n., plural: fragmentations
Definition: breaking into smaller parts, as in asexual reproduction wherein a parent organism breaks into fragments
Table of Contents
What is fragmentation? In general, fragmentation refers to the state or the process of breaking into smaller parts, called fragments. In biology, it may refer to the reproductive fragmentation process as a form of asexual reproduction or to a step in certain cellular activities, such as in apoptosis and DNA cloning.
Fragmentation in Reproductive Biology
The process of fragmentation is one of the most important mechanisms that mostly occur in a multicellular organism (i.e. the organism that is made up of more than a single cell). In Reproductive Biology, fragmentation refers to the process by which a living organism split into parts that later grow identical to the original organism. The various bodies or parts that are formed due to such a process are referred to as fragments and exemplifies asexual reproduction.
In fragmentation, the fragments are formed due to the splitting of various living organisms. Each of the formed fragments after going through the cycle of growth develops into a mature, fully-grown individual that is identical to its parent with respect to shape, size, and other dimensions. (Ref. 1)
The main characteristic of the process of fragmentation is that this process can occur both intentionally and unintentionally. For instance, man-made causes or environmental changes may cause the organism to fragment and eventually develop into complete and mature organisms that are similar to the parent.
Fragmentation is found in both animals and plants. Fungi, lichens, molds, worms, sea stars, acoel flatworms, and sponges are some of the common examples where the mode of reproduction occurs via fragmentation. The image below shows the fragmentation in a starfish. It can be seen that the fragmenting body gets separated from the arm of the starfish and after some time it starts developing into a new starfish as seen in Figure 1.
Fragmentation and Splitting
The process of fragmentation is indeed the process of breakage of an organism into various fragments that over time gets developed into a complete organism. Thus, this process is also referred to as the process of splitting.
Process of Reproduction
The biological process by which new individuals/organisms are formed from the parents is called reproduction. Sexual and asexual are the two forms of reproduction that are broadly studied by many researchers. The process by which the offspring are born due to the mating of two parents is called sexual reproduction. Each of the parents contributes an egg from a female and a sperm from a male and after the combination of these two gametes through the process of fertilization, a zygote is formed that matures into an embryo and finally into a fully-grown organism. Allogamy, internal fertilization, external fertilization, and autogamy are some of the types of sexual reproduction. The process of sexual reproduction has been elaborated in Figure 2.
The process by which the cycle of reproduction is achieved by only one parent is called asexual reproduction. Examples include binary fission, budding, fragmentation, and parthenogenesis. The process of binary fission is found in bacteria wherein a single bacterium tends to divide into two cells. In budding, very small organs are formed in the bodies of the parent and thus after some time, they tend to break and thus finally grow into two individuals. This type of asexual reproduction is found in yeasts and some other hydra animals. (Ref. 2) In fragmentation, reproduction occurs via breakage of the parent organism into various fragments that have the ability to grow identical to their parents. It is commonly found in coral, sponges, and starfishes. In parthenogenesis, this type of asexual reproduction is found in many fishes, reptiles, and amphibians.
For comparisons between sexual reproduction and asexual reproduction, see the Table below:
Table 1: Sexual and Asexual Reproduction Comparison
|Sexual Reproduction||Asexual Reproduction|
|Two parents are involved||A single parent is involved|
|An egg is fertilized by sperms||The new organism is formed from the parent and both of them are identical to each other|
|Found in humans, many plants, and many animals||Found in bacteria, reptiles, certain animals, and many plants|
|The offspring are different from their parents in many main aspects||The offspring are identical to their parents and ancestors|
|Process is time-consuming but with leads to greater genetic variations in the next generation||Process is relatively faster but there are no/limited genetic variations in the next generation|
Fragmentation – General Steps
The process of fragmentation is very vital in biology for asexual reproduction. As described earlier, this is the form of reproduction in which small organs or parts of the body of the parent individual get separated and finally grows into a completely mature organism. Let us take an example of Planaria, one of the many flatworms, belonging to the class of Rhabditophora and phylum Platyhelminthes. See Figure 3 for the depiction of fragmentation and the step involved during fragmentation in Planaria.
