The budding is a form of asexual reproduction of organisms in which an unequal division occurs. The new organisms "stick out" from the parents as a bump, gem, or bud, until such time as total separation occurs.
Budding occurs in different phyla of eukaryotes and prokaryotes, from bacteria to cnidarians. This form of reproduction is especially important in fungi, bacteria, animals such as sponges and jellyfish or cnidarians.
Photograph of a Hydra viridissima specimen during the budding process (Source: Peter Schuchert via Wikimedia Commons)
Budding is a type of reproduction frequently found in organisms with colonial groups, since it represents an evolutionary advantage to establish themselves in new habitats and form new colonies.
For colonial multicellular organisms, reproduction by budding represents a significant advantage, especially just after natural disasters, since they are able to regenerate the entire colony in a short period of time and from a single individual.
Although reproduction by budding has many advantages, it can cause a deterioration of the genetic variability of the species, since generating a whole population of clones makes them very susceptible to pathogens, changes in pH and temperature, salinity, etc.
characteristics
Reproduction by budding is one of the types of asexual reproduction most frequently observed in microorganisms. This reproduction allows them to originate multiple clones of themselves fully developed metabolically and in short periods of time.
All budding offspring have developed organs similar to those of their parent. Separation from the parent does not occur naturally until the nascent offspring in the bud have fully developed organs or organelles.
At the time of separating the buds and the parents, a clear difference in size is observed between them (the offspring are much smaller). However, in a short period of time these offspring can reach the size of the parent.
Types of budding
In many of the organisms that have this type of asexual reproduction, two types of budding can be distinguished:
G
It commonly occurs when environmental conditions are full or favorable for the life of the organism and therefore the individual begins to multiply by budding to increase the size of the population and take advantage of the greatest amount of resources.
G
It occurs in response to unfavorable conditions and it is when organisms detect these conditions and, as a kind of survival radiation, try to respond to the adverse condition by increasing their number (increasing the possibility of leaving offspring).
Some zoologists consider that the definition of budding is somewhat ambiguous within the animal kingdom, since many authors include within the concept processes such as the budding of the tentacles of polyps in corals, of the proglottids of tapeworms, or of a third segment in annelids.
All these examples fall within the definition of budding, since they are all individuals or entire parts that sprout on a parent with some independence from the body that gives rise to them.
Process
In the budding process, at least five shared stages can be observed for all organisms, whether in unicellular or multicellular organisms:
1- The progenitor cell increases the volume of its cytosol between half and a quarter more than normal volume.
2- A bulge, bud or gem begins to form on the outside of the cell that increased its cytosolic volume. In the case that the organism has a cell wall, a decrease in its components is observed and the synthesis of a new envelope around the daughter cells, just in the place where the protrusion begins to be observed.
3- At the moment when the protuberance is more significant, a migration of the nucleus towards the side of it occurs. Once the nucleus of the cell is positioned on the periphery of the cell with respect to the nascent gem, it enters a mitotic process, to end up forming two exactly the same nuclei.
4- The nucleus of the progenitor cell migrates back to the center of the initial cell and the second nucleus is positioned in the center of the bud or gem. Right after that moment, the original structure of the cell wall or membrane where the gem or bud originated begins to regenerate in the progenitor cell.
5- Finally, the cell wall of the yolk and the progenitor cell finish hardening and when this step is completed, both cells become independent from each other.
Photograph of the budding process of a coral (polyps) (Source: NOAA via Wikimedia Commons)
In many organisms such as hydras, corals, and sponges, the last step may not occur, as there is some cytosolic continuity between parents and offspring. However, these descendants have complete independence in many functions, such as food, for example.
Examples
Many types of bacteria have the ability to reproduce by budding. The pathogenic bacteria of the genus Rickettsia as well as many amoeba and euglenozoan protozoan species reproduce mainly by budding.
Yeasts
Yeasts can be said to be one of the "queens" of budding, as this is the way they reproduce constantly. Even in the yeast images presented in most textbooks, small bumps or buds can be seen on the cell surface.
Yeasts during asexual reproduction by budding (Source: Bookofjude, via Wikimedia Commons)
Sea squirts
For invasive organisms, budding reproduction brings many advantages, since it allows them to spread quickly and colonize large areas. Such is the case with sea squirts, which are constantly reproducing by budding.
Sea squirts are classified by many zoologists as "meta organisms" consisting of multiple clones of the same individual. These meta organisms are known as colonies and each of the clones in a colony is called " zooids ".
Hydras
One of the model multicellular organisms for the study of reproduction by budding is hydras, since they are easy to keep in captivity and reproduce constantly.
Schematic of the budding process of a Hydra (Source: A.houghton19 via Wikimedia Commons)
In the hydras it can be observed how, from the initial peduncle, new polyps begin to "sprout" which, despite making their entire metabolism independent from the parent organism, remain attached to it. It is still debated whether they are colony-forming organisms or whether they simply lack a mechanism that separates the buds from the parents.
The phylum Cniaria, which includes corals, jellyfish and hydras, is perhaps the group of multicellular organisms with the highest frequency of asexual reproduction by budding, since this type of reproduction is essential for the growth and dispersal of colonial organisms.
References
- Brusca, RC, & Brusca, GJ (2003). Invertebrates (No. QL 362. B78 2003). Basingstoke.
- Gray, A. (1871). On hypocotyledonary gemmation. Journal of Natural History, 8 (45), 220-220.
- Hickman, CP, Roberts, LS, & Hickman, FM (1984). Integrated principles of zoology. Times Mirror.
- Monniot, C. (1992). Nouvelle-Calédonie Ascidies. XI. Phlébobranches et Stolidobranches du plateau des Chesterfield. Bulletin du Muséum National d'Histoire Naturelle. Paris (4) A, 14, 3-22.
- Solomon, EP, Berg, LR, & Martin, DW (2011). Biology (9th edn). Brooks / Cole, Cengage Learning: USA.
- Von Wagner, F. (1892). VI.-General observations on fission and gemmation in the Animal Kingdom. Journal of Natural History, 10 (55), 23-54.
- Willey, JM, Sherwood, L., & Woolverton, CJ (2008). Prescott, Harley, and Klein's microbiology. McGraw-Hill Higher Education.