because it is easy to rear. Events as different as the formation of limbs, the remodeling of organs, and the resorption of tadpole tissues such as the tail are all directed by TH. How can a simple molecule control so many different developmental changes? The hormone works by regulating the expression of groups of genes. It instructs some genes to absorb the tail and gills and others to start new tissues and organs.

The lab has developed a strategy to analyze this complex programing. They have identified genes that are regulated by TH in a variety of tissues and organs by hybridizing probes with micro arrays prepared by Agilent Technologies.