What is it called when something splits to reproduce?

In asexual reproduction, one individual produces offspring that are genetically identical to itself. Reproduction is a marvelous culmination of individual transcendence in that organisms "transcend" time through the reproduction of offspring. In animal organisms, reproduction can occur by two primary processes: asexual reproduction and sexual reproduction.

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Fragmentation
Parthenogenesis
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Organisms produced by asexual reproduction are the product of mitosis. In this process, a single parent replicates body cells and divides into two individuals. Many invertebrates, including sea stars and sea anemones, reproduce in this manner. Common forms of asexual reproduction include: budding, gemmules, fragmentation, regeneration, binary fission, and parthenogenesis.

Many hydras reproduce asexually by producing buds in the body wall, which grow to be miniature adults and break away when they are mature. Ed Reschke/Photolibrary/Getty Images

Hydras exhibit a form of asexual reproduction called budding. In this form of asexual reproduction, an offspring grows out of the body of the parent, then breaks off into a new individual. In most instances, the budding is restricted to certain specialized areas. In some other limited cases, buds may come from any number of places on the body of the parent. The offspring typically remain attached to the parent until it is mature.

Progeny are budding on the body of a sponge in the Red Sea. Jeff Rotman Photography/Corbis Documentary/Getty Images

Sponges exhibit a form of asexual reproduction that relies on the production of gemmules or internal buds. In this form of asexual reproduction, a parent releases a specialized mass of cells that can develop into offspring. These gemmules are hardy and can be formed when the parent experiences harsh environmental conditions. The gemmules are less likely to become dehydrated and in some cases may be able to survive with a limited oxygen supply.

Planaria can reproduce asexually by fragmentation. They split into fragments, which develop into adult planaria. Ed Reschke/Photolibrary/Getty Images

Planarians exhibit a form of asexual reproduction known as fragmentation. In this type of reproduction, the body of the parent breaks into distinct pieces, each of which can produce an offspring. The detachment of the parts is intentional, and if thy are large enough, the detached parts will develop into new individuals.

Starfish are able to regrow missing limbs and produce new organisms through regeneration. Paul Kay/Oxford Scientific/Getty Images

Echinoderms exhibit a form of asexual reproduction known as regeneration. In this form of asexual reproduction, a new individual develops from a part of another. This typically happens when a part, like an arm, becomes detached from the parent's body. The separated piece can grow and develop into a completely new individual. Regeneration can be thought of as a modified form of fragmentation.

This paramecium is dividing by binary fission. Ed Reschke/Photolibrary/Getty Images

Paramecia and other protozoan protists, including amoebae and euglena, reproduce by binary fission. In this process, the parent cell duplicates its organelles and increases in size by mitosis. The cell then divides into two identical daughter cells. Binary fission is typically the most common form of reproduction in prokaryotic organisms such as bacteria and archaea.

This water flea (Daphnia longispina) can be seen with developing parthenogenetic or unfertilized eggs.

Roland Birke/Photolibrary/Getty Images

Parthenogenesis involves the development of an egg that has not been fertilized into an individual. Most organisms that reproduce through this method can also reproduce sexually. Animals like water fleas reproduce by parthenogenesis. Most kinds of wasps, bees, and ants (which have no sex chromosomes) also reproduce by parthenogenesis. Additionally, some reptiles and fish are capable of reproducing in this manner.

This sea star has lost an arm which can develop into a new sea star by the asexual process of fragmentation.

Karen Gowlett-Holmes/Oxford Scientific/Getty Images

Asexual reproduction can be very advantageous to certain higher animals and protists. Organisms 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.

One major 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. A gene mutation can persist in the population as it is continuously repeated in the identical offspring. Since organisms produced asexually grow best in a stable environment, negative changes in the environment can have deadly consequences for all individuals. Due to the high numbers of offspring that can be produced in a relatively short period of time, population explosions often occur in favorable environments. This extreme growth may lead to rapid depletion of resources and an exponential death rate in the population.

