Cytogenetics of two hylid frogs from Brazilian Cerrado

Abstract Cytogenetic data can be useful for taxonomic and phylogenetic studies, as well as to provide information about chromosome evolution. Therefore, it may help design conservation priorities for some threatened species, such as anurans. Herein, we describe the karyotypes of Scinax constrictus and Ololygon centralis, native endemic species from the Brazilian Cerrado. Chromosome preparations for both species were stained with Giemsa for morphological analyses and then impregnated by the Ag-NOR method for localization of the nucleolar organizer region (NOR). Both species had 24 chromosomes, as confirmed by meiotic analyses, which showed 12 bivalents. Chromosome morphologies presented the same pattern for Scinax and Ololygon compared to species already karyotyped in both genera. The NOR was interstitially located in the long arm of pair 7 in S. constrictus, whereas in O. centralis it was found near the centromere in the long arm of pair 1, thus diverging from what is commonly found for other Ololygon species. Therefore, we provide the first description of the karyotype of O. centralis and the first report of the localization of the NOR for the karyotype of both species. Our study increases the cytogenetic knowledge in species of the genera Scinax and Ololygon, and provide support for further studies on the taxonomy, ecology, and evolution of hylid anurans.

摘要 细胞遗传学数据可应用于分类学与系统发育研究，同时可为染色体演化相关研究提供关键信息。因此，这类数据可辅助确定部分受威胁物种（如无尾类）的保护优先级。本研究针对巴西塞拉多的特有本土物种Scinax constrictus与Ololygon centralis，对其核型进行了详细描述。针对两个物种的染色体制片，均采用吉姆萨（Giemsa）染色开展形态学分析，随后通过银染核仁组织者区（Ag-NOR）法完成核仁组织者区（nucleolar organizer region, NOR）的定位。经减数分裂分析验证，两个物种的染色体数目均为24条，可观察到12个二价体。相较于两属中已完成核型鉴定的物种，Scinax属与Ololygon属的染色体形态模式一致。Scinax constrictus的NOR位于第7号染色体长臂的居间区域；而Ololygon centralis的NOR则位于第1号染色体长臂的着丝粒附近，这与其他Ololygon属物种的常见定位模式存在差异。因此，本研究首次报道了Ololygon centralis的核型，以及两个物种核型中NOR的定位情况。本研究丰富了Scinax属与Ololygon属物种的细胞遗传学认知，并为雨蛙科无尾类的分类学、生态学及演化相关后续研究提供了理论支撑。