Frontiers in Marine Science (Nov 2015)
Gene mapping of 28S and 5S rDNA sites in chromosomes of two Barbus species and their F1 hybrids (Teleostei, Cyprinidae)
Abstract
The genus Barbus is composed of 302 species possessing from 2n=50 to 3n = 150 chromosomes. The taxonomic status of some of them is still far from settled and some of them are of polyploid origin. Polyploid species may be a useful model system to comparatively investigate the evolutionary process along polyploidization at genome and chromosomal level and also because of their advantage to survive in different environmental conditions. At least three Barbus species (2n = 100) are distributed in Poland. The common barbel Barbus barbus (Linnaeus, 1758), and the carpathian barbel Barbus carpathicus Kotlík, Tsigenopoulos, Ráb & Berrebi, 2002 (= B. peloponnesius) are separated by a deep phylogenetic divergence. However, they represent similar habitat preferences. It is little know about the genetic architecture and evolutionary consequences of hybridization between B. barbus and B. carpathicus. Naturally occurring hybrids of both these species have been described morphologically by Rolik (1967). This work presents the results of gene mapping of 28S and 5S rDNA sites in the chromosomes of the common barbel females from Nysa Kłodzka River and the carpathian barbel males from the Dunajec River, and of their F1 hybrids (20 individuals). Kidneys were used to prepare chromosome slides using standard procedures (Boroń 1994). The location of ribosomal genes in the chromosomes is commonly used as very informative cytogenetic features. FISH with human 28S rDNA and loach 5S rDNA probes were used according to Fujiwara et al. (1998) and Boroń (2009). The 5S rDNA probe was labelled with biotin-16-dUTP and digoxigenin-11-dUTP using respectively, Biotin-Nick Translation and the DIG-Nick Translation Mix kits (Roche). The karyotypes of investigated hybrids and their parents, included 2n = 100 chromosomes. Variation of 28S rDNA was observed; from four to six in B. barbus and B. carphaticus, but most frequently six loci in B. barbus, and four loci in B. carphaticus, respectively have been detected. Variation, from two to eight of 28S rDNA sites in the chromosomes of hybrids was observed. The results with 5S rDNA probe gave an impression of more genomic stability, and 5S rDNA sites were located only on two chromosomes of all investigated species and their F1 hybrids. Simultaneous mapping of the two rDNA families on the chromosomes of all investigated individuals revealed that both 28S and 5S rDNA probes were located on different chromosomes. Chromosomal location of ribosomal DNA sequences is useful for comparative cytogenetic fish studies due to their relatively fast rate of evolution. The results of species from the family Barbinae comparatively presented here for the first time, and they may support further taxonomical studies of the Barbus species.
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