BackgroundAmong Neotropical fishes, the family Characidae is highly diverse and speciose and its taxonomy is not completely resolved. In Chile, the family is represented by five species, all within the genus Cheirodon, of which C. pisciculus, C. galusdae, C. kiliani, and C. australe are endemic, while C. interruptus is introduced. We compared chromosomal markers in order to appreciate the taxonomy and evolution of these trans-Andean fishes.ResultsThe specimens were photographed in stereomicroscope to observe the ventral protrusive teeth and cusps for morphological analysis and species identification. All of the species analysed had equally diploid chromosome number 2n = 50, with karyotypes dominated by high number of acrocentric chromosomes as compared to those of other members of Cheirodontinae. The distribution of heterochromatin was inconspicuous and was similar in all the species. The number of active NORs (nucleolus organizer regions) was polymorphic, with the greater number of them in C. kiliani and C. galusdae. The location of 5S and 18S rDNA ranged in number and position, showing two sites in different chromosomes. The fluorescent in situ hybridization with telomeric probe did not reveal interstitial sites in all analysed species.ConclusionsThe comparative analysis of karyotypes and morphological markers revealed a biogeographic pattern of distribution, with the species that occur in the southern region forming one group and those in central and northern Chile forming another.

中文翻译：

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Cheirodon属（Teleostei：Characidae）跨安第斯特有鱼类的进化与染色体重排有关

背景在新热带鱼类中，Characidae 科具有高度多样性和特殊性，其分类学尚未完全解决。在智利，该科由五个物种代表，均属于 Cheirodon 属，其中 C. pisciculus、C. galusdae、C. kiliani 和 C. australe 是地方性的，而 C. interruptus 则被引入。我们比较了染色体标记，以了解这些跨安第斯鱼类的分类和进化。结果在体视显微镜下对标本进行拍照，观察腹侧突出的牙齿和尖端，以进行形态分析和物种鉴定。所分析的所有物种的二倍体染色体数量均相等，为 2n = 50，与 Cheirodontinae 的其他成员相比，核型以高数量的近着丝粒染色体为主。异染色质的分布不明显，在所有物种中均相似。活跃的 NOR（核仁组织区）的数量是多态的，在 C. kiliani 和 C. galusdae 中数量更多。5S 和 18S rDNA 的位置在数量和位置上不等，显示了不同染色体中的两个位点。端粒探针荧光原位杂交未显示所有分析物种的间隙位点。结论核型和形态标记的比较分析揭示了生物地理分布模式，发生在南部地区的物种形成一个组，中部和智利北部形成另一个。kiliani 和 C. galusdae。5S 和 18S rDNA 的位置在数量和位置上不等，显示了不同染色体中的两个位点。端粒探针荧光原位杂交未发现所有分析物种的间隙位点。结论核型和形态标记的比较分析揭示了生物地理分布模式，发生在南部地区的物种形成一个组，中部和智利北部形成另一个。kiliani 和 C. galusdae。5S 和 18S rDNA 的位置在数量和位置上不等，显示了不同染色体中的两个位点。端粒探针荧光原位杂交未显示所有分析物种的间隙位点。结论核型和形态标记的比较分析揭示了生物地理分布模式，发生在南部地区的物种形成一个组，中部和智利北部形成另一个。