Around this time, some insects began to hatch from their eggs not as minuscule adults, but as wormlike critters with plump bodies and many tiny legs. In Illinois, for example, paleontologists unearthed a young insect that looks like a cross between a caterpillar and a cricket, with long hairs coating its body. It lived in a tropical environment and likely rummaged through leaf litter for food.
Biologists have not definitively determined how or why some insects began to hatch in a larval form, but Lynn Riddiford and James Truman , formerly of the University of Washington in Seattle, have constructed one of the most comprehensive theories.
They point out that insects that mature through incomplete metamorphosis pass through a brief stage of life before becoming nymphs—the pro-nymphal stage, in which insects look and behave differently from their true nymphal forms. Some insects transition from pro-nymphs to nymphs while still in the egg; others remain pro-nymphs for anywhere from mere minutes to a few days after hatching.
Perhaps this pro-nymphal stage, Riddiford and Truman suggest, evolved into the larval stage of complete metamorphosis. Perhaps million years ago, through a chance mutation, some pro-nymphs failed to absorb all the yolk in their eggs, leaving a precious resource unused. In response to this unfavorable situation, some pro-nymphs gained a new talent: the ability to actively feed, to slurp up the extra yolk, while still inside the egg.
If such pro-nymphs emerged from their eggs before they reached the nymphal stage, they would have been able to continue feeding themselves in the outside world. Over the generations, these infant insects may have remained in a protracted pro-nymphal stage for longer and longer periods of time, growing wormier all the while and specializing in diets that differed from those of their adult selves—consuming fruits and leaves, rather than nectar or other smaller insects.
Eventually these prepubescent pro-nymphs became full-fledged larvae that resembled modern caterpillars. In this way, the larval stage of complete metamorphosis corresponds to the pro-nymphal stage of incomplete metamorphosis. The pupal stage arose later as a kind of condensed nymphal phase that catapulted the wriggly larvae into their sexually active winged adult forms. Some anatomical, hormonal and genetic evidence supports this evolutionary scenario.
Anatomically, pro-nymphs have a fair amount in common with the larvas of insects that undergo complete metamorphosis: they both have soft bodies, lack scaly armor and possess immature nervous systems. A gene named broad is essential for the pupal stage of complete metamorphosis. If you knock out this gene, a caterpillar never forms a pupa and fails to become a butterfly. The same gene is important for molting during the nymphal stage of incomplete metamorphosis, corroborating the equivalence of nymph and pupa.
Likewise, both pro-nymphs and larvae have high levels of juvenile hormone, which is known to suppress the development of adult features.
In insects that undergo incomplete metamorphosis, levels of juvenile hormone dip before the pro-nymph molts into the nymph; in complete metamorphosis, however, juvenile hormone continues to flood the larva's body until just before it pupates. The evolution of incomplete metamorphosis into complete metamorphosis likely involved a genetic tweak that bathed the embryo in juvenile hormone sooner than usual and kept levels of the hormone high for an unusually long time.
However metamorphosis evolved, the enormous numbers of metamorphosing insects on the planet speak for its success as a reproductive strategy.
The primary advantage of complete metamorphosis is eliminating competition between the young and old. Larval insects and adult insects occupy very different ecological niches. One of the most dramatic forms of metamorphosis is the change from the immature insect into the adult form. Most of the major insect orders have a typical life cycle which consists of an egg, which hatches into a larva which feeds, moults and grows larger, pupates, then emerges as an adult insect that looks very different from the larva.
Typical holometabolous insect groups are the Coleoptera Beetles , Lepidoptera moths, butterflies and skippers and Hymenoptera sawflies, wasps, ants and bees and Diptera flies. All of these groups have a life cycle where the egg hatches into a larva e. These groups go through gradual changes as they turn into adults. Immature forms of these insects are called nymphs and these gradually increase in size and change form.
As the insect grows, it sheds its skin called moulting. After each moult, the nymph looks a bit different or a bit bigger. After a final moult, the full adult form emerges.
Metamorphosis is one of the key elements that makes insects so successful. Many insects have immature stages with completely different habitats from the adults. This means that insects can often exploit valuable food resources while still being able to disperse into new habitats as winged adults. The potential for adaptation and evolution is greatly enhanced by metamorphosis. There is an important feature to note regarding metamorphosis.
Insects are not able to mate and reproduce until they undergo their final moult or emerge from a pupa as a winged adult. Wings do not appear until the final moult the one exception to this is the Ephemeroptera, or Mayflies. When you see an insect with wings, it is fully grown. This means that small flies do not become larger flies, they are as big as they will get.
Holometabolous larvae are larvae that pupate before emerging as adult insects, and include many of the most familiar insects. Holometabolous larva in general are little more than tubular, efficient eating machines. They do not have to lay eggs, or find a mate. Apart from eating, they are mainly concerned with avoiding being eaten themselves. This means that they may have good camouflage, or hide in shelters or holes, or they may taste dreadful to any prospective predators.
The major insect orders have larvae with different common names. For instance, moths, butterflies and skippers have larvae which are usually called caterpillars. Fly larvae are nearly always called maggots. A: No, but certain types of animals have similar life cycles. For example, mammals and reptiles have very different life cycles from each other, but a horse and a cat have similar life cycles because they are both mammals. There are three different plant life cycles: haploid 1n , diploid 2n , and the more common haploid-diploid 1n-2n.
Life cycle means the stages a living thing goes through during its life. In some cases the process is slow, and the changes are gradual. Humans have various stages of growth during their lives, such as zygote, embryo, child and adult. The change from a child to an adult is slow and continuous.
Begin typing your search term above and press enter to search. Press ESC to cancel. Skip to content Home Arts What is an advantage of complete over incomplete metamorphosis? Ben Davis February 11, What is an advantage of complete over incomplete metamorphosis? What is the difference between complete metamorphosis and incomplete metamorphosis What are advantages of complete metamorphosis?
What is the main disadvantage of complete metamorphosis?
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