Nucleus Fragmentations in Diploid-Polyploid Populations of Spined-Loaches of the Genus Cobitis Linnaeus, 1758

Abstract

Analysis of 11 diploid-polyploid samples of spined loaches of the genus Cobitis from the aquatic systems of Ukraine showed that the increase in the number of micronuclei in red blood cells positively correlates with the ploidy and cell size. In diploid individuals of parental species, micronuclei cells average 0.12%, whereas they average 0.52, 1.39, and 4.72% in hybrid triploids, tetraploids, and probable pentaploids, respectively. Since triploid and tetraploid specimens in joint colonies tend to prevail over diploid ones, it can be concluded that minor disturbances in the genetic apparatus do not significantly affect the fitness, whereas an increase in the number of chromosomal sets over four is already accompanied by dysfunctions critical to normal life activity. Apparently, it is this circumstance that has led to the absence or extreme rarity of the pentaploid states in the clonal vertebrates, whereas penta-, hexa-, octo-, and even decaploid states are common in the lower invertebrates, for example earthworms. The latter is probably due to the fact that the minimum size of the genome in earthworms is several times smaller than in teleosts, which allows lower invertebrates to increase the number of chromosomal sets by more than fourfold.