FRAGMENTATION (BIOLOGY): IN ANIMALS, IN PLANTS AND EXAMPLES - BIOLOGY - 2025

The fragmentation is a type of asexual reproduction in the spontaneous rupture of an organism occurs in two or more fragments. Each of these fragments has the ability to regenerate a complete individual, thus increasing the number of clones in a population.

Although this type of reproduction has been observed in colonial bacteria and in animal and plant multicellular organisms, it continues to be a controversial focus in the world of science, as many researchers argue about the evolutionary relevance of this reproductive method.

Photograph of a blue starfish (Linckia laevigata) (Source: Frédéric Ducarme via Wikimedia Commons)

Some authors consider that the modes of fragmentation in nature include both binary fission in bacteria and collective fragmentation and the production of unicellular propagules in multicellular organisms.

Whatever the view of this process, fragmentation is a type of asexual reproduction that can occur "intentionally" or that can be mediated by environmental stressors, as well as anthropological intervention.

This type of reproduction is not preceded by a meiotic division event, that is, it does not involve syngamy or gametic fusion, but even so the resulting fragments can regenerate a new individual identical to the one that was fragmented.

The size and number of fragments that an organism can produce by fragmentation is highly variable, as is the size of the offspring. One difference between fragmentation and other types of asexual reproduction is that it does not require the investment of energy, as opposed to fission or budding, for example.

Fragmentation in animals

Fragmentation has been described as a reproductive strategy for many invertebrate animals, among which are flatworms (flatworms), annelids (earthworms), some echinoderms (starfish) and cnidarians (corals and anemones).

Earthworms also reproduce by fragmentation (Source: Fir0002, via Wikimedia Commons)

Usually, the division of one of these invertebrates into one or more fragments ends with the regeneration of the "missing parts" in each one. This illustration shows a starfish that has fragmented:

Fragmentation vs. Regeneration

Starfish can fragment, but fragmentation is different from regeneration. It is common to confuse the fragmentation process with the regeneration process and a clear example of this has to do with starfish, which are a type of echinoderm.

Like many other organisms, starfish can regenerate their arms in short periods of time when they lose them due to various circumstances (biotic or abiotic). Unfortunately, many general texts describe this process as a fragmentation event, a fact that is not necessarily true.

When a starfish fragments it is true that it can regenerate the parts it lost, but in reality the lost fragments die before re-forming the body of the animal.

Only starfish belonging to the genus Lickia, such as the blue starfish Lickia laevigata, can regenerate new individuals from the portions resulting from an accidental fragmentation process, whether of natural origin or not.

In plants

Plants can also reproduce vegetatively by fragmentation and represent perhaps the most relevant example of asexual reproduction assisted anthropologically or, what is the same, directed by human intervention.

Many plant organisms can multiply clonally by fragmenting some of their body regions into "portions" that can give rise to a new individual genetically identical to the parent.

One of the properties of plants that favors this process is the ability of some of their cells to “restart” their genome, de-differentiating, and divide to give rise to new cell lines that will differentiate into the specific organs and tissues of the new clone.

The most common examples of horticultural techniques for plant propagation that rely on asexual reproductive capacity by fragmentation include the use of "cuttings" or "cuttings", as well as multiplication through portions of reserve structures such as tubers and bulbs.

In the natural environment, many ferns, trees, shrubs and other perennial non-woody plants can reproduce by fragmentation of the rhizomes that have developed new shoots.

How does fragmentation occur in plants?

When a plant reproduces by fragmentation, either natural or artificial (caused by a human being), in each fragment there is the growth and differentiation of adventitious roots (which are in different places than where they should be).

The production of these roots allows the attachment of the new plant in formation to the substrate, from where it obtains hydration and mineral nutrients. Later on, from the “rooted” fragment a new shoot emerges, with its apical meristem, its branches and its leaf blades (depending on the case).

Specific examples of species that reproduce by fragmentation

A coral

The coral species Palythoa caribaeorum, belonging to the phylum Cnidaria, to the Anthozoa class and to the Zoantharia order, is a good example of invertebrate animals that reproduce by fragmentation.

In a study carried out in two coastal areas of Brazil, Acosta et al. (2001) showed that reproduction by fragmentation in this species did not depend on internal signals or stimuli, but rather on a large number of exogenous factors.

According to their nature, this author classifies such factors as "biotic" and "abiotic". Biotics are those that cause the isolation of tissue fragments through injuries, often related to cases of partial mortality of the colonies.

Instead, exogenous abiotic factors have to do with physical fragmentation that results in the "breaking" of an individual into one or more fragments due to physical forces such as storms, currents, waves or strong tides. These forces can also include some caused by human intervention, such as anchoring, manipulation by divers, etc.

A plant

Plectranthus scutellarioides, popularly known as "coleus", is a Magnoliophyta plant belonging to the Lamiaceae family. It is characterized by its various color variations and is highly sought after in garden design.

This plant is commonly reproduced by "cuttings" or "fragments" of its stems or leaves, from which new individuals are obtained. The appearance of adventitious roots and the "regrowth" of these plants is relatively fast, and can be observed in a matter of a few days.

References

1. Acosta, A., Sammarco, PW, & Duarte, LF (2001). Asexual reproduction in a zoanthid by fragmentation: the role of exogenous factors. Bulletin of Marine Science, 68 (3), 363-381.
2. Brusca, RC, & Brusca, GJ (2003). Invertebrates (No. QL 362. B78 2003). Basingstoke.
3. Egger, B. (2008). Regeneration: Rewarding, but potentially risky. Birth Defects Research Part C: Embryo Today: Reviews, 84 (4), 257-264.
4. Hickman, CP, Roberts, LS, & Larson, A. (1997). Integrated principles of zoology. 10th edn. Boston: WCB.
5. Highsmith, RC (1982). Reproduction by fragmentation in corals. Marine ecology progress series. Oldendorf, 7 (2), 207-226.
6. Pichugin, Y., Peña, J., Rainey, PB, & Traulsen, A. (2017). Fragmentation modes and the evolution of life cycles. PLoS computational biology, 13 (11), e1005860.
7. Solomon, EP, Berg, LR, & Martin, DW (2011). Biology (9th edn). Brooks / Cole, Cengage Learning: USA.