Cytogenetic variability in four species of Gnamptogenys Roger, 1863 (Formicidae: Ectatomminae) showing chromosomal polymorphisms, species complex, and cryptic species

Abstract

Gnamptogenys includes 138 described species that are widely distributed, with high diversity, in the Neotropics. Some Neotropical species have taxonomic issues, as is the case with Gnamptogenys striatula, for which morphological variations have been observed between different populations. For the ant species with taxonomic issues, classical and molecular cytogenetic studies have assisted in the resolution of these issues. Cytogenetic studies of Gnamptogenys are scarce and have only been reported for 14 taxa. These reports have rarely presented chromosomal morphology. Considering the importance of the taxonomic revision of some species, such as G. striatula, the present study cytogenetically characterized four species of Gnamptogenys: G. striatula, G. moelleri, G. regularis, and G. triangularis, discussing their phylogenetic and biogeographic characteristics. The number of chromosomes ranged from 2n = 26 to 2n = 44, with distinct karyotypes at both species and population levels. All four species presented a pair of 18S rDNA gene markers that coincided with GC-rich regions. In the case of G. striatula from the Atlantic rainforest, a chromosomal polymorphism was observed, with chromosomal translocations being the likely origin of this polymorphism. Two populations of G. striatula showed karyotype differences, thus corroborating previous morphological data indicating the existence of a species complex in this taxon. In addition, G. regularis showed a polymorphism involving a chromosome pair bearing ribosomal genes, possibly caused by unequal crossing-over. Although G. moelleri has a well-defined taxonomy, a population from the eastern Amazon rainforest presented a divergent karyotype from the Atlantic rainforest populations, suggesting the existence of a cryptic species in this taxon.