This is a colored scanning electron micrograph (SEM) of puffball fungus spores. These are the reproductive cells of the fungus. Credit: Steve Gschmeissner/Science Photo Library/Getty Images

Animals and protists are not the only organisms that reproduce asexually. Yeast, fungi, plants, and bacteria are capable of asexual reproduction as well. Yeast reproduce most commonly by budding. Fungi and plants reproduce asexually through spores. Plants can also reproduce by the asexual process of vegetative propagation. Bacterial asexual reproduction most commonly occurs by binary fission. Since the bacterial cells produced through this type of reproduction are identical, they are all susceptible to the same types of antibiotics.

Learning Outcomes

Discuss asexual reproduction methods

Asexual reproduction occurs in prokaryotic microorganisms (bacteria) and in some eukaryotic single-celled and multi-celled organisms. Asexual reproduction produces offspring that are genetically identical to the parent because the offspring are all clones of the original parent. A single individual can produce offspring asexually and large numbers of offspring can be produced quickly.

In a stable or predictable environment, asexual reproduction is an effective means of reproduction because all the offspring will be adapted to that environment. In an unstable or unpredictable environment asexually-reproducing species may be at a disadvantage because all the offspring are genetically identical and may not have the genetic variation to survive in new or different conditions. On the other hand, the rapid rates of asexual reproduction may allow for a speedy response to environmental changes if individuals have mutations. An additional advantage of asexual reproduction is that colonization of new habitats may be easier when an individual does not need to find a mate to reproduce. There are a number of ways that animals reproduce asexually.

Fission

Fission, also called binary fission, occurs in prokaryotic microorganisms and in some invertebrate, multi-celled organisms. After a period of growth, an organism splits into two separate organisms. Some unicellular eukaryotic organisms undergo binary fission by mitosis. In other organisms, part of the individual separates and forms a second individual. This process occurs, for example, in many asteroid echinoderms through splitting of the central disk. Some sea anemones and some coral polyps (Figure 1a) also reproduce through fission.

Budding

Budding is a form of asexual reproduction that results from the outgrowth of a part of a cell or body region leading to a separation from the original organism into two individuals. Budding occurs commonly in some invertebrate animals such as corals and hydras. In hydras, a bud forms that develops into an adult and breaks away from the main body, as illustrated in Figure 1b, whereas in coral budding, the bud does not detach and multiplies as part of a new colony.

Figure 1. (a) Coral polyps reproduce asexually by fission. (b) Hydra reproduce asexually through budding. (credit a: G. P. Schmahl, NOAA FGBNMS Manager)

Watch a video of a hydra budding. Note that there is no audio in this video.

You can view the descriptive transcript for “Budding In Hydra” here (opens in new window).

Fragmentation

Figure 2. Sea stars can reproduce through fragmentation. The large arm, a fragment from another sea star, is developing into a new individual.

Fragmentation is the breaking of the body into two parts with subsequent regeneration. If the animal is capable of fragmentation, and the part is big enough, a separate individual will regrow.

For example, in many sea stars, asexual reproduction is accomplished by fragmentation. Figure 2 illustrates a sea star for which an arm of the individual is broken off and regenerates a new sea star. Fisheries workers have been known to try to kill the sea stars eating their clam or oyster beds by cutting them in half and throwing them back into the ocean. Unfortunately for the workers, the two parts can each regenerate a new half, resulting in twice as many sea stars to prey upon the oysters and clams. Fragmentation also occurs in annelid worms, turbellarians, and poriferans.

Note that in fragmentation, there is generally a noticeable difference in the size of the individuals, whereas in fission, two individuals of approximate size are formed.

Parthenogenesis

Parthenogenesis is a form of asexual reproduction where an egg develops into a complete individual without being fertilized. The resulting offspring can be either haploid or diploid, depending on the process and the species. Parthenogenesis occurs in invertebrates such as water flees, rotifers, aphids, stick insects, some ants, wasps, and bees. Bees use parthenogenesis to produce haploid males (drones) and diploid females (workers). If an egg is fertilized, a queen is produced. The queen bee controls the reproduction of the hive bees to regulate the type of bee produced.

Some vertebrate animals—such as certain reptiles, amphibians, and fish—also reproduce through parthenogenesis. Although more common in plants, parthenogenesis has been observed in animal species that were segregated by sex in terrestrial or marine zoos. Two female Komodo dragons, a hammerhead shark, and a blacktop shark have produced parthenogenic young when the females have been isolated from males.