Comparative cytogenetic mapping of rRNA genes among naked catfishes: implications for genomic evolution in the Bagridae family

Abstract

ABSTRACT. In the present study, the karyotype and chromosomal characteristics of 9 species of the Bagridae fish family were investigated using conventional Giemsa staining as well as dual-color fluorescence in situ hybridization to detect the 18S and 5S rDNA sites. In addition to describing the karyotype of several Bagridae catfishes, we established molecular cytogenetic techniques to study this group. The 9 species contained a diploid chromosomal number, varying from 50 (Pseudomystus siamensis) to 62 (Hemibagrus wyckii), while none contained heteromorphic sex chromosomes. 18S rDNA sites were detected in only 1 chromosomal pair among all species evaluated. However, 3 different patterns were observed for the distribution of the 5S rDNA: 2 sites were found in the genus Mystus and in P. siamensis, multiple sites were observed in the genus Hemibagrus, and a syntenic condition for the 18S and 5S rDNA sites was identified in H. wyckii. The extensive variation in the number and chromosomal position of rDNA clusters observed among these Bagridae species may be related to the intense evolutionary dynamics of rDNA-repeated units, which generates divergent chromosomal distribution patterns even among closely related species. In summary, the distribution of repetitive DNA sequences provided novel, useful information regarding the evolutionary relationships between Bagridae fishes.

Nucleolar Organizer Regions Polymorphism and Karyological Analysis of Black Lancer, <i>Bagrichthys majusculus</i> (Siluriformes, Bagridae) in Thailand

“…All investigated specimens had no distinguishable sex chromosome. This characteristic is similar to other species in the Bagridae of Thailand (Donsakul 2001, Magtoon and Donsakul 2009, Supiwong et al2013a, b, 2014a. However, some bagrid catfishes in India, including M. gulio and M. tengara have differentiated sex chromosome system as XX/XY and ZZ/ZW, respectively (Rishi 1973, Rishi and Rishi 1981, Choudhury et al 1993, Arai 2011.…”

“…This is accordance with the previous studies of Magtoon and Arai (1988) and Donsakul (2002). However, the 2n is different from other species of the Bagridae (Barat and Khuda-Bukhsh 1986, Sharma and Tripathi 1986, Yu et al1989, Lakra and Rishi 1991, Khuda-Bukhsh et al 1995, Donsakul 2001, Das and Khuda-Bukhsh 2007a, Supiwong et al2013a, 2014a. The NF of B. majusculus was 96 in both males and females.…”

A Discovery of Nucleolar Organizer Regions (NORs) Polymorphism and Karyological Analysis of Crystal Eye Catfish, <i>Hemibagrus wyckii</i> (Siluriformes, Bagridae) in Thailand

“…Moreover, the 2n intra- specific variations were also found in several species such as H. menoda, 2n= 48 (Lakra and Rishi 1991), 2n= 58 (Das and Khuda-Bukhsh 2007a); H. nemurus, 2n= 56 Tripathi 1986Khuda-Bukhsh et al 1995), 2n= 58 (Barat and Khuda-Bukhsh 1986) and H. wyckii, 2n= 54 (Magtoon and Arai 1988), and 2n= 62 (Donsakul 2001, Supiwong et al 2014a, 2014b. Although there are few reports on fluorescence in situ hybridization (FISH) technique using ribosomal RNA genes, some microsatellites and repetitive DNA sequences mapping to the Bagridae fish chromosomes (Supiwong et al 2013a(Supiwong et al , 2014a(Supiwong et al , 2014b, the Ag-NOR banding in this Hemibagrus has not been reported. In the present article, our goal is to indicate the first finding of NOR polymorphism and chromosome analysis in the H. wyckii from Thailand, using conventional staining and Ag-NOR banding techniques.…”

“…Up to the present, only eight species of the genus Hemibagrus have been cytogenetically analyzed presenting the diploid chromosome number (2n) ranging from 48 chromosomes in H. menoda (Lakra and Rishi 1991) to 62 chromosomes in H. wyckii (Donsakul 2001, Supiwong et al 2014a, 2014b. Moreover, the 2n intra- specific variations were also found in several species such as H. menoda, 2n= 48 (Lakra and Rishi 1991), 2n= 58 (Das and Khuda-Bukhsh 2007a); H. nemurus, 2n= 56 Tripathi 1986Khuda-Bukhsh et al 1995), 2n= 58 (Barat and Khuda-Bukhsh 1986) and H. wyckii, 2n= 54 (Magtoon and Arai 1988), and 2n= 62 (Donsakul 2001, Supiwong et al 2014a, 2014b.…”

“…Up to the present, only eight species of the genus Hemibagrus have been cytogenetically analyzed presenting the diploid chromosome number (2n) ranging from 48 chromosomes in H. menoda (Lakra and Rishi 1991) to 62 chromosomes in H. wyckii (Donsakul 2001, Supiwong et al 2014a, 2014b. Moreover, the 2n intra- specific variations were also found in several species such as H. menoda, 2n= 48 (Lakra and Rishi 1991), 2n= 58 (Das and Khuda-Bukhsh 2007a); H. nemurus, 2n= 56 Tripathi 1986Khuda-Bukhsh et al 1995), 2n= 58 (Barat and Khuda-Bukhsh 1986) and H. wyckii, 2n= 54 (Magtoon and Arai 1988), and 2n= 62 (Donsakul 2001, Supiwong et al 2014a, 2014b. Although there are few reports on fluorescence in situ hybridization (FISH) technique using ribosomal RNA genes, some microsatellites and repetitive DNA sequences mapping to the Bagridae fish chromosomes (Supiwong et al 2013a(Supiwong et al , 2014a(Supiwong et al , 2014b, the Ag-NOR banding in this Hemibagrus has not been reported.…”