Comparative physical mapping of 18S rDNA in the karyotypes of six leafcutter ant species of the genera Atta and Acromyrmex (Formicidae: Myrmicinae)

Abstract

Leafcutter ants of the Atta and Acromyrmex genera are important plagues in different cultures. Cytogenetic data on chromosome number, morphology, and chromosomal banding pattern are only available for 17 species of leafcutter ants. Molecular cytogenetic data for the detection of ribosomal genes by the FISH technique are scarce, and only 15 Neotropical ant species have been studied. This study aimed to physically map the 18S ribosomal RNA genes (rDNA) of six leafcutter ants belonging to the genera Atta and Acromyrmex using FISH. The results were compared with data on the fluorochrome CMA currently available for these species. All analyzed species presented the 18S rDNA on one pair of chromosomes. In Acromyrmex subterraneus molestans and Ac. aspersus, FISH signals were observed in the terminal region of the short arm of the largest subtelocentric pair, while in Atta bisphaerica, A. laevigata, and A. sexdens, FISH signals were observed in the interstitial region of the long arm of the fourth metacentric pair. In Acromyrmex striatus, 18S rDNA was located in the interstitial region of the second metacentric pair. The karyotypic formula for Ac. aspersus was 2n = 38 (8m + 10sm + 16st + 4a), representing the first report in this species. The observed 18S rDNA regions in A. laevigata, A. sexdens, A. bisphaerica, Ac. aspersus, and Ac. subterraneus molestans corresponded to the CMA bands, while in Ac. striatus, several GC-rich bands and one pair of 18S rDNA bands were observed. No differential bands were visible using the DAPI fluorochrome. Karyotype uniformity with previously studied Atta spp. was also observed at the level of molecular cytogenetics using 18S rDNA FISH. A difference in the size of the chromosomal pair carrying the 18S rDNA gene was observed in Ac. striatus (2n = 22) and Atta spp. (2n = 22) highlighting the dissimilarity between these species. The results from the present study contribute to the description of 18S rDNA clusters in Neotropical ants.

Cytogenetic studies in Trachymyrmex holmgreni Wheeler, 1925 (Formicidae: Myrmicinae) by conventional and molecular methods

“…This was also observed in other fungusgrowing ants such as M. goeldii (Barros et al, 2010(Barros et al, , 2012, A. niger (Barros et al, 2016) and Ac. striatus (Cristiano et al, 2013, Teixeira et al 2017.…”

“…striatus (Cristiano et al, 2013). However, most Acromyrmex (2n = 38) and all Atta species already studied have a single pair of 18S rDNA rich in GC (Barros et al, 2014b(Barros et al, , 2015(Barros et al, , 2016Teixeira et al, 2017). It is suggested that Ac.…”

“…Other cytogenetic techniques including fluorescent in situ hybridization (FISH) using rDNA probes have been used to detect differences among fungus-growing ants (Barros et al, 2016;Teixeira et al, 2017). The detection of heterochromatic GC-rich regions using the fluorochrome CMA 3 pointed to single bands for most species of the Neotropical region, including the leafcutter ants of the genus Atta (Barros et al, 2014b(Barros et al, , 2015 and Acromyrmex (Barros et al, 2016).…”

“…In ants from the Neotropical region, the reports of 18S or 45S physical location are available for 25 species (Mariano et al, 2008;Aguiar et al, 2011;Santos et al, 2010Santos et al, , 2016Barros et al, 2012Barros et al, , 2015Barros et al, , 2016Teixeira et al, 2017;Aguiar et al, 2017). The majority of these species present the GC-rich regions coinciding with the nucleolus organizer regions (NORs).…”

“…The exceptions are M. goeldii (Barros et al, 2010(Barros et al, , 2012, Acromyrmex niger (Smith, 1858) ( Barros et al, 2016), Dolichoderus lutosus (Smith, 1858), Dolichoderus voraginosus MacKay, 1993, Dolichoderus bidens( Linnaeus, 1758) (Santos et al, 2016), and Ac. striatus (Cristiano et al, 2013;Teixeira et al, 2017), which presented multiple GCrich heterochromatic bands and a single pair of NORs.…”