Everything about Metamorphose totally explained
Metamorphosis is a
biological process by which an
animal physically
develops after
birth or hatching, involving a conspicuous and relatively abrupt change in the animal's form or structure through cell
growth and
differentiation. Some
insects,
amphibians,
molluscs,
crustaceans,
cnidarians,
echinoderms and
tunicates undergo metamorphosis, which is usually (but not always) accompanied by a change of
habitat or
behaviour.
Scientific usage of the term is exclusive, and isn't applied to general aspects of
cell growth, including rapid
growth spurts. References to "metamorphosis" in
mammals are imprecise and only colloquial.
Etymology
The word "metamorphosis" derives from
Greek μεταμόρφωσις, "transformation, transforming", from
μετα- (
meta-), "change" +
μορφή (
morfe) "form".
Insect metamorphosis
Comparative Lengths of Metamorphosis>
| Species |
Egg |
Larva/Nymph |
Pupa |
Adult |
| Housefly |
1 day |
2 weeks |
1 week |
2 weeks |
| Ladybird |
4 days |
2 weeks |
2 weeks |
3-9 months |
| Monarch Butterfly |
4 days |
2 weeks |
10 days |
2-6 weeks |
| Periodical Cicada |
1 month |
13/17 years |
no such stage |
2 months |
| Mayfly |
1 month |
3 years |
1 day |
| Cockroach |
1 month |
3 months |
9 months |
Metamorphosis usually proceeds in distinct stages, starting with
larva or
nymph, optionally passing through
pupa, and ending as
adult. There are two main types of metamorphosis in insects,
hemimetabolism and
holometabolism.
The immature stages of a species that metamorphoses are usually called
larvae, and in these stages may grow quite quickly. But in the complex metamorphosis of many insect species, only the first stage is called a larva and sometimes even that bears a different name; the distinction depends on the nature of the metamorphosis.
In hemimetabolism, the development of larva often proceeds in repeated stages of growth and
ecdysis (moulting), these stages are called
instars. The juvenile forms closely resemble adults, but are smaller and, if the adult has wings, lack wings. This process is also known as "simple", "gradual" or "incomplete" metamorphosis. The differences between juveniles in different instars are small, often just differences in body proportions and the number of segments.
In holometabolism, the larvae differ markedly from the adults. Insects which undergo holometabolism pass through a larval stage, then enter an inactive state called
pupa, or
chrysalis, and finally emerge as adults. Holometabolism is also known as "complete" and "complex" metamorphosis. Whilst inside the pupa, the insect will excrete digestive juices, to destroy much of the larva's body, leaving a few cells intact. The remaining cells will begin the growth of the adult, using the nutrients from the broken down larva. This process of cell death is called
histolysis, and cell regrowth
histogenesis.
Whether the insect spends more time in its adult stage or in its juvenile form depends on the species. Notable examples are the
mayfly, whose non-eating, adult stage lives for one day, and the
cicada, whose juvenile stage live underground for 13 or 17 years. These species have incomplete metamorphosis. Typically, though not exclusively, species in which the adult form outlives the juvenile form undergo complex metamorphosis.
Many observations have indicated that
cell death plays a considerable role during physiological processes of multicellular organisms, particularly during
embryogenesis and metamorphosis.
Image:ChristianBauer Pieris rapae caterpiller.jpg|Pieris rapae larva
Image:ChristianBauer Pieris rapae caterpiller2.jpg|Pieris rapae pupa
Image:ChristianBauer Pieris rapae cocoon.jpg|Pieris rapae pupa, ready to hatch.
Image:ChristianBauer Pieris rapae youngadult.jpg|A Pieris rapae adult
Hormonal control
Insect growth and metamorphosis are controlled by
hormones synthesized by
endocrine glands near the front of the body.
Some
cells of an insect's
brain secrete a hormone that activates
thoracic glands, which secrete a second hormone, usually
Ecdysone (a
steroid), that induces metamorphosis.
Moreover, the
corpora allata produce the
juvenile hormone, whose effect is to prevent the development of adult characteristics while allowing
ecdysis. Therefore, the insect is subject to a series of molting, controlled by
Ecdysone, until the production of juvenile hormone ceases and metamorphosis occurs.
Amphibian metamorphosis
Amphibian metamorphosis undergoes a single change from larvae, called a
tadpole, to an adult. In the typical amphibian lifecycle, eggs are laid in water. The tadpole then emerges from the egg, and swims freely within the water. The tadpole has gills, a tail and a small circular mouth. The tadpole will grow, until it begins metamorphosis. Metamorphosis begins with the development of the hind legs, then the front legs. The lungs develop, and the tadpole begins to swim to the surface of the water to breathe. The intestine shortens to accommodate a carnivorous diet, and the eyes migrate rostrally and dorsally. In
frogs the tail is absorbed by the body, for the last stage of metamorphosis.
There are many deviations from the typical amphibian lifecycle. Some species of
salamander don't need to metamorphose to be sexually mature, and will only metamorphose under certain environmental stresses. Many species of frog from the
tropics lay their eggs on land, where the tadpoles undergo metamorphosis within the egg. Once they hatch, they're immature copies of the adults, sometimes possessing a tail which is re-absorbed in a couple of days.
Further Information
Get more info on 'Metamorphose'.
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