Abstract
Crocodilians have maintained very similar karyotype structures and diploid chromosome numbers for around 100 million years, with only minor variations in collinearity. Why this karyotype structure has largely stayed unaltered for so long is unclear. In this study, we analyzed the karyotypes of six species belonging to the genera Crocodylus and Osteolaemus (Crocodylidae, true crocodiles), among which the Congolian endemic O. osborni was included and investigated. We utilized various techniques (differential staining, fluorescence in situ hybridization with repetitive DNA and rDNA probes, whole chromosome painting, and comparative genomic hybridization) to better understand how crocodile chromosomes evolved. We studied representatives of three of the four main diploid chromosome numbers found in crocodiles (2n = 30/32/38). Our data provided new information about the species studied, including the identification of four major chromosomal rearrangements that occurred during the karyotype diversification process in crocodiles. These changes led to the current diploid chromosome numbers of 2n = 30 (fusion) and 2n = 38 (fissions), derived from the ancestral state of 2n = 32. The conserved cytogenetic tendency in crocodilians, where extant species keep near-ancestral state, contrasts with the more dynamic karyotype evolution seen in other major reptile groups.
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Acknowledgements
We would like to thank the private Crocodile Zoo Protivín (www.krokodylizoo.cz), namely Miroslav Procházka, for the samples of C. mindorensis and C. moreletii, Pilsen Zoo (www.zooplzen.cz), namely Tomáš Jirásek, for samples of O. tetraspis, “maman” Colette Uwonani Ambemane (Kinshasa) for helping us to access O. osborni, and Šárka Pelikánová for her help with the laboratory work.
Funding
V.C.S.O. was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brasil (CAPES) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (200401/2022–0). M.A. was supported by the Charles University Research Centre program 204069 and by the Czech Science Foundation Project No. 20-27236 J. V.G. was supported by the Czech Science Foundation (23-07331S), and the Ministry of Culture of the Czech Republic (DKRVO 2019–2023/6.VII.e, National Museum, 00023272). M.d.B.C. was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (302928/2021–9), Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (2020/11772–8). MBC and TL were supported by Alexander von Humboldt-Stiftung. We acknowledge support by the German Research Foundation Projekt-Nr. 512648189 and the Open Access Publication Fund of the Thueringer Universitaets- und Landesbibliothek Jena. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brasil (CAPES), Finance Code 001.
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V.C.S.O., M.A., V.G., R.K., and M.B.C wrote the main manuscript text; V.C.S.O., M.A., V.G., T.L., N.P., G.B., A.T., and M.B.C performed the sampling and the experiments; V.C.S.O., M.A T.E., T.L., R.U., and M.B.C. prepared the figures. All authors reviewed and approved the final version of the manuscript.
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Sup Fig. 1.
FISH with the vertebrate telomeric (TTAGGG)n probe in four representative species, namely a) Crocodylus rhombifer (2n=30), b) Crocodylus moreletii (2n=32), c) Osteolaemus osborni (2n=30) and d) Osteolaemus tetraspis (2n=38). Bar = 20 µm (PNG 519 kb)
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Sales-Oliveira, V., Altmanová, M., Gvoždík, V. et al. Cross-species chromosome painting and repetitive DNA mapping illuminate the karyotype evolution in true crocodiles (Crocodylidae). Chromosoma 132, 289–303 (2023). https://doi.org/10.1007/s00412-023-00806-6
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DOI: https://doi.org/10.1007/s00412-023-00806-6