Does polyploidy occur in central European species of the family Sphaeriidae (Mollusca: Bivalvia)?

Abstract

Some representatives of the bivalve family Sphaeriidae are assumed to be polyploid. In this study, 11 sphaeriid species (nine of the genus Pisidium, one of Musculium, and one of Sphaerium) inhabiting central Europe were studied karyologically, 10 of them for the first time. Analysis revealed high chromosome numbers (from 140 to 240). To elucidate the origin of high chromosome numbers, DNA contents were measured by flow cytometry in 5 of the studied species and, for comparison, in S. corneum and S. nucleus, which are known to be diploid (2n=30). Species with high chromosome counts yielded very similar DNA contents that are not higher than in the related species with low diploid numbers. This finding contradicts a possible origin of these species by recent polyploidization or hybridization of related species. Chromosome complements of the investigated species with high chromosome numbers differ from those with low 2n in their small chromosome size and the high proportion of subtelo-or acrocentric chromosomes. This indicates their possible origin either by an ancient polyplodization event followed by chromosomal rearrangements or by multiple chromosome fissions.

Structure and meiotic behaviour of B chromosomes in Sphaerium corneum/S. nucleus complex (Bivalvia: Sphaeriidae)

“…240, Kořínková and Morávková in 2010), chiasmata are still present. However, their manifestation is delayed up to the stage which most probably corresponded to a standard diakinesis (Kořínková, unpubl.).…”

“…Another unusual characteristic of the order Veneroida is the occurrence of polyploidy in some genera (Lee 1999;Ó Foighil and Thiriot-Quiévreux 1999;Park et al 2000; Lee and Ó Foighil 2002). In the veneroid family Sphaeriidae, high chromosome numbers are considered a consequence of ancient allopolyploidization events (Lee and Ó Foighil 2002;Kořínková and Morávková 2010). Up to now, only two sphaeriid species are considered diploid-the North American Sphaerium rhomboideum (Petkevičiūt_ e et al 2007) and the Palaearctic S. corneum.…”