One of the ontogeny characteristics is a life expectancy. It mainly depends on duration of development stages . Embryonic development of all plants a

Animal development stages [Life cycle]

One of the ontogeny characteristics is a life expectancy. It mainly depends on duration of development stages. Embryonic development of all plants and animals is always shorter than post-embryonic development, which is considered to be the period of life of the organism.

In animals with a direct type of development, life starts from birth and continues until death. In organisms with the metamorphosis part of his life is the larvae stage.

It is obvious that at the stages of larvae and pupae, insects go through all stages of development and there are fully matured and grown, then it only remains their reproduction. Whereas vertebrate larva — yet an embryo, which, though already able to eat on its own, but in order to reach the adult stage of development, it needs a long time to grow and mature in the post-larval stages.

Vertebrates

In vertebrates, it occupies a very little of its lifetime. In oviparous Osteichthyes larval stage lasts from several days up to several weeks, and the growth, maturation and maturity of the organism, depending on its species, last three-four, ten or even more than a hundred years. In frogs, the tadpole development takes one-two months, and a further period of life can last more than 10 years. Taken from http://worldofschool.org

Diagram 92. Mayfly — insects of a stand-alone order, which in the adult state live so short, that they don’t have a functioning digestive system

Insects

Insects have a completely different situation — larval stage is usually much longer the adult stage. This adult stage of life, where insects do not grow and develop, is called imago (from Latin “imago” — “image”). Some insects such as mayflies (diagram 92) or chironomids do not even eat during this period, as in the adult state their digestive system is underdeveloped. As a result, their adult period of life lasts only a few days. During this time, the copulation occurs and females lay eggs. Despite the fact that the stage of the larvae of these insects takes a few months, often say that they live only a few days. In other species of insects, that as adults are well-fed, imago stage can last for several weeks or months, while the larva lives for several years. For example, the flight of cockchafers lasts two to three weeks and the larva develops in the ground for three years. The champion among insects in life expectancy in the larval stage is the periodical cicadas. Its larva burrows deep into the ground, where develops for 16 years. There are some exceptions among insects — females of social insects. Thus, female-queens of honey bees live up to 5 years, and of ants — even up to 15.

Questions:
  • Why embryonic period is always much shorter than a period of postnatal ontogenesis?

  • What are the reasons for differences of development stages in vertebrates and insects?