Comparative karyotypic study of fifteen cyprinids (Cyprinidae, Cyprininae) species. An insight into the chromosomal evolution of the tribe Systomini.

The family Cyprinidae is the largest freshwater fish group with 377 genera and over 3,000 described species. However, this group of fish has very limited cytogenetics and advanced molecular cytogenetics information. Therefore, in this study the karyotypes and other chromosomal characteristics of 15 species in the tribe Systomini (Cyprininae) were examined using Ag-NOR staining along with fluorescence in situ hybridization (5S and 18S rDNA). All species share a similar karyotype (2n = 50; NF = 88-100) in both sexes and no differentiated sex chromosome was observed. Chromosomes bearing NOR sites ranged from one to four pairs among the species, mostly mapped adjacent to telomeres in the short arms of distinct pairs in all analyzed species. This difference indicates an extensive rearrangement of chromosomes including genomic differences. The use of the 5S and 18S rDNA probe confirmed the Ag-NOR sites interstitially located in the telomeric regions of distinct chromosomes, characterizing an interspecies variation of these sites. In most of its analyzed species, the signals of 18S rDNA probe corresponded to the Ag-NOR regions, except in Barbonymus altus, B. gonionotus, B. schwanenfeldii and Puntius brevis having these signals on the same as Ag-NOR regions and other sites.

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.

Comparative study of four Mystus species (Bagridae, Siluriformes) from Thailand: insights into their karyotypic diversity.

Karyotypes of four catfishes of the genus Mystus Scopoli, 1777 (family Bagridae), M. atrifasciatus Fowler, 1937, M. mysticetus Roberts, 1992, M. singaringan (Bleeker, 1846) and M. wolffii (Bleeker, 1851), were analysed by conventional and Ag-NOR banding as well as fluorescence in situ hybridization (FISH) techniques. Microsatellite d(GC)15, d(CAA)10, d(CAT)10 and d(GAA)10 repeat probes were applied in FISH. The obtained data revealed that the four studied species have different chromosome complements. The diploid chromosome numbers (2n) and the fundamental numbers (NF) range between 52 and 102, 54 and 104, 56 and 98, or 58 and 108 in M. mysticetus, M. atrifasciatus, M. singaringan or M. wolffii, respectively. Karyotype formulae of M. mysticetus, M. atrifasciatus, M. singaringan and M. wolffii are 24m+26sm+4a, 26m+24sm+2a, 24m+18sm+14a and 30m+22sm+6a, respectively. A single pair of NORs was identified adjacent to the telomeres of the short arm of chromosome pairs 3 (metacentric) in M. atrifasciatus, 20 (submetacentric) in M. mysticetus, 15 (submetacentric) in M. singaringan, and 5 (metacentric) in M. wolffii. The d(GC)15, d(CAA)10, d(CAT)10 and d(GAA)10 repeats were abundantly distributed in species-specific patterns. Overall, we present a comparison of cytogenetic and molecular cytogenetic patterns of four species from genus Mystus providing insights into their karyotype diversity in the genus.