The karyotype differentiation of the twelve known members of the Nothobranchius ugandensis Wildekamp, 1994 species group is reviewed and the karyotype composition of seven of its species is described herein for the first time using a conventional cytogenetic protocol. Changes in the architecture of eukaryotic genomes often have a major impact on processes underlying reproductive isolation, adaptation and diversification. African annual killifishes of the genus Nothobranchius Peters, 1868 (Teleostei: Nothobranchiidae), which are adapted to an extreme environment of ephemeral wetland pools in African savannahs, feature extensive karyotype evolution in small, isolated populations and thus are suitable models for studying the interplay between karyotype change and species evolution. The present investigation reveals a highly conserved diploid chromosome number (2n = 36) but a variable number of chromosomal arms (46–64) among members of the N. ugandensis species group, implying a significant role of pericentric inversions and/or other types of centromeric shift in the karyotype evolution of the group. When superimposed onto a phylogenetic tree based on molecular analyses of two mitochondrial genes the cytogenetic characteristics did not show any correlation with the phylogenetic relationships within the lineage. While karyotypes of many other Nothobranchius spp. studied to date diversified mainly via chromosome fusions and fissions, the N. ugandensis species group maintains stable 2n and the karyotype differentiation seems to be constrained to intrachromosomal rearrangements. Possible reasons for this difference in the trajectory of karyotype differentiation are discussed. While genetic drift seems to be a major factor in the fixation of chromosome rearrangements in Nothobranchius, future studies are needed to assess the impact of predicted multiple inversions on the genome evolution and species diversification within the N. ugandensis species group.

中文翻译：

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在系统发育和生物地理学的背景下，来自东非内陆高原的季节性鱼类——乌干达无鳃鱼物种组（Teleostei，Cyprinodontiformes）的核型分化

 回顾了 Nothobranchius ugandensis Wildekamp（1994 年物种组）12 个已知成员的核型分化，并首次使用常规细胞遗传学方案描述了其中 7 个物种的核型组成。真核基因组结构的变化通常对生殖隔离、适应和多样化的过程产生重大影响。非洲一年生鳉鱼属 Nothobranchius Peters, 1868（Teleostei：Nothobranchiidae）适应非洲大草原短暂湿地池的极端环境，在小而孤立的种群中具有广泛的核型进化特征，因此是研究之间相互作用的合适模型核型变化和物种进化。目前的研究揭示了乌干达猪笼草物种组成员中高度保守的二倍体染色体数量（2n = 36），但染色体臂的数量不同（46-64），这意味着着丝粒周倒位和/或其他类型的染色体倒位发挥了重要作用。群体核型进化中的着丝粒转移。当叠加到基于两个线粒体基因的分子分析的系统发育树上时，细胞遗传学特征没有显示出与谱系内的系统发育关系的任何相关性。而许多其他 Nothobranchius spp 的核型。迄今为止研究的多样化主要通过染色体融合和裂变，乌干达猪笼草物种组保持稳定的2n，并且核型分化似乎仅限于染色体内重排。讨论了核型分化轨迹中这种差异的可能原因。虽然遗传漂变似乎是 Nothobranchius 染色体重排固定的主要因素，但未来的研究需要评估预测的多重倒位对乌干达 N. ugandensis 物种组内基因组进化和物种多样化的影响。