Is the Karyotype of Neotropical Boid Snakes Really Conserved? Cytotaxonomy, Chromosomal Rearrangements and Karyotype Organization in the Boidae Family

Abstract

Boids are primitive snakes from a basal lineage that is widely distributed in Neotropical region. Many of these species are both morphologically and biogeographically divergent, and the relationship among some species remains uncertain even with evolutionary and phylogenetic studies being proposed for the group. For a better understanding of the evolutionary relationship between these snakes, we cytogenetically analysed 7 species and 3 subspecies of Neotropical snakes from the Boidae family using different chromosomal markers. The karyotypes of Boa constrictor occidentalis, Corallus hortulanus, Eunectes notaeus, Epicrates cenchria and Epicrates assisi are presented here for the first time with the redescriptions of the karyotypes of Boa constrictor constrictor, B. c. amarali, Eunectes murinus and Epicrates crassus. The three subspecies of Boa, two species of Eunectes and three species of Epicrates exhibit 2n = 36 chromosomes. In contrast, C. hortulanus presented a totally different karyotype composition for the Boidae family, showing 2n = 40 chromosomes with a greater number of macrochromosomes. Furthermore, chromosomal mapping of telomeric sequences revealed the presence of interstitial telomeric sites (ITSs) on many chromosomes in addition to the terminal markings on all chromosomes of all taxa analysed, with the exception of E. notaeus. Thus, we demonstrate that the karyotypes of these snakes are not as highly conserved as previously thought. Moreover, we provide an overview of the current cytotaxonomy of the group.

Genomic Organization of Repetitive DNAs and Differentiation of an XX/XY Sex Chromosome System in the Amazonian Puffer Fish, <b><i>Colomesus asellus </i></b>(Tetraodontiformes)

“…Likewise, a similar pattern has been identified in several species with subtly differentiated XY sex chromosomes, suggesting a differential accumulation of 18S rDNA sequences [Cioffi et al, 2010;Kawagoshi et al, 2014]. However, the degeneration of the sex-specific chromosome is not a necessarily required event, as attested by cases where the sex pair remains morphologically identical [Mank and Ellegren, 2007;Matsubara et al, 2015;Viana et al, 2016], as has also already been observed in several Tetraodontidae species [Kamiya et al, 2012]. In addition, sex chromosomes can evolve independently among vertebrates, even among closely related species [Mank et al, 2006;Matsubara et al, 2006;Henning et al, 2008;Ezaz et al, 2009;Cioffi et al, 2011;Matsubara et al, 2014].…”

Evolutionary Relationships among <b><i>Boulengerella</i></b> Species (Ctenoluciidae, Characiformes): Genomic Organization of Repetitive DNAs and Highly Conserved Karyotypes

“…In Boulengerella , they show the expected distribution pattern in the telomeres of all chromosomes. However, an ITS was also observed in the centromeric region of pair 3 in B. lateristriga, B. cuvieri , and B. maculata , which may reflect possible rearrangements that have occurred during their evolutionary history, such as chromosomal fusions or inversions as documented for many other vertebrate species [Meyne et al, 1990;Wiley et al, 1992;Rosa et al, 2012;Viana et al, 2016]. Additionally, ITSs may also be related to a telomerase process to recover chromosome breaks, in which telomeric sequences are added to non-terminal regions of the chromosomes [Flint et al, 1994;Azzalin et al, 2001;Nergadze et al, 2007].…”

Cytogenetics of two Farlowella species (Loricariidae: Loricariinae): implications on the taxonomic status of the species

“…14. An association between intra-chromosomal telomeric DNA and constitutive heterochromatin has been recorded in many vertebrates, and this association is considered a component of the satellite DNA (Meyne et al, 1990;Multani et al, 2001;Rovatsos et al, 2015;Viana et al, 2016). These signals may also represent remnants of ancient chromosomal rearrangements (Metcalfe et al, 2004), indicating potential hotspots of rearrangement (Scouarnec, Gribble, 2012).…”