Cytogenetic studies on fungus-farming ants have shown remarkable karyotype diversity, suggesting different chromosomal rearrangements involved in karyotype evolution in some genera. A notable cytogenetic characteristic in this ant group is the presence of GC-rich heterochromatin in the karyotypes of some ancient and derivative species. It was hypothesized that this GC-rich heterochromatin may have a common origin in fungus-farming ants, and the increase in species studied is important for understanding this question. In addition, many genera within the subtribe Attina have few or no cytogenetically studied species; therefore, the processes that shaped their chromosomal evolution remain obscure. Thus, in this study, we karyotyped, through classical and molecular cytogenetic techniques, the fungus-farming ants Cyphomyrmex transversus Emery, 1894, Sericomyrmex maravalhas Ješovnik et Schultz, 2017, and Mycetomoellerius relictus (Borgmeier, 1934), to provide insights into the chromosomal evolution in these genera and to investigate the presence the GC-rich heterochromatin in these species. Cyphomyrmex transversus (2n = 18, 10m + 2sm + 6a) and S. maravalhas (2n = 48, 28m + 20sm) showed karyotypes distinct from other species from their genera. Mycetomoellerius relictus (2n = 20, 20m) presented the same karyotype as the colonies previously studied. Notably, C. transversus presented the lowest chromosomal number for the genus and a distinct karyotype from the other two previously observed for this species, showing the existence of a possible species complex and the need for its taxonomic revision. Chromosomal banding data revealed GC-rich heterochromatin in all three species, which increased the number of genera with this characteristic, supporting the hypothesis of a common origin of GC-rich heterochromatin in Attina. Although a single chromosomal pair carries rDNA genes in all studied species, the positions of these rDNA clusters varied. The rDNA genes were located in the intrachromosomal region in C. transversus and M. relictus, and in the terminal region of S. maravalhas. The combination of our molecular cytogenetic data and observations from previous studies corroborates that a single rDNA site located in the intrachromosomal region is a plesiomorphic condition in Attina. In addition, cytogenetic data obtained suggest centric fission events in Sericomyrmex Mayr, 1865, and the occurrence of inversions as the origin of the location of the ribosomal genes in M. relictus and S. maravalhas. This study provides new insights into the chromosomal evolution of fungus-farming ants.

中文翻译：

---

三种真菌养殖蚂蚁（Myrmicinae、Attini、Attina）中富含 GC 的异染色质和核糖体基因的分布：对染色体进化的见解

对种植真菌的蚂蚁的细胞遗传学研究显示出显着的核型多样性，表明某些属的核型进化涉及不同的染色体重排。该蚂蚁群的一个显着细胞遗传学特征是在一些古老和衍生物种的核型中存在富含 GC 的异染色质。假设这种富含 GC 的异染色质可能在真菌养殖蚂蚁中具有共同的起源，并且研究物种的增加对于理解这个问题很重要。此外，亚部落 Attina 内的许多属很少或没有细胞遗传学研究的物种。因此，塑造它们染色体进化的过程仍然不清楚。因此，在这项研究中，我们通过经典和分子细胞遗传学技术对真菌养殖蚂蚁 Cyphomyrmex transversus Emery，1894 年进行了核型分析，Sericomyrmex maravalhas Ješovnik et Schultz, 2017 和 Mycetomoellerius relictus (Borgmeier, 1934)，提供对这些属中染色体进化的见解，并研究这些物种中富含 GC 的异染色质的存在。Cyphomyrmex transversus (2n = 18, 10m + 2sm + 6a) 和 S. maravalhas (2n = 48, 28m + 20sm) 显示出与其他物种不同的核型。Mycetomoellerius relictus (2n = 20, 20m) 呈现与先前研究的菌落相同的核型。值得注意的是，C. transversus 显示出该属的最低染色体数，并且与之前对该物种观察到的其他两个不同的核型显示出可能的物种复合体的存在及其分类学修订的必要性。染色体显带数据揭示了所有三个物种中富含 GC 的异染色质，这增加了具有这种特征的属的数量，支持了 Attina 中富含 GC 的异染色质的共同起源的假设。尽管在所有研究物种中，单个染色体对都携带 rDNA 基因，但这些 rDNA 簇的位置各不相同。rDNA 基因位于 C. transversus 和 M. relictus 的染色体内区域，以及 S. maravalhas 的末端区域。我们的分子细胞遗传学数据和先前研究的观察结果相结合，证实了位于染色体内区域的单个 rDNA 位点是 Attina 的同形性条件。此外，获得的细胞遗传学数据表明，1865 年 Sericomyrmex Mayr 发生了中心裂变事件，并且发生倒位是 M. relictus 和 S. maravalhas 中核糖体基因位置的起源。