Fragmentation as a Mode of Asexual Reproduction

Fragmentation is one of the important mechanisms that take place in multicellular organisms. As the name suggests, it involves splitting organisms into different fragments. It is a form of asexual reproduction. Fragmentation type of reproduction can be defined as splitting of organisms into different fragments, each of these fragments is capable of developing into mature, and fully grown individuals that are identical to their ancestors.

This mechanism may or may not be intentional. It is one of its main characteristics of it. Fragmentation may happen due to natural damage such as environmental damage caused by predators. It may be man-made. Because of that, these types of organisms tend to develop specific organs that could shed or break off easily. Even though fragmentation may occur without the preparation of the organism, all the fragments should be able to regenerate complete organisms for them to reproduce and to function properly.

As discussed above, fragmentation is a process of splitting. Hence, it is also known as splitting. This method of reproduction is seen in many organisms such as filamentous cyanobacteria, lichens, many plants, and molds. It is also seen in animals such as sponges, acoel flatworms, sea stars, and some species of annelid worms.

Fragmentation in Diverse Organisms

1. Fragmentation in Fungi

Fragmentation is seen in various types of fungi such as molds, yeasts, mushrooms. They do reproduction by fragmentation utilizing a specific type of structure, known as hyphae. Hyphae can be defined as each of the branching filaments that make up the mycelium of a fungus. It is a branched portion of the parent fungi body and they can easily get rid off it. During the lifecycle of hyphae, they obtain food and other nutrients from the parent fungi body. By doing this, hyphae eventually grow and become mature, and ultimately, they become ready for fertilization. Now, a piece of hyphae breaks off from the parent body and enters into a growth phase as an individual body. Eventually, they also mature and grow hyphae, and this way, the cycle continues. 

2. Fragmentation in Lichens

Lichen is a composite organism resulting from algae or cyanobacteria that live in a mutualistic relationship between filaments of multiple species of fungi. The combined lichen has different properties than those of the organisms that make up it. Lichens come in a multitude of colors, sizes and shapes. Many lichens create specialized structures that can break and disperse easily. These structures include both mycobiont hyphae and algae(phycobiont) (see soredia and isidia). Larger thallus fragments may break up when the lichen dries or because of mechanical disturbances (see the lichens reproduction section).

Fragmentation in Plants

Fragmentation in plants is a very common type of vegetative reproduction. Many trees, shrubs, nonwoody perennials, and ferns form clonal colonies by producing rhizomes or stolons to produce new rooted shoots that increase the colony's diameter. If a rooted shoot becomes detached from the colony, then there has been fragmentation. Several other natural fragmentation mechanisms

Production of highly specialized reproductive structures: On their leaves, a few plants produce adventitious plantlets that fall off and form independent plants, for example. Tolmiea Menziesii and daigremontiana kalanchoe. Others make organs such as bulbils and turions.

Parts that have a high potential to grow into a complete plant are easily lost: some woody plants like the willow shed twigs naturally. This is known as cladoptosis. The lost twigs may form the roots for the establishment of a new plant in an appropriate environment. River currents often destroy branch fragments of certain species of cottonwood growing on the banks of the river. Fragments can root and establish new plants that reach suitable environments. Some cactus and other plants have stems joined together. It can root and form a new plant when a stem segment, called a pad, falls off. Some plant leaf roots readily when falling off, e.g. Echeveria and Sedum.

In non-vascular plants, for example, fragmentation is also observed in liverworts and mosses. Small pieces of "strains" or "leaves" of moss are often dispersed by wind, water, or animals. If a fragment of the moose reaches an appropriate environment, it can create a new plant. They also produce gemmae, e.g. in Marchantiapolymorpha's splash - cups, which are easily broken and distributed.

Fragmentation is utilized by people for artificially spreading various plants. This is done by layering, division, grafting, cutting and micropropagation.

Fragmentation in Animals

Animals such as sponges and colonies of corals fragment and reproduce naturally. This method reproduces many species of annelids and flatworms.

