Differential chromosomal organization between Saguinus midas and Saguinus bicolor with accumulation of differences the repetitive sequence DNA

Abstract

Saguinus is the largest and most complex genus of the subfamily Callitrichinae, with 23 species distributed from the south of Central America to the north of South America with Saguinus midas having the largest geographical distribution while Saguinus bicolor has a very restricted one, affected by the population expansion in the state of Amazonas. Considering the phylogenetic proximity of the two species along with evidence on the existence of hybrids between them, as well as cytogenetic studies on Saguinus describing a conserved karyotypic macrostructure, we carried out a physical mapping of DNA repeated sequences in the mitotic chromosome of both species, since these sequences are less susceptible to evolutionary pressure and possibly perform an important function in speciation. Both species presented 2n = 46 chromosomes; in S. midas, chromosome Y is the smallest. Multiple ribosomal sites occur in both species, but chromosome pairs three and four may be regarded as markers that differ the species when subjected to G banding and distribution of retroelement LINE 1, suggesting that it may be cytogenetic marker in which it can contribute to identification of first generation hybrids in contact zone. Saguinus bicolor also presented differences in the LINE 1 distribution pattern for sexual chromosome X in individuals from different urban fragments, probably due to geographical isolation. In this context, cytogenetic analyses reveal a differential genomic organization pattern between species S. midas and S. bicolor, in addition to indicating that individuals from different urban fragments have been accumulating differences because of the isolation between them.

Repetitive Sequence Distribution on Saguinus, Leontocebus and Leontopithecus Tamarins (Platyrrhine, Primates) by Mapping Telomeric (TTAGGG) Motifs and rDNA Loci

“…rDNA loci were mapped for the first time by FISH in Leontocebus fuscicollis , Leontopithecus rosalia and S. mystax in the current study. In contrast to a previous study, where classic silver stain permitted the detection of active NORs [ 11 , 29 ], we found both active and inactive rDNA loci in the species of the genus Saguinus . In particular, we detected rDNA probe signals on the p-arm of chromosome pairs 16 and 17 in Leontopithecus rosalia in agreement with a previous molecular evidence on Leontopithecus chrysomelas [ 14 ].…”

“…Indeed, on these chromosomes in the Saguinus species, we identified a positive C-band just below the centromere on the q arm; on the same homologs 16, 17 and 19–22 in Leontocebus fuscicollis, we found an enrichment of heterochromatin at the p arm and in Leontopithecus we found heterochromatin enrichment at the centromere and at the distal part of the p arms ( Figure 1 b and Figure 3 ). These results are in agreement with the previous comparison of the C-banding pattern performed on Leontopithecus rosalia and Saguinus midas , which showed differences in the variation, quantity and distribution of the non-centromeric constitutive heterochromatin [ 11 , 29 ]. Such a variable pattern of heterochromatin distribution often occurs among phylogenetically close species, even in other groups of mammals [ 22 ].…”

“…Our comparative analysis of inverted DAPI-banding reveals that the karyotypes of the genera Saguinus and Leontocebus mainly differ from Leontopithecus in the morphology of autosomal pairs 16, 17 and 19–22 ( Figure 2 ). For example, chromosome pairs 16–17 are either acrocentric, as in S. mystax in agreement with the previous reconstructions in S. midas and S. bicolor where the homologs are identified as pairs 20–22 [ 11 , 13 , 29 ], or are subtelocentric, as in Leontopithecus rosalia (current study) and in Leontopithecus chrysomelas [ 14 ].…”

“…The variation in number and topology of rDNA loci has been shown at the inter- and also at the intra-species level, most commonly explained as a consequence of chromosomal rearrangements, transposition events or ectopic recombination through association of rDNA loci with other chromosomal segments occurred during meiotic division [ 22 , 27 , 28 ]. The topology of rDNA loci has been identified in a few species of the genus Saguinus by classical and molecular methods [ 7 , 11 , 12 , 21 , 29 ], in Leontopithecus rosalia through silver staining [ 11 ] and in Leontopithecus chrysomelas by rDNA-FISH [ 14 ].…”

“…Furthermore, ITSs are often correlated with heterochromatinisation, especially at centromeric positions (het-ITSs) [ 19 , 20 ]. Among tamarins, the distribution of telomeric (TTAGGG) sequences has been studied in Saguinus oedipus [ 19 ], S. midas and S. bicolor [ 29 ].…”