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.
Highlights
The genomes of teleost fishes display remarkable features that might be involved in the formation of their immense species diversity.Access to whole-genome sequences provides important insights into the gene occurrence and organisation within a species, and it revolutionises our understanding of how genetic information isGenes 2020, 11, 818; doi:10.3390/genes11070818 www.mdpi.com/journal/genesGenes 2020, 11, 818 stored and organised in DNA molecules and chromosomes and how it evolved over time
We examined Running River rainbowfish (Melanotaenia sp.), red rainbowfish (Glossolepis incisus), threadfin rainbowfish (Iriatherina werneri), ornate rainbowfish (Rhadinocentrus ornatus), and Cairns rainbowfish (Cairnsichthys rhombosomoides)
More information about themales number offrom cells isWild listed in Table obtained under state fishery permits, and fish research was conducted with approval the University of females from rhombosomoides
Summary
The genomes of teleost fishes display remarkable features (e.g., variability in size or basic chromosome organisation) that might be involved in the formation of their immense species diversity. Three of the more distantly related genera (Cairnsichthys, Rhadinocentrus, and Iriatherina) were not found to hybridise in wild populations, despite often sharing habitats with another rainbowfish species. This suggests that divergent chromosomal evolution may be playing a role of the postzygotic barrier in hybridisation events (as shown in, e.g., Molina et al [13]). We focused on representatives of five main phylogenetic lineages among rainbowfishes to cover trends in chromosome and genome organisation in this group. Wild samples were five males and captive population from two males two three males three females of incisus
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