Asexual Reproduction

Asexual Reproduction

Gemmules of the freshwater sponge spongilla.

Image courtesy of J. Houseman; BIODIDAC

Reproduction is a marvelous culmination of individual transcendence. Individual organisms come and go, but, to a certain extent, organisms "transcend" time by reproducing offspring. Let's take a look at reproduction in animals.

What Is Reproduction?

In a nutshell, reproduction is the creation of a new individual or individuals from previously existing individuals. In animals, this can occur in two primary ways: through asexual reproduction and through sexual reproduction. Let's look at asexual reproduction.

Asexual Reproduction

In asexual reproduction, one individual produces offspring that are genetically identical to itself. These offspring are produced by mitosis. There are many invertebrates, including sea stars and sea anemones for example, that produce by asexual reproduction. Common forms of asexual reproduction include:

Budding

• In this form of asexual reproduction, an offspring grows out of the body of the parent.
  
• Hydras exhibit this type of reproduction.
  

Gemmules (Internal Buds)

• In this form of asexual reproduction, a parent releases a specialized mass of cells that can develop into offspring.
  
• Sponges exhibit this type of reproduction.
  

Fragmentation

• In this type of reproduction, the body of the parent breaks into distinct pieces, each of which can produce an offspring.
  
• Planarians exhibit this type of reproduction.

Regeneration

• In regeneration, if a piece of a parent is detached, it can grow and develop into a completely new individual.
  
• Echinoderms exhibit this type of reproduction.

Parthenogenesis

• This type of reproduction involves the development of an egg that has not beenfertilized into an individual.
  
• Animals like most kinds of wasps, bees, and ants that have no sex chromosomesreproduce by this process. Some reptiles and fish are also capable of reproducing in this manner.

Advantages and Disadvantages of Asexual Reproduction

Asexual reproduction can be very advantageous to certain animals. Animals that remain in one particular place and are unable to look for mates would need to reproduce asexually. Another advantage of asexual reproduction is that numerous offspring can be produced without "costing" the parent a great amount of energy or time. Environments that are stable and experience very little change are the best places for organisms that reproduce asexually. A disadvantage of this type of reproduction is the lack of genetic variation. All of the organisms are genetically identical and therefore share the same weaknesses. If the stable environment changes, the consequences could be deadly to all of the individuals.

Asexual Reproduction in Other Organisms

Animals are not the only organisms that reproduce asexually. Yeasts, plants and bacteriaare capable of asexual reproduction as well. Bacterial asexual reproduction most commonly occurs by a kind of cell division called binary fission. Since the cells produced through this type of reproduction are identical, they are all susceptible to the same types of antibiotics.