Evolutionary analysis of genus Channa based on karyological and 16S rRNA sequence data

A wide range of diploid number of chromosomes and the body size of Channa congeners are useful combination of characters for studying the factors controlling the body size. In this study, the karyological information was superimposed on the evolutionary tree generated by 16S rRNA mitochondrial gene sequences. Here, the metaphase chromosome complements stained with Giemsa, AgNO₃ and CMA₃ were prepared from six snakehead murrel fish species collected from northeast India. The diploid chromosome numbers and the fundamental arms of C. aurantimaculata (2n = 52, NF = 98), C. gachua (2n = 56, NF = 84), C. marulius (2n = 44, NF = 58), C. orientalis (2n = 52, NF = 74), C. punctata (2n = 32, NF = 60) and C. striata (2n = 40, NF = 48) were calculated by the analysis of metaphase chromosome complements. Both methods of nucleolar organizer region (NOR) localization, silver nitrate and chromomycin A₃, revealed NOR pairs of 1, 2, 3, 1, 4 and 3 in C. aurantimaculata, C. gachua, C. marulius, C. orientalis, C. punctata and C. striata, respectively. The subject species showed primitive type of asymmetrical chromosomes, except the C. punctata. The variation in 2n for C. orientalis (2n = 52, 78) and C. gachua (2n = 52, 78, 104) of a complete haploid set indicates the possibility of either ploidy change in C. orientalis and C. gachua, if we consider 2n = 52 or the Robertsonian rearrangements in different populations of these two species. The chromosome evolution tree was constructed on 16S rRNA ML-phylogenetic tree using ChromEvol 1.3. The analysis of chromosome evolution explained the loss or gain of chromosome, duplications or semiduplications mechanism. For time scaling the chromosomeevolution, the node age of available 16S rRNA gene of Channa species were estimated, which was also used for estimating the time when chromosomal changes occurred in context of geological time-scale.