Research Article |
Corresponding author: Denis V. Prazdnikov ( pdvfish3409@rambler.ru ) Academic editor: Ilya Gavrilov-Zimin
© 2023 Denis V. Prazdnikov.
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:
Prazdnikov DV (2023) Chromosome complements of Channa lucius and C. striata from Phu Quoc Island and karyotypic evolution in snakehead fishes (Actinopterygii, Channidae). Comparative Cytogenetics 17(1): 1-12. https://doi.org/10.3897/compcytogen.v17.i1.94943
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Snakehead fishes of the family Channidae are obligatory air-breathers freshwater predators, the vast majority of which belong to the genus Channa Scopoli, 1777. Channa species are characterized by high karyotypic diversity due to various types of chromosomal rearrangements. It is assumed that, in addition to the lifestyle, fragmentation and isolation of snakehead populations contribute to an increase in karyotypic diversity. However, the chromosome complements of many isolated populations of widespread Channa species remain unknown, and the direction of karyotype transformations is poorly understood. This paper describes the previously unstudied karyotypes of Channa lucius (Cuvier, 1831) and C. striata (Bloch, 1793) from Phu Quoc Island and analyzes the trends of karyotypic evolution in the genus Channa. In C. lucius, the karyotypes are differed in the number of chromosome arms (2n = 48, NF = 50 and 51), while in C. striata, the karyotypes are differed in the diploid chromosome number (2n = 44 and 43, NF = 48). A comparative cytogenetic analysis showed that the main trend of karyotypic evolution of Channa species is associated with a decrease in the number of chromosomes and an increase in the number of chromosome arms, mainly due to fusions and pericentric inversions. The data obtained support the assumption that fragmentation and isolation of populations, especially of continental islands, contribute to the karyotypic diversification of snakeheads and are of interest for further cytogenetic studies of Channidae.
Channa species, chromosomal rearrangements, karyotype differentiation, snakeheads
The family Channidae includes two genera of freshwater snakehead fishes (Parachanna Teugels et Daget, 1984 and Channa Scopoli, 1777) with a disjunct range (
Appearing in the Eocene, snakehead fishes have undergone a long evolution with multiple range expansions and repeated contacts with lineages that had diverged in isolation (
In the course of evolution, snakehead fishes developed accessory air-breathing organs, which allows them to do without water for a long time and migrate over land to colonize new habitats (
This study presents chromosome complements of C. lucius and C. striata from Phu Quoc Island and comparative cytogenetic analysis (chromosome number and karyotype composition) of the genus Channa. The trends in the karyotypic evolution of snakeheads and chromosomal diversification due to the isolation of island populations are discussed.
Individuals of Channa species were collected from Phu Quoc Island (Gulf of Thailand, Vietnam) (Fig.
Map showing the location of Phu Quoc Island (left) and island details with Channa species collection sites (right).
Chromosome preparations were obtained from the anterior part of the kidney according to previously published methods (
For C. lucius from both studied localities of Phu Quoc Island, the same diploid number of 2n = 48 was characteristic, but a different karyotype composition. In individuals from the Bai Dai River basin, the karyotype consisted of 2 metacentric chromosomes (m) and 46 subtelocentric and acrocentric chromosomes (st/a), NF = 50 (Fig.
Karyotypes of Channa lucius (A, B) and C. striata (C, D) from Phu Quoc Island. Numerals indicate the paired chromosomes. Scale bar: 5 μm.
Comparative analysis of island and mainland populations of C. lucius showed interpopulation chromosomal variability. Populations from Thailand and Phu Quoc Island differed in the number of m-chromosomes (Table
Diploid chromosome number (2n), chromosome arm number (NF), karyotype structure, and collection site of Channa lucius and C. striata.
Species | 2n | NF | Karyotype structure | Locality | References |
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C. lucius | 48 | 50 | 2m+46st/a | Northeastern Thailand (Bung Klua reservoir in the Roi-Et) |
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48 | 52 | 2m+2sm+2st+42a | Thailand |
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48 | 52 | 4m/sm/st+44a | Southern Thailand (Tapi Basin) |
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48 | 50 | 2m+46st/a | Vietnam (Phu Quoc Island, Bai Dai River Basin) | This study | |
48 | 51 | 3m+45st/a | Vietnam (Phu Quoc Island, Duong Dong River Basin) | This study | |
C. striata | 40 | 50 | 8m+2sm+2st+28a | India |
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40 | 48 | 8m+6st+26a | India (Assam, Meghalaya) |
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40 | 48 | 8m+2st+30a | India (Imphal) |
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40 | 50 | 8m+2sm+30st/a | India (WB) |
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40 | 58 | 8m+10sm+22a | India (Manipur) |
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40 | 48 | 6m+2sm+10st+22a | Northeastern India |
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42 | 48 | 6m+36st/a | Northeast Thailand (Khon Kaen, Mahasakam) |
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44 | 46 | 2m+42a | China | ||
43 | 50 | 7m/sm/st+36a | Northeastern Thailand (Chi Basin) |
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44 | 50 | 6m/sm/st+38a | Central and Southern Thailand (Chao Phraya Basin, Tapi Basin) |
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44 | 48 | 2m+2sm+40a | Thailand |
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44 | 48 | 2m+2sm+40st/a | Vietnam (Phu Quoc Island, Bai Dai River Basin) | This study | |
43 | 48 | 3m+2sm+38st/a | This study |
The probable maximum age of isolation of Phu Quoc Island from the Cambodian mainland is about ten thousand years when sea levels rose after the end of the last glacial period (
An analysis of cytogenetic data (
Phylogenetic tree of the cytogenetically studied Channa species (based on
Scatter plot of a diploid chromosome number and proportion of metacentric/submetacentric chromosomes (m/sm) with overall regression line for the genus Channa. The diameter and color of a circle indicate the number of species from 1 to 2.
The probable ancestral karyotype of snakeheads consisted of 48 uniarmed chromosomes, which would require a minimum number of chromosome rearrangements during the karyotype transformation of the number of Channa species. Among the cytogenetically studied species, C. argus and C. lucius have a karyotype with 2n = 48; the latter is also characterized by plesiomorphic features, such as the gular scales, which is absent in most species of Asian snakeheads (
The trends of karyotypic evolution for the genus Channa. The thick blue arrow shows the most likely main trend in karyotypic evolution. The lower rectangle shows the ancestral karyotype. fu – centric fusions, fiss – centric fissions, per inv – pericentric inversions, polypl – polyploidization.
Chromosomal rearrangements, which involve karyotypic structural changes such as inversions and fusions, may play an important role in the adaptive evolution of fish (
The proposed expansion of the ranges of modern taxa of Asian snakeheads at the Miocene/Pliocene boundary, combined with climatic fluctuations, led to repeated isolations of populations, especially continental islands, and secondary contacts between them (
I am grateful to the administration of the Vietnam-Russian Tropical Center for organizing and financially supporting field research on Phu Quoc Island.
Denis V. Prazdnikov https://orcid.org/0000-0003-0447-7431