the diversity of chromosome structure of males in cobitis (teleostei, cobitidae) populations

The populations of Cobitis distributed in Poland are usually composed of the spined loach C. taenia Linnaeus, 1758 (2n=48) or the danubian loach C. elongatoides Bacescu & Maier, 1969 (2n=50), triploid hybrid females (3n=73, 3n=74, 3n=75) and tetraploid (4n=98, 4n=99) hybrids of both sexes. The results of our experimental studies reveal that c. 60% of eggs of allotriploid females dominating in these populations may be fertilized by C. taenia males whereas the tetraploid Cobitis males are sterile. The aim of this study was to show the chromosome structure of diploid and polyploid Cobitis males distributed in diploid and diploid-polyploid populations in Polish water bodies. Chromosomes of C. taenia and C. elongatoides males (each of 10 individuals) and of tetraploid Cobitis males (12 individuals) were examined using double-colour fluorescence in situ hybridisation (FISH) with 28S and 5S rDNA probes. In the karyotype of C. taenia and C. elongatoides respectively the modal number of nine and six, and seven and two, respectively of 28S rDNA and 5S rDNA sites were detected. C. taenia and C. elongatoides characterized respectively by four and two chromosomes containing hybridization sites of both rDNA probes (co-localizations). The chromosome sets of 4n males were composed of the C. taenia, C. elongatoides and C. tanaitica genomes. The pattern of rDNA sites distribution indicated that apart others the karyotypes of 4n males were composed of one or two haploid chromosome set of C. elongatoides. The presented data give an important insight into the structure of chromosomes of two Cobitis species and into the genome structure of allotetraploid Cobitis males. The obtained result is discussed with previously published studies.