Budding

BUDDING, one of the types of asexual reproduction found in both protozoa and multicellular animals (sponges, coelenterates, worms, and lower chordates). A distinction is made between simple (with the formation of 1 bud) and multiple budding (with the simultaneous formation of many buds). Simple budding is a modification of binary fission, from which it differs primarily in the inequality of the products of division. Whereas in fission the individual splits into two daughter individuals of equal size, in budding the original individual, which is called the maternal one, separates from itself a certain small part (the daughter individual), which only gradually grows and reaches the size of the maternal one: simple budding is unequal division. Most often, budding is external in nature, consisting of an outgrowth on the surface of the maternal organism, with the main germ layers of the maternal individual usually continuing into the bud. In other cases, budding consists of the isolation of certain groups of cells within the budding organism (internal budding), which groups then fold into the forming bud; such are gemmules (see) in sponges and statoblasts in bryozoans. The emergence of internal buds to the outside is often preceded by the death and disintegration of the maternal organism. Budding can take place either at any point on the body of the organism or only at certain well-defined places, such as, for example, the budding zone encircling the body of a hydra, or the so-called budding stolon [a special outgrowth on the ventral side of the body of many tunicates (ascidians and salps), which possesses enhanced growth and is the site of bud formation]. Some authors consider strobilation to be a special type of budding, consisting of the sequential separation of a series of buds from one end of the maternal individual; this includes the budding of scyphistoma or the polypoid stage of scyphomedusae, and perhaps also the formation of a series of segments in the strobila of tapeworms. Very often, a regular alternation of budding with sexual reproduction is observed, as a result of which the life cycle of the animal acquires the character of an alternation of generations (coelenterates, salps among tunicates, etc.). The formed buds either immediately develop into an organism similar to the maternal one, or perform this process only after a certain period of time—resting buds (gemmules of sponges, statoblasts of bryozoans). Budding that is not carried to completion leads to the formation of colonies, for example, in sponges, hydroid and scyphozoan polyps, bryozoans, and some others.

V. Dogel.