Fragmentation and Regeneration
The words fragmentation and regeneration are often referred to as the words used in the reproduction. Still, there are some common differences in them that are quite evident. The process of fragmentation often occurs when a part of an organism is broken into smaller fragments that can grow in to separate identical organisms whereas regeneration is one in which the organism is capable to regrow certain body parts that are lost. In essence, new species are formed following fragmentation whereas new organs are formed during regeneration. It is believed all organisms are capable of regenerating their lost body parts while there are only a few that have the ability to reproduce through fragmentation. The process of regeneration can be found in lizards and octopi. The details of fragmentation and regeneration can be found in Figure 4. (Ref. 3)
The prime advantage of fragmentation is that it can be achieved with only a single parent as the mating between male and female is not mandatory. The whole cycle of reproduction can easily be achieved by the formation of the fragments from the bodies of the parent organism and then their growth and transformations into new identical organisms to their dynasties. The second important advantage of the process of fragmentation is that its reproduction cycle can be achieved in a relatively less amount of time. The whole time that is wasted during the mating season and conditions in the sexual reproduction is avoided in the reproduction through asexual systems. Thus, fragmentation being a type of asexual reproduction is a very rapid process. Moreover, since fragmentation is a very fast process of producing offspring, it is believed that a relatively larger number of organisms can be produced in a shorter time as the chain of reproduction goes from one individual to two and from two to four. Hence, in less time a whole new generation of identical organisms can be produced from a single parent via fragmentation. Finally, another advantage that makes the process of fragmentation very vital in biology is its capability to occur and progress in any environment and any climatic conditions. (Ref. 4)
Although it can be perceived from the above discussion that asexual reproduction especially fragmentation plays a very vital role in maintaining the equilibrium in the ecosystem by producing larger organisms in relatively less time but still there are many disadvantages associated with this process. The major disadvantage of fragmentation is associated with biodiversity.
Asexual reproduction is carried out by a single parent and due to this only its traits, genes and characteristics will be passed on to the new generation. Without much genetic diversity, the next generation tends to be very identical to each other Conversely, in sexual reproduction, two genes from both parents are mixed. This gives rise to a genetically diverse offspring.
The second disadvantage of fragmentation is that the same heritage problems that once found in the parents will likely be manifesting in the next generation. This process arises all the time in asexual reproduction, the same traits and chromosomes are copied and transferred on all offspring. As a result, the offspring may be subjected to an early extinction due to some of the diseases that they inherited.
Species produced via fragmentation tend to be identical. And so, weakness in their bodies may make them susceptible to parasitic and predator attacks. This might cause them to struggle to survive. If additional pressure comes along, for instance, a sudden shift in the environment or habitat, the species could struggle even more and eventually could be eliminated and be extinct. In contrast, such problems are less likely to occur in sexual reproductions because it promotes greater biodiversity.
In essence, fragmentation in biology carries problems with the control in the population as this is a chain process in which an organism divides into two and then another two are formed from the fragments. This leads to the reproduction of massive populations from a single parent.
Examples of Fragmentation
The process of fragmentation is found in plants, animals and diverse microscopic organisms as a form of reproduction.
Fragmentation in Fungi and Algae
The fragmentation is very commonly seen in both fungi and lichens. Molds, yeasts, and mushrooms are some of the types of fungi where reproduction is achieved via asexual fragmentation. The special type of structure that is achieved for the process of splitting is referred to as hyphae. They are the filamentous branches from which the mycelium of the fungi is made. They are the branches of the mother fungi from where they can be detached easily and transform themselves. Before the process of splitting, the hyphae grow on the fungi from where they obtain the food and water that are essential for growth and nourishment. Once the hyphae are mature enough to feed on their own and reproduce they detach from the parent body and live independently. Certain algae also reproduce by fragmentation. For example, filamentous algae, such as Spirogyra, reproduce by cutting itself into fragments.
Fragmentation in Plants
The fragmentation in plants is most commonly described as the vegetative type of fragmentation. In plants, mostly the diameter of their colonies is enhanced by producing new root and shoot systems via the dispersion of rhizomes or stolon from the old trees, shrubs, ferns, and perennials. Thus, once the root is detached from the colony, it tends to grow on its own thus giving rise to a completely new root system. Other common examples of natural fragmentation are as follows:
- Woody plants, e.g. willows, shed twigs quite effortlessly and under the appropriate environmental conditions may grow into a new plant. This natural shedding of twigs is known as cladoptosis.
