02 Reproduction in Lower and Higher Animals - part 01 - Asexual Reproduction in animals

02 Reproduction in Lower and Higher Animals - part 01 - Asexual Reproduction in animals


Reproduction  :
  • Reproduction is one of the major life processes of any living organism. 
  • It helps in maintaining the continuity of the species. 
  • Reproduction is defined as The biological process of formation of new life forms from pre-existing similar life. 
  • It thus becomes a vital process which enables the species to survive over a long period, even though the individuals or organisms live naturally for a limited period of time i.e. their life span. 
  • Reproduction in animals occurs mainly by two methods i.e. asexual and sexual.

Asexual Reproduction in animals :
  • It is a common method among lower animals. 
  • It does not involve meiosis nor the gamete formation and fusion. 
  • The formation of progeny is by a single parent only and does not involve both the sexes, so it is called asexual reproduction. 
  • The progeny or daughter cells are genetically identical to the single parent and are also referred to as clones. 
  • The lower animals reproduce asexually by gemmule formation and budding.

Gemmule Formation: 

  • Gemmule is an internal bud formed only in sponges. 
  • It has asexually produced mass or aggregation of dormant cells, the archaeocytes capable of developing into a new organism. 
  • The archaeocytes get coated by a thick resistant layer of secretion by amoebocytes. 
  • The gemmule is formed to overcome unfavourable conditions. 
  • On return of favourable conditions of water and temperature, the gemmules hatch and develop into a new individual.
  • e.g. Spongilla.

Budding:

  • It is a simple method of asexual reproduction normally occuring in favourable conditions. 
  • It is seen in a variety of animals like coelenterates (Hydra and corals) and in some colonial ascidians. 
  • In Hydra, a small outgrowth is produced towards the basal end of the body.
  • It develops as a bud which grows and forms tentacles and develops (get transformed) into a new individual. This process is called budding. 
  • The young Hydra gets detached from the parent and becomes an independent new organism.

Regeneration: 
  • By this process, the organism can fundamentally repair or regrow or restore its lost or damaged part. 
  • Though it involves asexual processes, it differs distinctly from reproduction 
  • e.g. a damaged Hydracan regenerate its lost part. 
  • Similarly Planaria if wounded, its cells become active and regenerate lost part or organ back to its original state. 
  • They can also reproduce asexually by fragmentation. 
  • Also, it is seen in planarians that the anterior end exerts a pull on the posterior end resulting in a constriction in the middle part and splitting into two pieces. 
  • Each piece grows into a new Planaria. i.e. two clones of the original have been formed.

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