Evidence of Interspecific Chromosomal Diversification in Rainbowfishes (Melanotaeniidae, Teleostei)

Abstract

Rainbowfishes (Melanotaeniidae) are the largest monophyletic group of freshwater fishes occurring in Australia and New Guinea, with 112 species currently recognised. Despite their high taxonomic diversity, rainbowfishes remain poorly studied from a cytogenetic perspective. Using conventional (Giemsa staining, C banding, chromomycin A3 staining) and molecular (fluorescence in situ hybridisation with ribosomal DNA (rDNA) and telomeric probes) cytogenetic protocols, karyotypes and associated chromosomal characteristics of five species were examined. We covered all major lineages of this group, namely, Running River rainbowfish Melanotaenia sp., red rainbowfish Glossolepis incisus, threadfin rainbowfish Iriatherina werneri, ornate rainbowfish Rhadinocentrus ornatus, and Cairns rainbowfish Cairnsichthys rhombosomoides. All species had conserved diploid chromosome numbers 2n = 48, but karyotypes differed among species; while Melanotaenia sp., G. incisus, and I. werneri possessed karyotypes composed of exclusively subtelo/acrocentric chromosomes, the karyotype of R. ornatus displayed six pairs of submetacentric and 18 pairs of subtelo/acrocentric chromosomes, while C. rhombosomoides possessed a karyotype composed of four pairs of submetacentric and 20 pairs of subtelo/acrocentric chromosomes. No heteromorphic sex chromosomes were detected using conventional cytogenetic techniques. Our data indicate a conserved 2n in Melanotaeniidae, but morphologically variable karyotypes, rDNA sites, and heterochromatin distributions. Differences were observed especially in taxonomically divergent species, suggesting interspecies chromosome rearrangements.

Present and Future Salmonid Cytogenetics

“…In our study, we observed the variability in the size of the NOR-bearing p arm of this marker chromosome corresponding to the 28S rDNA signal, similar to Caputo et al [28] in S. marmoratus. The intraspecific variability of the 5S rDNA cytotaxonomic marker is quite well known [85][86][87]. Surprisingly, the location of 5S rDNA genes in the genus Salmo was examined in two studies only.…”

Chromosomes of Asian Cyprinid Fishes: Genomic Differences in Conserved Karyotypes of ‘Poropuntiinae’ (Teleostei, Cyprinidae)

“…The abundance and the chromosomal location of the repetitive DNA fraction change significantly between genomes of closely related species, and these variations are generally species-specific [ 17 ]. In this context, comparative genomic hybridization (CGH) and fluorescence in situ hybridization (FISH) mapping of repetitive DNAs were extensively used in teleost chromosomal research [ 18 , 19 , 20 , 21 , 22 , 23 ]. Ribosomal DNAs, for example, were frequently mapped in fish genomes and have been shown to occur mostly in separated chromosomes, though syntenic association has been reported in some species.…”