Metamorphosis is the phenomenon of dramatic developmental changes in which an immature organism turns into a sexually mature form. In this process, large proportions of structural changes occur in such a way that its younger form and older form are unrecognizable. These changes are initiated by endocrine factors and few hormones that will possibly affect every cell in the developing body.
Metamorphosis can be said as both developmental and an ecological conversion–
- Developmental– Metamorphosis is initiated by specific hormones that reactivate the developmental process whereby it is adjusting itself morphologically, physiologically and behaviorally.
- Ecological– This sort of evolution is associated with fluctuations in habitat, food and behavior.
Metamorphosis can be categorized in 2 types on the basis of formation: Complete and Incomplete metamorphosis-
Complete metamorphosis-It is a type of insect development in which egg, larva, pupal and adult stages differ among them greatly during the process of metamorphosis. The four stages that can be categorized are- Egg, larva, pupa and adult. Here, the metabolically active form is larvae and the inactive one is the pupa. The exoskeleton, particularly of the insect is completely molted. Sexually active is the final stage of the insect (adult). Examples of this type include Wasps, ants and fleas.
Incomplete metamorphosis-It is a type of insect development where gradual changes occur in the insect during the development from egg to adult. The three stages categorized are- Egg, nymph and adult. The nymph can be identified as a miniature adult. Certain portions of exoskeleton in the adults remain permanent throughout its life. Sexually active is the former stage of the insect. Examples of this type include termites, mantis and cockroach.
On the basis of the mode of developing, it is divided as: Direct and Indirect developers
Direct developers– Those organisms whose young structurally mimic the adult’s structure and are sexually inactive. Example- Humans.
Indirect developers– Those organisms which includes a larval stage with characteristics and features very different from those of adult organism. They can further be classified as primary and secondary larvae.
- Primary larvae represent different body plans than adult one and are structurally very distinct. Example is sea urchin.
- Secondary larvae are those larvae which are also the adults which possess basic body plan. Example is Butterfly.
Heterochrony– It is the phenomenon whereby there is a genetically controlled time difference in the rate of development process in an organism compared to its ancestors, therefore, showcasing a marvelous morphological innovation. The notion “heterochrony” was first introduced by the German zoologist Ernst Haeckel in 1875 for which he mainly used it explain the rare conditions of “recapitulation theory” (a hypothesis where a developing embryo, when going through all walks of life resembles the adult form of distinct ancestors.) For now, we will ponder over pedomorphosis’s subtypes.
PAEDOMORPHOSIS:
* Progenesis– It involves the retention of juvenile form, but in this case, the gonads and germ cells develop at a faster rate than normal. This becomes sexually mature while the rest of the body is still in a juvenile phase.
* Neotony– It refers to the retention of the juvenile form owing to the retardation of body development relative to that of the germ cells and gonads, which achieve maturity at the normal time.
* Direct development– Here, the embryo skips the larval step and proceeds with the creation of adult stage.
PERAMORPHOSIS:
* Hypermorphosis- During the course of evolution, the rate of development is unchanged but the relative time duration is increased, thereby allowing the addition of new stages to the end of the ancestral categorization process.
* Acceleration- The essential developmental changes, but in a shorter time (varying growth rates).
* Predisplacement- A modification in the ontogeny of a successor such that some developmental process begins earlier than in its ancestor.
BY- N. Shreya Mohan (MSIWM042)
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