Abstract
Ants are present in different environments and regions of the planet, showing little-known biodiversity in the Neotropics, especially among fungus-growing ants (the subtribe Attina). Recent studies seek to combine morphological analysis with other methods, such as cytogenetics, to better define and differentiate species. In this sense, cytogenetic analyses have been important for the study of ants, characterizing chromosome number and morphology, and mapping rDNA genes and microsatellites, which generate important information about the evolution and taxonomy in Attina species. In the Amazon region, there are still few studies that include cytogenetics in their research. In this study, we cytogenetically characterized five fungus-growing ants, belonging to the genera Cyphomyrmex Mayr, 1862 and Apterostigma Mayr, 1865, from the northernmost region of Amapá state within the Guiana Shield region of Brazil. The nests were captured by active search, and the larvae had their brain ganglia extracted to provide metaphase chromosomes. The karyotypes were determined using Giemsa or DAPI staining, and 18S ribosomal DNA (rDNA) and (GA)(n) microsatellite repetitive sequences were physically mapped with FISH technique with specific probes. Cyphomyrmex transversus Emery, 1894 had 2n = 24 chromosomes (18m+6sm) and Cyphomyrmex laevigatus Weber, 1938 n = 7, all metacentrics. In both species, the rDNA clusters were restricted to a single chromosome pair. In C. transversus the rDNA clusters were mapped to the long arm of the larger submetacentric chromosome pair, while in C. laevigatus they were on the short arm of the fifth chromosome (haploid individuals). These data are aligned to Cyphomyrmex species previously studied from this region. Although the FISH protocol was successfully applied to Cyphomyrmex species, it was unable to localize rDNA sites in the chromosomes of all three Apterostigma species, suggesting that methodological adjustments are required for an effective application to this genus. In Apterostigma, the largest chromosome number of the genus was identified in Apterostigma tropicoxa Lattke, 1997, with 2n = 54 chromosomes, while A. jubatum Wheeler, 1925 and A. andense Lattke, 1997 had 2n = 22 and n = 11 respectively but were strikingly diverse in their karyotype configurations. In C. laevigatus and C. transversus the microsatellite (GA)(n) clusters were scattered on all chromosomes. While A. jubatum also had a scattered distribution pattern of this microsatellite on all chromosomes, the other Apterostigma species showed more complex patterns. In A. andense these microsatellite sequences were more concentrated at the ends of some chromosomes, while in Apterostigma tropicoxa they were almost absent in the short arms of several submetacentric and subtelocentric chromosomes. The cytogenetic data for Amazonian species in this study highlight the chromosomal diversity among fungus-growing ants, particularly within the genus Apterostigma, providing useful insights into the karyotype evolution of these ants and paving the way for further cytogenetic research in the Amazon region.