- Detaching of plant parts to become a new organism is also observed in non-woody plants, such as Kalanchoe daigremontiana. In the photo below, notice the adventitious plantlets on the leaf of K. daigremontiana. The plantlests could drop off and subsequently take root to the ground to become a new and independent plant.
- Nonvascular plants, such as mosses and liverworts, reproduction by fragmentation is also common. Merchantia polymorpha (common liverwort) is an example of a nonvascular plant that does fragmentation by producing gemmae that are broken off the original plant to become a new and independent plant.
Below is the video depicting the occurrence of fragmentation in plants and its importance to them.
Fragmentation in Animals
Fragmentation is observed in many coral colonies. Both hard corals and soft corals can be fragmented easily. Similarly, breeds like Montipora, Acropora, Pocillopora, Euphyllia, and Caulastrea are capable of fragmentation. Many marine anemones reproduce themselves via the process of splitting or fragmentation. Other examples of animal fragmentation are those of starfish and Planaria, which have been elaborated in the previous sections. (Ref. 5)
Fragmentation in Cell and Molecular Biology: Definition and Biological Importance
Let’s take a look at the cellular level of the reproductive fragmentation process. DNA cloning refers to the duplication of the DNA molecules — the creation of an exact copy or a “clone” of DNA, especially for asexual reproduction. Through natural means, an organism creates identical DNA molecules for its “clone” (offspring). The word cloning here refers to the fact that the reproduced individuals exhibit identical DNA to that of its ancestor. This occurs at fragmentation. However, it is not an exclusive process as DNA cloning occurs in other forms of asexual reproduction as well, such as binary fission. Thus, DNA cloning is an important cellular process in asexual reproduction.
DNA cloning can be achieved both naturally as well as via artificial methods. Researchers made use of this process in laboratories for research and experimental studies. They came up with the so-called “DNA fragmentation” procedure, which is a molecular genetic technique that allows them to cleave and clone specific DNA fragments from an organism’s genome via recombinant DNA technology.
Apart from this molecular aspect of the use of fragmentation, the term is also used to describe another cellular process wherein cellular parts undergo fragmentation. This is seen especially in apoptosis. Apoptosis is the process in which the programmed destruction of cells occurs and it is achieved by a very organized sequence of morphological changes. Moreover, the morphological changes are characterized by cellular and nuclear shrinkage, chromatin fragmentation and condensation, the formation of apoptotic bodies, and the process of phagocytosis of all the available neighboring cells. Additionally, apoptosis involves the uniform endonucleases activations with the cleavages of DNA in the fragments of either one hundred and eighty base pairs or the multiples of the one hundred and eighty base pairs. Thus, the relation between apoptosis and DNA fragmentation plays a very major role in maintaining cellular organization. The progression of cell apoptosis plays a key role in saving the healthy cells and tissues working in the human body from the hazardous effects of the cells that aren’t working stably and are in the process of dying.
The biological process by which the organisms split into two or more fragments to become new individuals (offspring) is called fragmentation. These fragments grow and mature into a whole new generation with identical characteristics to their parents. Fragmentation is also referred to as splitting in various literature and are the synonyms of each other. The process of fragmentation is asexual, which means that only a single parent is involved. Therefore, the offspring most likely will carry the same genetic characteristics. On the other hand, the reproduction in which both male and female parents are involved is known as sexual reproduction. Both types of reproduction have their pros and cons.
Fragmentation occurs in three stages. The process begins with the formation of fragments. This is followed by the development of fragments, and then, ends at the conversion of fragments into developed species. The whole cycle of asexual reproduction especially fragmentation is of great biological importance. The formation of identical species, lesser time of reproduction, and transfer of positive genes from parent to offspring are some of the key advantages of fragmentation whereas the lack of or the reduced genetic diversity, same heritage problems, and unable to cope up with the environmental changes are some of the disadvantages of it.
Fragmentation is also used to refer to certain cellular processes. As fragmentation refers generally to the breaking or cutting of a large entity into smaller parts, it is used to pertain to cell processes such as DNA fragmentation (occurring during DNA cloning) and cell fragmentation, which is particularly the final stage of apoptosis.
The two main areas where fragmentation plays a very vital role in the biological cells are apoptosis and DNA cloning. In DNA cloning part of the genes are transferred from the main body to fragments whereas in apoptosis, the decay of dead cells occurs.
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