Santos, I.S., Mariano, C.S.F., Delabie, J.H.C., Costa, M.A., Carvalho, A.F. & Silva, J.G.

"Much more than a neck": karyotype differentiation between Dolichoderus attelaboides (Fabricius, 1775) and Dolichoderus decollatus F. Smith, 1858 (Hymenoptera: Formicidae) and karyotypic diversity of five other Neotropical species of Dolichoderus Lund, 1831

Dolichoderus Lund, 1831 is the most species-rich and morphologically diverse genus in the Dolichoderinae subfamily and comprises more than 150 described species. The ants in this genus are mainly arboreal and are mostly found in tropical humid forests. In Brazil, there are 35 Dolichoderus species grouped in nine species complexes. Some of these species, such as those in the D. attelaboides and D. decollatus complexes, are large in overall size and share several common morphological characters, which suggests a close phylogenetic relationship among them. In this study, classical and molecular cytogenetic techniques were used to investigate the karyotype differentiation between Dolichoderus attelaboides (Fabricius, 1775) (D. attelaboides complex) and Dolichoderus decollatus F. Smith, 1858 (D. decollatus complex). Also, species in the following complexes were analyzed cytogenetically for the first time, namely Dolichoderus lutosus (F. Smith, 1858), Dolichoderus diversus Emery, 1894, and Dolichoderus voraginosus Mackay, 1993 (D. diversus complex), Dolichoderus bidens (Linnaeus, 1758) (D. bidens complex), and Dolichoderus imitator Emery, 1894 (D. imitator complex). Our results revealed a high karyotype divergence between D. attelaboides and D. decollatus, indicating that chromosome rearrangements most likely had an important role in the diversification of these complexes. The chromosome numbers analyzed in this study ranged from 2n = 10 to 2n = 58 and placed Dolichoderinae as the third most karyotypically diverse group known within Formicidae. The differences in the location of Dna clusters between the two species in the D. diversus complex may have originated from pericentric inversions during karyotype diversification within this complex. Molecular phylogenetic analyses using fragments of the cytochrome oxidase I (COI) and long-wavelength rhodopsin (Lw Rh) genes indicated that chromosomal rearrangements have played an important role in karyotype evolution and diversification in Dolichoderus, unlike other ant genera that exhibit highly conserved karyotypes. We conclude that the smaller and more numerous chromosomes arose as a result of successive events of fission.