Cytogenetics of Four Turtle Ants from the Amazon: First Steps Towards Understanding Karyotype Evolution in Cephalotes

Ants of the genus Cephalotes have unique morphological traits, with morphotypes specifically adapted to arboreal habitats, earning them the common name "turtle ants". In the Americas, 118 Cephalotes spp. have been identified, 64 in Brazil. Phylogenetic studies suggest 15 distinct groups of Cephalotes spp. In this context, cytogenetics emerges as a valuable tool for comprehending the diversification of these clades. This study used cytogenetics to characterize four Cephalotes spp. from the northernmost Brazilian state of Amapá. The number, morphology, and locations of specific DNA sequences varied. Most chromosomes were metacentric; C. atratus had a low chromosome number (2n = 22), compared to C. minutus, C. pavonii, and C. simillimus (2n = 44, 2n = 42, and n = 22, respectively). Ribosomal genes were restricted to a single chromosome pair which were present within pericentromeric regions in C. atratus and C. simillimus, interstitial region in C. pavonii and terminal region in C. minutus. The microsatellite (GA)_n was clustered only in C. atratus; whereas in species with high chromosome numbers, this microsatellite was absent on one arm of several chromosome pairs. The telomeric (TTAGG)n motif was restricted to the chromosome ends in C. atratus as expected. Our findings suggest that centric fission, along with occasional chromosomal inversion events are principal mechanisms driving karyotype evolution in Cephalotes spp. Combining the cytogenetic data on Procryptocerus spp., we suggest that the putative ancestral karyotype of Cephalotes has 2n = 22 chromosomes. Cytogenetic analyses of a broader diversity of Cephalotes spp. are essential to elucidate whether fission events represent lineage-specific innovations or shared ancestral processes. They may provide deeper insights into the evolutionary dynamics underlying chromosomal architecture and its role in the diversification of these ecologically specialized turtle ants.