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The trap-jaw ant Acanthognathus Mayr (Myrmicinae: Dacetina) has been subject of various studies since 1969, but there has been no progress in its cytogenetics. This study describes provides the first karyotype description of a representative of the genus, A. rudis, including chromosomal number, morphology, and the distribution of repetitive sequences. A colony collected in Southeastern Brazil exhibited a diploid number of 2n = 14 (12 metacentrics + 2 submetacentrics), the lowest number among the Daceton genus-group and the first Neotropical representative of this group to be karyologically studied. The rDNA clusters were located in the pericentromeric region of a single chromosome pair, (GA)n blocks were present only in the terminal regions of both chromosome arms in the euchromatic regions, and (TTAGG)n hybridized with the telomeres of all chromosomes, without interstitial telomeric sites. The repetitive sequence patterns align with those observed in other Neotropical Formicidae. Additionally, we documented new behavioral aspects of mandible use in A. rudis workers and provided the first images of its immature stages. These findings emphasize the need for further research on Acanthognathus and the other Daceton genus-group.

The Brazilian Atlantic rainforest is an endangered biome and biodiversity hotspot. Ant cytogenetic studies from this biome showed remarkable chromosomal diversity among species, and provided useful insights on phylogeny, chromosomal evolution, and taxonomy. In this study, we karyotyped five ant taxa from the Atlantic rainforest. The karyotypes observed were Pheidole germaini 2n=22, Pheidole sp. flavens group 2n=20, Brachymyrmex admotus 2n=18, Camponotus atriceps 2n=40, and Odontomachus haematodus 2n=44. The data obtained for Pheidole spp. represent the first chromosomal record for the genus in Brazil and provide insights on the chromosomal evolution of P. germaini. Karyotypic information from B. admotus brings the genus back to the cytogenetic scenario after decades of neglect. No karyotype variations were observed among the C. atriceps and O. haematodus from different already studied populations, corroborating their status as good species. This study increased the cytogenetic knowledge of ants from the Brazilian Atlantic rainforest.

Over the past several decades, ant cytogenetic studies have focused on chromosome number and morphology; however, recently, additional information concerning heterochromatin composition and 45S rDNA location has become accessible. The fungus-growing ants are a peculiar ant group that cultivates fungus for food, and Trachymyrmex is suspected to be the sister group of leafcutter ants. Cytogenetic data are so far available for sixn Trachymyrmex species. The present study aimed to increase the knowledge about Trachymyrmex cytogenetics by the chromosomal characterization of Trachymyrmex holmgreni including the karyotyping, fluorochromes staining, 18S rDNA, and microsatellite (GA)15 fluorescence in situ hybridization (FISH). Karyotyped samples from four ant colonies showed 2n = 20 metacentric chromosomes. Centromeric heterochromatin rich in GC base pairs was detected in all chromosomes. FISH revealed the presence of rDNA clusters on the fourth chromosome pair, and an intense spreading of the microsatellite (GA)15 including exclusively euchromatic areas of the chromosomes. The GC-rich heterochromatin observed in different ant species may have a common origin and, thus, phylogenetic implication that needs to be further investigated. To the best of our knowledge, this study is the first report of the use of chromosomal physical location of repetitive DNA sequences by means of microsatellite probes in Formicidae.

Cephalotrigona femorata (Smith, 1854) was submitted to cytogenetic techniques to study and describe its karyotype. Conventional staining allowed the counting (2n=34) and observation of chromosome morphology. The amount and distribution of heterochromatin in this species was different from Cephalotrigona capitata (Smith, 1854), another species of the genus already analyzed. Our results indicate that heterochromatin a potential marker for the genus, at least for the species found in Brazil. This region was marked by DAPI, revealing a high content of A:T. The CMA3 marked two pairs, and it seems to be polymorphic in one pair.