The basic cellular process that makes asexual reproduction possible is mitosis, the type of cell division that produces exact copies of parent cells.
Asexual reproduction occurs by several different methods in a variety of animals:- Budding happens when a small outgrowth begins on the original organism. That outgrowth gradually becomes larger and eventually separates to create a new individual. Several species of invertebrates, including the hydra, produce offspring by budding.
- Fission occurs when the original organism grows larger and then splits in two. Sea anemones are an example of an invertebrate that reproduces asexually by fission.
- Fragmentation happens when small pieces of the original organism break off and then grow into complete individuals. Starfish are among the animals that use fragmentation to reproduce.
For organisms that are widely separated from others of their kind and for organisms that are doing well in a particular environment, asexual reproduction poses quite the advantage. Yet what makes asexual reproduction an asset for some species — the fact that it doesn’t allow for change — also makes it a disadvantage. If a disease strikes or the environment changes and all the organisms are identical, they’ll all be affected equally.
If the disease can easily kill the organisms, for example, they’ll all die. If they were the only organisms of their kind, then an entire species would be wiped out in one fell swoop. Species ultimately have a better chance of surviving changes if their members have some differences from one another.