Karyotypic stasis and its implications for extensive hybridization events in corallivores species of butterflyfishes (Chaetodontidae).

The butterflyfishes (Chaetodontidae), emblematic inhabitants of coral reef environments, encompass the majority of known coralivorous species and show one of the highest hybridization rates known among vertebrates, making them an important evolutionary model. The vast knowledge about their life history and phylogenetic relationships contrasts with scarce information on their karyotype evolution. Aiming to expand the cytogenetic data of butterflyfishes and evaluate their karyotype evolution in association with evolutionary aspects, we conducted an extensive cytogenetic analysis in 20 species (Heniochus pleurotaenia and 19 Chaetodon spp.) from the Atlantic and Indo-Pacific regions, comparing the karyotype macrostructure and the arrangement of the 18S and 5S rDNA repetitive DNA classes in their chromosomes. The results demonstrate that butterflyfishes underwent a period of karyotypic stasis, as evidenced by their homoploid and structurally identical basal karyotype, which has 2n = 48 acrocentric chromosomes and is shared by 90% of species. Only C. trifascialis (2n = 48; FN = 50) and C. andamanensis (2n = 48; FN = 52) stood out because they both had karyotypes that diverged due to pericentric inversions. The microstructural arrays of 18S rDNA and 5S rDNA sequences were primarily comprised by single and independent loci on homologous chromosomes, indicating that there was little reshuffling among sets of orthologue chromosomes of species. Geographical comparisons revealed similar karyotypes between individuals of C. striatus from the Greater Caribbean and those of the coast of Brazil, corroborating previous data of gene flow through Amazon/Orinoco plume. The conservative chromosomal patterns in the butterflyfishes, likely overcome the limitations related to segregation and pairing of heterospecific complements and reinforce their contribution to the high degree of hybrid viability and introgression in Chaetodon species.

Chromosomes of Asian cyprinid fishes: Novel insight into the chromosomal evolution of Labeoninae (Teleostei, Cyprinidae).

The Labeoninae subfamily is a highly diversified but demonstrably monophyletic lineage of cyprinid fishes comprising five tribes and six incertae sedis genera. This widely distributed assemblage contains some 48 genera and around 480 recognized species distributed in freshwaters of Africa and Asia. In this study, the karyotypes and other chromosomal properties of five Labeoninae species found in Thailand Labeo chrysophekadion (Labeonini) and Epalzeorhynchos bicolor, Epalzeorhynchos munense, Henicorhynchus siamensis, Thynnichthys thynnoides (´Osteochilini´) were examined using conventional and molecular cytogenetic protocols. Our results confirmed a diploid chromosome number (2n) invariably 2n = 50, but the ratio of uni- and bi-armed chromosomes was highly variable among their karyotypes, indicating extensive structural chromosomal rearrangements. Karyotype of L. chrysophekadion contained 10m+6sm+20st+14a, 32m+10sm+8st for H. siamensis, 20m+12sm+10st+8a in E. bicolor, 20m+8sm+8st+14a in E. munense, and 18m+24sm+8st in T. thynnoides. Except for H. siamensis, which had four sites of 5S rDNA sites, other species under study had only one chromosome pair with those sites. In contrast, only one pair containing 18S rDNA sites were found in the karyotypes of three species, whereas two sites were found in that of E. bicolor. These cytogenetic patterns indicated that the cytogenomic divergence patterns of these labeonine species largely corresponded to the inferred phylogenetic tree. In spite of the 2n stability, diverse patterns of rDNA and microsatellite distribution as well as their various karyotype structures demonstrated significant evolutionary differentiation of Labeoninae genomes as exemplified in examined species. Labeoninae offers a traditional point of view on the evolutionary forces fostering biological diversity, and the recent findings add new pieces to comprehend the function of structural chromosomal rearrangements in adaption and speciation.

A comparative cytogenetic study of Hypsibarbusmalcolmi and H.wetmorei (Cyprinidae, Poropuntiini).

Cyprininae are a highly diversified but demonstrably monophyletic lineage of cypriniform fishes. Here, the karyotype and chromosomal characteristics of Hypsibarbusmalcolmi (Smith, 1945) and H.wetmorei (Smith, 1931) were examined using conventional, nucleolus organizing regions (NORs) and molecular cytogenetic protocols. The diploid chromosome number (2n) of H.malcolmi was 50, the fundamental number (FN) was equal to 62, and the karyotype displayed 8m + 4sm + 38a with NORs located at the centromeric and telomeric positions of the short arms of chromosome pairs 1 and 2, respectively. 2n of H.wetmorei was 50, FN 78, karyotype 14m + 14sm + 22a with the NORs at the telomeric position of the short arm of chromosome pair 2. 2n and FN in males and females were identical. Fluorescence in situ hybridization using different microsatellite motifs as probes also showed substantial genomic divergence between both studied species. In H.wetmorei, (CAG)n and (CAC)n microsatellites accumulated in the telomeric regions of all chromosomes, while in H.malcolmi, they had scattered signals on all chromosomes. Besides, the (GAA)n microsatellites were distributed along all chromosomes of H.malcolmi, but there was a strong hybridization pattern in the centromeric region of a single pair in H.wetmorei. These cytogenomic difference across the genomes of these Hypsibarbus Rainboth, 1996 species are markers for specific evolutionary differentiation within these two species.

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

The representatives of cyprinid lineage 'Poropuntiinae' with 16 recognized genera and around 100 species form a significant part of Southeast Asian ichthyofauna. Cytogenetics are valuable when studying fish evolution, especially the dynamics of repetitive DNAs, such as ribosomal DNAs (5S and 18S) and microsatellites, that can vary between species. Here, karyotypes of seven 'poropuntiin' species, namely Cosmochilus harmandi, Cyclocheilichthys apogon, Hypsibarbus malcomi, H. wetmorei, Mystacoleucus chilopterus, M. ectypus, and Puntioplties proctozysron occurring in Thailand were examined using conventional and molecular cytogenetic protocols. Variable numbers of uni- and bi-armed chromosomes indicated widespread chromosome rearrangements with a stable diploid chromosome number (2n) of 50. Examination with fluorescence in situ hybridization using major and minor ribosomal probes showed that Cosmochilus harmandi, Cyclocheilichthys apogon, and Puntioplites proctozystron all had one chromosomal pair with 5S rDNA sites. However, more than two sites were found in Hypsibarbus malcolmi, H. wetmorei, Mystacoleucus chilopterus, and M. ectypus. The number of chromosomes with 18S rDNA sites varied amongst their karyotypes from one to three; additionally, comparative genomic hybridization and microsatellite patterns varied among species. Our results reinforce the trend of chromosomal evolution in cyprinifom fishes, with major chromosomal rearrangements, while conserving their 2n.