Consecutive endopolyploidy levels in cells of <i>Branchipus schaefferi</i> Fisher, 1834 (Branchiopoda: Anostraca)

Abstract Endopolyploidy is a well-documented phenomenon in the natural world, yet its biological significance remains poorly understood. A multitude of effects and consequences have been described in the literature as being attributable to this phenomenon, yet none of them have been subjected to rigorous and well-established confirmation. The measurement of ploidy level is typically conducted using flow cytometry or densitometry techniques. Conversely, direct chromosome counting is a less frequently employed method. As a result, all published ploidy-level counts have been presented as even numbers. We describe the first ploidy level chromosome count in somatic cells of Branchipus schefferi Fischer, 1834, a common and one of the most abundant branchiopod crustaceans (Branchiopoda, Anostraca) widely distributed across Europe. The range of observed ploidy levels was found to vary from diploid to octoploid cells, including odd numbers (3n, 5n, and 7n), as well as different aneuploid numbers. It was furthermore observed that chromosomes at higher ploidy levels undergo an apparent telomere-binding process, leading to the appearance of interphase cells with a large nuclear volume. The possible origins of ploidy levels and the consequences of chromosome joining are discussed here.