Cyclic Polyploidy in Obligate Agamic Amoebae

Abstract

It is considered that asexual reproduction of organisms should lead to accumulation of harmful mutations in a series of successive generations (the so-called “Muller’s ratchet”). Accordingly, effective mechanisms for “nulling” this effect should exist in the life cycle of obligate agamic protists. According to one hypothesis, a so-called “cyclic polyploidy” (or agamic ploidy cycle) can act as such a mechanism. Lobose amoebae Amoeba proteus and closely related species are obligate agamic organisms. The karyological analysis that we conducted, as well as a detailed study of the cell cycle of A. proteus and A. borokensis using optical tomography, allow us to conclude that these organisms have a special kind of cyclic polyploidy. The euploid state of the nucleus takes a completely insignificant period of time relative to the duration of the entire nuclear cycle of these amoebae, the stages of meta- and telophase of mitosis, whereas the rest time of the cycle is associated with the aneuploid state of the nucleus.