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Corresponding author: Eugene Krysanov ( krysanov@sevin.ru ) Academic editor: Inna Kuznetsova
© 2016 Eugene Krysanov, Tatiana Demidova, Bela Nagy.
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:
Krysanov E, Demidova T, Nagy B (2016) Divergent karyotypes of the annual killifish genus Nothobranchius (Cyprinodontiformes, Nothobranchiidae). Comparative Cytogenetics 10(3): 439-445. https://doi.org/10.3897/CompCytogen.v10i3.9863
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Karyotypes of two species of the African annual killifish genus Nothobranchius Peters, 1868, N. brieni Poll, 1938 and Nothobranchius sp. from Kasenga (D.R. Congo) are described. Both species displayed diploid chromosome number 2n = 49/50 for males and females respectively with multiple-sex chromosome system type X1X2Y/X1X1X2X2. The karyotypes of studied species are considerably different from those previously reported for the genus Nothobranchius and similar to the Actinopterygii conservative karyotype.
Africa, chromosome number, karyotype, killifish, Nothobranchius
Annual killifishes belonging to the genus Nothobranchius Peters, 1868 are mainly distributed in eastern Africa but several species are found in central Africa (
Killifishes of the genus Nothobranchius comprise 71 valid species (
A multiple-sex chromosome system of X1X1X2X2/X1X2Y type has been reported for only one species of Nothobranchius, N. guentheri (Pfeffer, 1893) with a female karyotype consisting of 36 chromosomes and the male karyotype consisting of 35 chromosomes (
In this paper, the karyotypes of two species, Nothobranchius brieni Poll, 1938 and Nothobranchius sp. from Kasenga, were studied, bringing the number of species studied to 25.
Specimens of N. brieni were collected from a large ephemeral swamp in the Lualaba drainage, near the village of Bukama in Katanga province (Democratic Republic of Congo, 09°11.374'S 25°51.334'E) on 2 April 2013 by E. Abwe, B. Katemo Manda, and B. Nagy, whereas specimens of Nothobranchius sp. from Kasenga (Nothobranchius sp. ‘Kasenga’) were collected in an ephemeral swamp in the Luapula drainage, near Kasenga, a village in Katanga province (D.R. Congo, 10°31.360'S, 28°27.368'E) on 17 April 2015, by E. Abwe, A. Chocha Manda, B. Katemo Manda, and T. Popp (Fig.
Localities of specimen collections in the Democratic Republic of Congo (1 Nothobranchius brieni 2 Nothobranchius sp. ‘Kasenga’).
Chromosomes were prepared according to the Kligerman and Bloom method (1974). The chromosome preparations were obtained from head kidney tissue. Before preparation fish were treated intraperitoneally with 0.1% colchicine for 3–4 hours. The hypotonisation lasted 20–30 min at room temperature in 0.075 M KCl. Then tissue samples were fixed in 3:1 methanol : acetic acid for 24 hours. Six specimens of N. brieni (three males and three females) and three specimens of Nothobranchius sp. ‘Kasenga’ (one male and three females) were karyotyped with this method. Meiotic chromosome preparations of N. brieni were acquired from testes by the same technique.
Slides were dried by air and stained with 2% Giemsa solution in phosphate buffer at pH 6.8 for 10 min. Karyotypes were analysed under microscope “AxioImager” Karl Zeiss (Germany) equipped with CCD camera and “KaryoImage” Metasystems Software (Germany). In each specimen the chromosome number and type was determined on metaphase plate. Chromosome morphology was determined according to
The diploid chromosome numbers of N. brieni were 2n = 49 for males and 2n = 50 for females with NF = 50/50 respectively. The female karyotype consisted of 25 pairs of acrocentric chromosomes gradually decreasing in size (Fig.
Karyotypes of Nothobranchius brieni a somatic chromosomes of female b somatic chromosomes of male c meiotic metaphase I (testicular). (A – acrocentric chromosomes). Note trivalent chromosome (arrowed). Scale bar: 10 µm.
The karyotype Nothobranchius sp. ‘Kasenga’ had diploid number 2n = 49 for males and 2n = 50 for females with NF = 68/68 respectively. The female karyotype had two pairs of metacentric, seven pairs of sub-metacentric, and 16 pair of acrocentric chromosomes varying in size from large to small (Fig.
The described karyotypes stand apart from those already reported for species of genus Nothobranchius. The karyotype of N. brieni has the chromosomal number 2n = 49/50 and 25 pairs of uni-armed chromosomes in female (50A) and 23 pairs of uni-armed homomorphic and three heteromorphic chromosomes in male (1M + 48A). The karyotype of Nothobranchius sp. ‘Kasenga’ has the same diploid number 2n = 49/50 but a different karyotype structure possessing metacentric, sub-metacentric, and uni-armed chromosomes with 4M + 14SM + 32A for females and 5M + 14SM + 30A for males, while other species of the genus have a considerably lower modal diploid number of only 36 chromosomes (Table
The diploid number (2n) of Nothobranchius species (from
Species | 2n | References |
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N. brieni Poll, 1938* | 49♂/50♀ | Current study |
N. eggersi Seegers, 1982 | 36 |
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N. elongatus Wildekamp, 1982 | 38 |
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N. foerschi Wildekamp & Berkenkamp, 1979 | 34 |
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N. furzeri Jubb, 1971 | 38 | Reichwald et al. 2009 |
N. guentheri (Pfeffer, 1893)* | 35♂/36♀ |
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N. hengstleri Valdesalici, 2007 | 38 |
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N. janpapi Wildekamp, 1977 | 38 |
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N. jubbi Wildekamp & Berkenkamp, 1979 | 34 |
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N. kirki Jubb, 1969 | 36 |
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N. korthausae Meinken, 1973 | 36 |
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N. krysanovi Shidlovskiy, Watters & Wildekamp, 2010 | 18 |
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N. kuhntae (Ahl, 1926) | 38 |
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N. lucius Shidlovskiy, Watters & Wildekamp, 2010 | 36 |
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N. makondorum Shidlovskiy, Watters & Wildekamp, 2010 | 38 |
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N. melanospilus (Pfeffer, 1896) | 38 |
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N. microlepis (Vinciguerra, 1897) | 24 |
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N. palmqvisti (Lönnberg, 1907) | 36 |
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N. polli Wildekamp, 1978 | 36 |
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N. patrizii (Vinciguerra, 1897) | 36 |
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N. pienaari Shidlovskiy, Watters & Wildekamp, 2010 | 34 |
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N. rachovii Ahl, 1926 | 16 |
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N. steinforti Wildekamp, 1977 | 36 |
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N. thierryi (Ahl, 1924) | 43 |
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Nothobranchius sp. ‘Kasenga’* | 49♂/50♀ | Current study |
The reduced diploid numbers and heteromorphic chromosomes in males suggest the occurrence of a multiple-sex chromosome system. A trivalent observation in the first meiotic chromosomes in N. brieni and the presence of a bi-armed chromosome exclusively in the male karyotype indicate a multiple-sex chromosome system of the type X1X2Y/X1X1X2X2. One bi-armed neo-Y chromosome has most likely resulted from the Robertsonian fusion between the Y chromosome and an autosome, as has been described for other fish species (e.g.,
In the genus Nothobranchius and the related Aphyosemyon Mayers, 1924 the evolutionary trend to reduce the total number of chromosomes via acrocentric chromosome fusion was specified (
This research work was supported by RFBR (Russian Foundation for Basic Research) #16-04-01102.