Trichechus manatus and Trichechus inunguis are the two Sirenia species that occur in the Americas. Despite their increasing extinction risk, many aspects of their biology remain understudied, including the repetitive DNA fraction of their genomes. Here we used the sequenced genome of T. manatus and TAREAN to identify satellite DNAs (satDNAs) in this species. We report the first description of TMAsat, a satDNA comprising ~0.87% of the genome, with ~684bp monomers and centromeric localization. In T. inunguis, TMAsat showed similar monomer length, chromosome localization and conserved CENP-B box-like motifs as in T. manatus. We also detected this satDNA in the Dugong dugon and in the now extinct Hydrodamalis gigas genomes. The neighbor-joining tree shows that TMAsat sequences from T. manatus, T. inunguis, D. dugon, and H. gigas lack species-specific clusters, which disagrees with the predictions of concerted evolution. We detected a divergent TMAsat-like homologous sequence in elephants and hyraxes, but not in other mammals, suggesting this sequence was already present in the common ancestor of Paenungulata, and later became a satDNA in the Sirenians. This is the first description of a centromeric satDNA in manatees and will facilitate the inclusion of Sirenia in future studies of centromeres and satDNA biology.

We studied the chromosomes of Callicebus nigrifrons with conventional and molecular cytogenetic methods. Our chromosome painting analysis in C. nigrifrons together with previous reports allowed us to hypothesize an ancestral Callicebinae karyotype with 2n = 48. The associations of human chromosomes (HSA) 2/22, 7/15, 10/11, and the inverted HSA2/16 would link Callicebus, Cheracebus, and Plecturocebus and would thus be present in the ancestral Callicebinae karyotype. Four fusions (HSA1b/1c, 3c/8b, 13/20, and 14/15/3/21) and 1 fission (HSA2/22) are synapomorphies of Callicebus. The associations HSA3/15 and HSA3/9 are chromosome features linking Callicebus and Cheracebus, whereas the association HSA13/17 would represent a link between Callicebus and the moloch group (Plecturocebus). Only 6 of the 33 recognized titi monkey species have now been painted with human chromosome-specific probes. Further analyses are needed to clarify the phylogenomic relationships in this species-rich group.

Xenarthra, one of the four mammalian superorders, is exclusively found in Central and South America and is possibly positioned at the base of the Eutherian phylogenetic tree. Cytogenetic studies of this group are very few and mainly restricted to the description of the karyotypes after conventional staining, with just a few reported banding patterns. We analyzed the chromosomes of a male Choloepus didactylus (Linnaeus’s two-toed sloth) from Rondônia after GTG- and CBG-banding and silver staining of the nucleolus organizer regions(Ag-NOR). Our specimen presented a karyotype with 2n=51, NF=60, which has not been reported yet for this species. The GTG-banding allowed us to establish the correspondence among all chromosome pairs and was also important to verify a Y/18 autosome translocation, which seems to be characteristic of Choloepus. CBG-banding revealed pericentromeric heterochromatin in all chromosomes, except for the X. Four medium acrocentric autosomes presented Ag-NORs in their short arms. Until now the diploid numbers described for the few individuals of C. didactylus analyzed range from 2n=52-65. The finding of a new karyotype with 2n=51 in our specimen reinforces the need of further studies of this species, which is also taxonomically poorly understood and probably contains several still unidentified taxa. In addition, chromosome studies in Xenarthra are very likely to yield important insights into mammalian genome evolution.