The terms architomy, paratomy and budding are used when splitting occurs due to specific developmental changes. In architomy, the animal splits at a particular point and the two fragments regenerate the organs and tissues that are missing. The development of the tissues to be lost does not precede the splitting. The animal may develop furrows in the splitting zone before splitting. A full head must be regenerated by the headless fragment.

In paratomy, the split occurs perpendicular to the antero-posterior axis and in the posterior portion the split is preceded by the "regeneration" of the anterior structures. The two organisms align their body axis, i.e. they develop in a fashion from head to tail. Budding may be considered similar to paratomy except that the axes of the body do not need to be aligned: the new head may grow sideways or even point backward (e.g. Convolutriloba Retrogemma an acoel flatworm).

Coral

Many types of coral colonies can increase in number through natural or artificial fragmentation. Enthusiasts regularly fragment corals within reef aquarium hobby for a variety of purposes including shape control; selling, trading or sharing with others; regeneration experiments; and minimizing damage to natural coral reefs. It is possible to fragment both hard and soft corals. Among many others, Acropora, Montipora, Pocillopora, Euphyllia, and Caulastrea have shown to be highly tolerant of fragmentation. Most marine anemones reproduce through fragmentation. Longitudinal fission, where the original anemone splits through the center, forming two anemones of equal size and basal laceration, where small parts of the animal split from the base and form a new anemone.

Echinoderms

The process is usually referred to as fissiparity in echinoderms (a term that is also rarely used for fission in general). Some species can deliberately reproduce through autotomy in this way. 

Now, asexual reproduction offers several advantages and these advantages. Before using such a process, it is very important to know about both sides of the coin in order to get the most out of its results. If you need it most in the future, you will be able to use this knowledge.

List of Disadvantages of this Method of Reproduction

1. Hinders Diversity

Since only one parent's characteristics and traits are passed on to their offspring, asexual reproduction would hamper their generations of genetic diversity. This causes the organism’s population to be exactly the same. This has been a huge advantage with sexual reproduction since we can mix gene pools to ensure a diverse ecosystem.

2. It Poses Some Heritage Problems

Almost all of the time, it would require only one asexual parent from whom we can copy chromosomes and genes, meaning that genetic defects or mutations resulting from asexual reproduction would still exist in the offspring without exception. This disadvantage could even lead to much more unfavorable mutations that make asexually produced organisms susceptible to disease, which would also lead to the destruction of a large number of offspring.

3. This Can Actually Lead to An Extinction-Prone Organism

All the same characteristics and traits also involve all the same weaknesses, so we can assume that a certain parasite or predator that has evolved to kill a particular asexual organism will be able to remove its entire population. Simply put, asexual reproduction can lead to existence struggle.

4. It Carries Problems With Population Control

In essence, this form of reproduction does not control the rapid population increase in the subject organisms. As there is no competition in the evolution process, each organism is highly capable of reproduction, meaning that its population will even double in each reproductive cycle. Scientists have found, however, that the process would stop at a time when its number becomes excessive.

5. It Leads to Organisms to Not Being Able to Adapt

Organisms can react to certain things with asexual reproduction, which is then passed down to their offspring. And because the offspring produce less variation, they would become less adapted to certain environmental changes, causing them not to survive. During the larval editing stage, this method is more common.

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An Overview of the Fragmentation in Plants and Animals.

The word Fragmentation literally means breaking or splitting into pieces. And hence in Biology, it means a division of the organisms into different fragments or parts. For multicellular organisms, that is to say, organisms that consist of multiple cells or more than one cell, Fragmentation is one of the most important Mechanisms, because it is a form of asexual reproduction, in which the organism splits into two and develops into a full-grown and a matured organism which is identical to its progenitors. And sometimes this process is intentional, while the other times it is not, and it is one of the main features of it as well.

Also, students may confuse fragmentation with regeneration, and hence if you wish to learn the difference between the two, then you may like to follow Vedantu.