Repetitive DNA Sequences and Evolution of ZZ/ZW Sex Chromosomes in Characidium (Teleostei: Characiformes)

Abstract

Characidium constitutes an interesting model for cytogenetic studies, since a large degree of karyotype variation has been detected in this group, like the presence/absence of sex and supernumerary chromosomes and variable distribution of repetitive sequences in different species/populations. In this study, we performed a comparative cytogenetic analysis in 13 Characidium species collected at different South American river basins in order to investigate the karyotype diversification in this group. Chromosome analyses involved the karyotype characterization, cytogenetic mapping of repetitive DNA sequences and cross-species chromosome painting using a W-specific probe obtained in a previous study from Characidium gomesi. Our results evidenced a conserved diploid chromosome number of 2n = 50, and almost all the species exhibited homeologous ZZ/ZW sex chromosomes in different stages of differentiation, except C. cf. zebra, C. tenue, C. xavante and C. stigmosum. Notably, some ZZ/ZW sex chromosomes showed 5S and/or 18S rDNA clusters, while no U2 snDNA sites could be detected in the sex chromosomes, being restricted to a single chromosome pair in almost all the analyzed species. In addition, the species Characidium sp. aff. C. vidali showed B chromosomes with an inter-individual variation of 1 to 4 supernumerary chromosomes per cell. Notably, these B chromosomes share sequences with the W-specific probe, providing insights about their origin. Results presented here further confirm the extensive karyotype diversity within Characidium in contrast with a conserved diploid chromosome number. Such chromosome differences seem to constitute a significant reproductive barrier, since several sympatric Characidium species had been described during the last few years and no interespecific hybrids were found.

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

“…In particular, rDNA sequences have been supposed to play some role in the evolutionary process of the sex chro-201 mosomes in different vertebrate groups [Kawai et al, 2007;Abramyan et al, 2009], including several fish species [Reed and Philips, 1995;Scacchetti et al, 2015;Ferreira et al, 2016;Yano et al, 2016]. It is known that the accumulation of repetitive DNAs is one of the main evolutionary forces that drive karyotype and sex chromosome differentiation [Wichman et al, 1991;Hamilton et al, 1992;Pucci et al, 2014].…”

Chromosomal Spreading of Microsatellites and (TTAGGG)_n Sequences in the <b><i>Characidium zebra </i></b>and<b><i> C. gomesi </i></b>Genomes (Characiformes: Crenuchidae)

“…This genus belongs to the Crenuchidae family which is composed of 71 valid species [Eschmeyer et al, 2015]. All Characidium species hitherto cytogenetically studied have a diploid chromosome number of 2n = 50 [for a review, see Pucci et al, 2014;Scacchetti et al, 2015c].…”

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)

“…The association of ribosomal sequences with sex chromosomes is a characteristic already known for several vertebrate groups [Born and Bertollo, 2000;Kawai et al, 2007;Abramyan et al, 2009;Kawagoshi et al, 2009Kawagoshi et al, , 2014O'Meally et al, 2010;Cioffi et al, 2011;Scacchetti et al, 2015;Ferreira et al, 2016]. For example, in the characid genus Triportheus (Triportheidae), the W chromosome harbors an 18S rDNA cistron in the terminal region of the q arms, which is missing in the Z chromosome in the majority of the species [Yano et al, 2016a].…”