Atlantic surgeonfishes bear only minor microstructural changes in highly derived karyotypes

Acanthurus is a representative and widespread genus of marine fish that plays a key role in ecological dynamics of coral reefs. Three species are common along coastal reefs of Western Atlantic: A. coeruleus, A. bahianus, and A. chirurgus. The cytogenetic patterns of these species indicated sequential steps of chromosomal rearrangements dating back 19–5 millions of years ago (M.a.) that accounted for their interspecific differences. A. coeruleus (2n = 48; 2sm + 4st + 42a), A. bahianus (2n = 36; 12m + 2sm + 4st + 18a), and A. chirurgus (2n = 34; 12m + 2sm + 4st + 16a) share an older set of three chromosomal pairs that were originated through pericentric inversions. A set of six large metacentric pairs formed by Robertsonian (Rb) translocations found in A. bahianus and A. chirurgus and a putative in tandem fusion found in A. chirurgus are more recent events. In the present study, new cytogenetic data are being reported for these three Acanthurus species based on mapping of repetitive sequences such as ribosomal 18S and 5S rDNA and telomeric repeats to improve their karyotype evolutionary analyses. The lack of interstitial telomeric sequences (ITS) in spite of several centric fusions in A. bahianus and A. chirurgus might be related to the long period of time after their occurrence (estimated in 5 M.a.). Furthermore, the homeologies among the chromosome pairs bearing ribosomal genes, in addition to other structural features, highlight large conserved chromosomal regions in the three species. Our findings indicate that macrostructural changes occurred during the cladogenesis of these species were not followed by conspicuous microstructural rearrangements in the karyotypes.