Research Article |
Corresponding author: Weerayuth Supiwong ( supiwong@hotmail.com ) Academic editor: Sergey A. Simanovsky
© 2023 Sudarat Khensuwan, Weerayuth Supiwong, Chatmongkon Suwannapoom, Phichaya Buasriyot, Sitthisak Jantarat, Weera Thongnetr, Nawarat Muanglen, Puntivar Kaewmad, Pasakorn Saenjundaeng, Kriengkrai Seetapan, Thomas Liehr, Alongklod Tanomtong.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Khensuwan S, Supiwong W, Suwannapoom C, Buasriyot P, Jantarat S, Thongnetr W, Muanglen N, Kaewmad P, Saenjundaeng P, Seetapan K, Liehr T, Tanomtong A (2023) A comparative cytogenetic study of Hypsibarbus malcolmi and H. wetmorei (Cyprinidae, Poropuntiini). Comparative Cytogenetics 17: 181-194. https://doi.org/10.3897/compcytogen.17.107703
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Cyprininae are a highly diversified but demonstrably monophyletic lineage of cypriniform fishes. Here, the karyotype and chromosomal characteristics of Hypsibarbus malcolmi (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.
Fish cytogenetics, Cyprinidae, microsatellites, chromosomes
The Cyprininae are the largest subfamily of the family Cyprinidae, which are the most diverse group of freshwater fish worldwide. This subfamily currently includes 33 genera, with 228 species being widely distributed in the freshwater systems of Eurasia (
Collection sites of Hypsibarbus malcolmi (1) and H. wetmorei (2) in the Mekong River, North-East Thailand (18°17'48.2"N, 104°00'16.9"E and 18°17'59.9"N, 104°00'09.5"E). Scale bar for fish: 1 cm.
The diploid chromosome number of H. malcolmi and H. wetmorei has been reported as 2n = 50, but the karyotype and NF of H. malcolmi seem to be different (
Classical and molecular cytogenetics play a crucial role in elucidating evolutionary patterns in cyprinid fish, especially in cases when species exhibit conserved diploid numbers. The abundance and chromosomal location of specific repetitive DNAs (microsatellites) change significantly between genomes of closely related species, and these variations are generally species-specific (
The present study includes in-depth cytogenetic analyses of H. malcolmi and H. wetmorei (not a hybrid), comprising conventional Giemsa- and Ag-NOR staining and fluorescence in situ hybridization (FISH) approaches with chromosomal mapping of several repetitive DNA classes (microsatellites).
Individuals of H. malcolmi (12♂ and 6♀) and H. wetmorei (8♂ and 8♀) were collected in the Mekong River basin (Thailand) (Fig.
Mitotic chromosomes were obtained from the anterior kidney following the drop onto microscopic slides and the air-dry method to visualize the chromosomes (Bertollo 2015). Conventional staining was performed using 5% Giemsa for 8 min (
FISH experiments were performed under high stringency conditions (
At least 20 metaphase spreads per individual were analyzed to confirm the diploid number, karyotype structure, NORs and FISH data. Images were captured using an Axioplan II microscope (Carl Zeiss Jena GmbH, Germany) with CoolSNAP and processed using Image Pro Plus 4.1 software (Media Cybernetics, Silver Spring, MD, USA). Chromosomes were classified according to centromere position as metacentric (m), submetacentric (sm) and acrocentric (a) (
Cytogenetic analysis of H. malcolmi revealed 2n = 50 and FN = 62 in both sexes with a karyotype composed of 8 metacentric, 4 submetacentric and 38 acrocentric chromosomes (Fig.
Karyotypes after conventional Giemsa (A, B) and NOR staining (arrows) (C, D) of Hypsibarbus malcolmi, 2n = 50 (A, C) and H. wetmorei, 2n = 50 (B, D). Scale bar: 5 μm.
Species | 2n | FN | Karyotype | Locality | NORs site | References |
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Hypsibarbus lagleri Rainboth, 1996 | 50 | 74 | 4m + 20sm + 26a | Thailand | - | Donsakul et al. 2002 |
Hypsibarbus malcolmi (Smith, 1945) | 50 | 64 | 10m + 4sm + 36a | Thailand | - |
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50 | 62 | 8m + 4sm + 38a | Thailand | 1, 5 |
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50 | 62 | 8m + 4sm + 38a | Thailand | 1, 5 | Present study | |
Hypsibarbus vernayi (Norman, 1925) | 50 | 58 | 6m + 2sm + 4st + 38a | Thailand | - | Donsakul et al. 2002 |
Hypsibarbus wetmorei (Smith, 1931) | 50 | 70 | 12m + 8sm + 6st + 24a | Thailand | - |
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50 | 74 | 12m + 12sm + 4st + 22a | Thailand | 2 |
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50 | 74 | 12m + 12sm + 2st + 24a | Thailand | - | Donsakul et al. 2002 | |
50 | 82 | 10m + 14sm + 8st + 18a | Thailand | 6 |
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50 | 78 | 14m + 14sm + 22a | Thailand | 2 |
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50 | 78 | 14m + 14sm + 22a | Thailand | 2 | Present study |
While H. malcolmi had two pairs of NOR-bearing chromosomes, H. wetmorei had only one such pair. In the first, Ag-NOR regions were located at the centromeric and telomeric positions of the short arms on metacentric pairs 1 and 5 (Fig.
In H. wetmorei the (CAG)n and (CAC)n microsatellites accumulated in the telomeric regions of all chromosomes, while H. malcolmi had scattered signals along all 50 chromosomes. (GAA)n presented strong signals in the centromeric regions of a single chromosomal pair in H. malcolmi, but a scattered distribution among all chromosomes in H. wetmorei (Fig.
Our study has characterized populations of H. malcolmi and H. wetmorei by classical and molecular cytogenetics. For both species, diploid number and other features described in the scientific literature were confirmed (
The position of NOR was consistent with the previous report for both species, with two pairs in H. malcolmi and one in H. wetmorei. The occurrence of multiple NORs in fish was considered to be apomorphic, whereas a single pair of NORs is considered to be plesiomorphic (
The instability of repetitive regions of the genome can also be observed by microsatellites. These small repetitive motifs have been shown to stall and reverse replication forks, and to be hotspots of chromosomal double strand breaks in model organisms (
This study applied conventional and molecular cytogenetics to study the karyotypes and chromosomal characteristics of H. malcolmi and H. wetmorei. Both species present similar morphology and a conservative 2n = 50. However, they can be distinguished based on their chromosomal morphology, NORs sites and repetitive DNAs, such as (CAG)n, (GAA)n and (CAC)n, showed specificities in their distribution among species, thus being shown as good markers and promoters of specific genomic differentiation inside the genus.
This research project is supported by the National Research Council of Thailand (NCRT): NRCT-RGJ63003-068. The Thailand Science research and innovation fund and the University of Phayao (Grant No. FF66-UoE013). The Department of Biology, Faculty of Science, Khon Kaen University (KKU), Thailand. The Institute of Human Genetics, University Hospital Jena, Germany. The Departamento de Genética e Evolução Universidade Federal de São Carlos (UFSCar – SP). As well as for their helpful advice on this work.
Sudarat Khensuwan https://orcid.org/0009-0007-4019-5489
Weerayuth Supiwong https://orcid.org/0000-0002-1670-3224
Phichaya Buasriyot https://orcid.org/0000-0003-0821-7629
Thomas Liehr https://orcid.org/0000-0003-1672-3054
Alongklod Tanomtong https://orcid.org/0000-0002-8466-3594