The scorpion Tityus bahiensis is the most common scorpion species of medical importance with sexual reproduction in South America. Many of the populations cytogenetically studied so far are polymorphic both for chromosome number and meiotic configuration in males. In this work, we perform cytogenetic analysis of three of the most meridional populations of T. bahiensis occurring in north-eastern Argentina (Misiones province), which showed numerical and structural variations with respect to previously studied populations. We describe four new diploid numbers in males for this species, from 2n = 12 to 2n = 15, seven different cytotypes, and we analyze the chromosome rearrangements involved in the different multivalent associations observed during meiosis (II, III, V, VI, VII and IX). Ribosomal DNA is invariably present at one terminal region on each of two chromosomes. Blocks of constitutive heterochromatin of different sizes are found at the terminal regions of every chromosome in the different cytotypes, along with subterminal and interstitial blocks in some chromosomes. Based on the rDNA and constitutive heterochromatin localization, we analyzed chromosome evolution within these populations. We propose that all the cytotypes could have originated from a hypothetical ancestral karyotype with 2n = 18 and 9 bivalents at meiosis I but followed two pathways with different sequences of mainly fusions and some translocations from the ancestral karyotype. Furthermore, we review all the cytogenetically studied populations of this species and their distribution to discuss the chromosomal evolution of this polymorphic species.

蝎子Tityus bahiensis是南美洲最重要的具有性繁殖医学意义的蝎子。到目前为止，许多通过细胞遗传学研究的种群在男性的染色体数目和减数分裂构型上都是多态的。在这项工作中，我们对T. bahiensis的三个最经向种群进行细胞遗传学分析发生在阿根廷东北部（米西奥内斯省），该区域相对于先前研究的种群显示出数值和结构上的差异。我们描述了该物种在雄性中的四个新二倍体数，从2n = 12到2n = 15，共有七种不同的细胞类型，并且我们分析了在减数分裂（II，III，V，VI，VII）期间观察到的不同多价关联所涉及的染色体重排和IX）。核糖体DNA始终存在于两个染色体中每个染色体的一个末端区域。在不同细胞类型的每个染色体的末端区域，都发现了不同大小的组成型异染色质块，以及在某些染色体中的亚末端和间质块。基于rDNA和组成型异染色质定位，我们分析了这些种群中的染色体进化。我们建议所有细胞型可能起源于减数分裂I的2n = 18和9个二价假想祖先核型，但遵循两条途径，具有不同的主要融合序列和祖先核型的一些易位。此外，我们审查了该物种的所有细胞遗传学研究种群及其分布，以讨论该多态物种的染色体进化。