Chromosome Mapping of Ribosomal DNA Clusters in Four Leaf-cutting Ant Species of the Genus Acromyrmex, with Description of a Triploid Individual in A. laticeps

Abstract

The increase of cytogenetic data in the leaf-cutting genus Acromyrmex has shown interesting contributions to the evolutionary and taxonomic approaches, including the creation of a new genus and the description of chromosomal patterns allowing comparative studies within Acromyrmex as well as between this genus and other similar taxa. The conserved chromosome number in Acromyrmex is a notable feature, with some distinguishable chromosomes among the species. In this study, we describe the diploid karyotype of Acromyrmex laticeps in addition to an individual with all the metaphases triploids, suggesting a triploid individual. To the best of our knowledge, this is the first report of polyploidy in a fungus-growing ant. Furthermore, we mapped 18S ribosomal DNA on the chromosomes of A. laticeps and three other Acromyrmex species. Among them, three species showed the ribosomal DNA cluster pattern observed in other previously studied members of this genus, with a terminal location in the largest subtelocentric pair. Meanwhile, Acromyrmex balzani had these ribosomal DNA clusters in its entire short arm. The role of triploidy in ant evolution has also been discussed. The increase in chromosomal data of leaf-cutting ants may provide significant insights into the evolution of this peculiar ant group.