Although crocodilians have attracted enormous attention in other research fields, from the cytogenetic point of view, this group remains understudied. Here, we analyzed the karyotypes of eight species formally described from the Alligatoridae family using differential staining, fluorescence in situ hybridization with rDNA and repetitive motifs as a probe, whole chromosome painting (WCP), and comparative genome hybridization. All Caimaninae species have a diploid chromosome number (2n) 42 and karyotypes dominated by acrocentric chromosomes, in contrast to both species of Alligatorinae, which have 2n = 32 and karyotypes that are predominantly metacentric, suggesting fusion/fission rearrangements. Our WCP results supported this scenario by revealing the homeology of the largest metacentric pair present in both Alligator spp. with two smaller pairs of acrocentrics in Caimaninae species. The clusters of 18S rDNA were found on one chromosome pair in all species, except for Paleosuchus spp., which possessed three chromosome pairs bearing these sites. Similarly, comparative genomic hybridization demonstrated an advanced stage of sequence divergence among the caiman genomes, with Paleosuchus standing out as the most divergent. Thus, although Alligatoridae exhibited rather low species diversity and some level of karyotype stasis, their genomic content indicates that they are not as conserved as previously thought. These new data deepen the discussion of cytotaxonomy in this family.

Alfred Nobel Strasse 1e 55411 Bingen am Rhein Germany

An der Nachtweide 16 60433 Frankfurt Germany

Department of Ecology Faculty of Science Charles University 12844 Prague Czech Republic

Institute for Applied Ecology Faculty of Science and Technology University of Canberra Bruce ACT 2617 Australia

Institute of Human Genetics Jena University Hospital Am Klinikum 1 07747 Jena Germany

Laboratório de Citogenética de Peixes Departamento de Genética e Evolução Universidade Federal de São Carlos São Carlos 13565 905 Brazil

Laboratório de Genética Animal Coordenação de Biodiversidade Instituto Nacional de Pesquisas da Amazônia Manaus 69083 000 Brazil

Laboratory of Fish Genetics Institute of Animal Physiology and Genetics Czech Academy of Sciences 27721 Liběchov Czech Republic

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