Indirect development is typical for ... Indirect postembryonic development: examples

Development is an indispensable factor in life. It begins with a fertilized egg and ends with puberty. Direct and indirect development is characteristic for the postembryonic period. Direct development is a biological process in which a multicellular organism grows and grows, complicating its organization. This phenomenon is typical for humans, fish, birds and mammals.

Indirect development is a process in which the embryo develops into a mature individual with the involvement of the larval stage, which is accompanied by metamorphosis. This phenomenon is observed, for example, in most invertebrates and amphibians.

Features of the postembryonic period

Periods of postembryonic development are accompanied by a change in morphological features, habits and habitats. For direct development, a characteristic feature is that, after birth, an embryo is a reduced copy of an adult organism, it differs only in size and lack of certain characteristics that are acquired only with time. An example can be the development of man, animals and some reptiles. Indirect development is characteristic of invertebrates, mollusks and amphibians. In this case, the embryo has significant differences in comparison with the adult animal. An example is an ordinary butterfly. Only after several stages of development have been passed, the small larva will be transformed beyond recognition.

Periods of development

Periods of postembryonic development include juvenile stage, maturity and aging.

• The juvenile period covers the time from birth to puberty. This stage is accompanied by adaptation to the new environment. It should be noted that many animals and reptiles, for which the direct path of postembryonic development is characteristic, develop approximately equally. The only difference is the time frame. This period ends with puberty.

• The period of maturity, called the reproductive stage, is characterized by a halt in growth. In the body there is a self-renewal of certain structures and their gradual deterioration.
• The aging period is accompanied by a slowing down of the recovery processes. As a rule, there is a decrease in body weight. If there was no violent intervention, then natural death occurs when vital systems as a result of the slowdown of all processes cease to function.

Indirect development: examples and stages

Let's look at how life in a new being is born. Direct and indirect development are terms that describe the various processes of animal life that begin with a fertilized egg. During the postembryonic development, organ systems are finally formed, growth is observed, sexual maturation followed by the continuation of the genus. Then aging takes place, and in the absence of external interventions, a natural death occurs.

• Immediately after birth, a number of transformations begin. At this time a small organism differs from an adult both externally and internally.
• The second stage is the transformation into a completely new body. Metamorphosis is a postembryonic change in the shape of the body with an alternation of several stages.
• The third stage is the final stage, which ends with puberty and the continuation of the genus.

Characteristics of indirect development

Indirect development is characteristic of multicellular organisms. A larva emerges from the laid egg, which, outwardly and internally, does not resemble an adult. In structure, this is a simpler being, usually smaller in size. Its appearance can be remotely similar to its distant ancestors. An example is a larva of such an amphibian as a frog.

Externally, the tadpole looks like a small fish. Due to the presence of special larval organs, he can lead a completely different life than the mature individuals. Even rudimentary sexual differences they do not, so the sex of the larvae can not be determined. At a certain number of species of animals, this stage of development occupies most of their life.

Radical metamorphosis

With indirect development, the newborn is very different from the sexually mature form in a number of anatomical characters. The embryo hatch from the egg in the form of a larva, which undergoes radical metamorphosis before reaching its adult stage. Indirect development is characteristic of animals that lay numerous eggs. These are some echinoderms, amphibians and insects (butterflies, dragonflies, frogs and so on). The larvae of these creatures often occupy a completely different ecological space, rather than an adult animal. They feed, grow and at a certain point are transformed into an adult animal. These global metamorphoses are accompanied by numerous physiological changes.

Pros and cons of direct development

The plus of direct development is that for growth, much less energy and vital ingredients are needed, since no global rearrangements in the body occur. The disadvantage is that for the development of the embryo, you need a large supply of nutrients in the eggs or bearing in the womb of the mother.

Negative point is also that between young and adult animals there can be competition within the species, since their habitat and food sources coincide.

Pros and cons of indirect development

Due to the fact that organisms with an indirect type of development live in different ecological niches, a competitive relationship between larvae and adults, as a rule, does not arise. The advantage is also that the larvae of inactive beings help the species to expand the range of its habitat. Among the minuses is to point out that the indirect development of animals in an adult often lasts a long period of time. For qualitative transformations, a large number of nutrients and energy are needed.

Types of indirect development

The following types of indirect development are distinguished: with complete and partial metamorphosis. With complete transformation, indirect development is characteristic of insects (butterflies, beetles, some hymenoptera). The newly introduced larvae begin to eat, grow, and then become immovable cocoons. In this state, all the organs of the body decay, and the formed cellular material and accumulated nutrients become the basis for the formation of completely different organs that are characteristic of the adult organism.

With partial metamorphosis, indirect postembryonic development is characteristic of all species of fish and amphibians, certain species of worms, mollusks and insects. The main difference from the complete transformation is the absence of the cocoon stage.

The biological role of the larval stage

The larval stage is the period of active growth and the supply of nutrients. Appearance, as a rule, is very different from the adult form. There are unique structures and organs that the adult does not have. Their diet can also vary significantly. Larvae are often adapted to the environment. For example, tadpoles live almost exclusively in water, but can live on land like adult frogs. Some species in the adult stage are immobile, while their larvae move and use this ability to resettle and expand the habitat.