Common Descent of B Chromosomes in Two Species of the Fish Genus <b><i>Prochilodus</i></b> (Characiformes, Prochilodontidae)

Abstract

To ascertain the origin of B chromosomes in 2 fish species of the genus Prochilodus, i.e. P. lineatus and P. nigricans, we microdissected them and generated B-specific DNA probes. These probes were used to perform chromosome painting in both species and in 3 further ones belonging to the same genus (P. argenteus, P. brevis and P. costatus). Both probes hybridized with the B chromosomes in P. lineatus and P. nigricans, but with none of the chromosomes in the 5 species. This indicates that the B chromosomes have low similarity with DNAs located in the A chromosomes and suggests the possibility that the B chromosomes in the 2 species have a common origin. The most parsimonious explanation would imply intergeneric hybridization in an ancestor of P. lineatus and P. nigricans yielding the B chromosome as a byproduct, which remained in these 2 species after their phylogenetic origin, but was perhaps lost in other Prochilodus species. This hypothesis predicts that B chromosomes are old genomic elements in this genus, and this could be tested once a species from a relative genus would be found showing homology of its A chromosomes with the B-probes employed here, through a comparison of B chromosome DNA sequences with those in the A chromosomes of this other species.

B chromosome dynamics in Prochilodus costatus (Teleostei, Characiformes) and comparisons with supernumerary chromosome system in other Prochilodus species

“…2). Notably, this hybridization pattern evidenced that all B chromosomes analyzed in this study shared anonymous sequences, as already reported for P. lineatus and P. nigricans (Voltolin et al 2013b). The identical hybridization pattern generated throughout chromosome painting between different species or populations allow us to suggest that these B chromosomes show a high degree of homology.…”

“…3; arrowheads). Notably, SATH1 sequences were also extensively spread over several A chromosomes in all species, whereas the BPC and all previously microdissected B-probes of Prochilodus (Voltolin et al 2013b) revealed signals only on the B chromosomes. Such deviation might be caused by a possible bias of amplification in the GenomePlex reaction.…”

“…Prochilodus costatus Valenciennes, 1850 is an endemic species of the São Francisco River basin and previous cytogenetic analyses did not reveal the presence of B chromosomes in this species (Pauls and Bertollo 1990, Galetti 1991, Voltolin et al 2013a, 2013b). In this study, we described the occurrence of B chromosomes in P. costatus for the first time and performed a comparative analysis with other B chromosome systems found in P. lineatus and P. argenteus using chromosome painting and mapping of SATH1 satDNA.…”

“…Although chromosome numbers and karyotype structure are highly stable in Prochilodus species, the frequency of different B chromosomes in distinct species/populations is remarkable (Cavallaro et al 2000, Artoni et al 2006, Penitente et al 2015). For instance, two populations of P. costatus were analyzed until now and none of them showed B chromosomes in their cells (Pauls and Bertollo 1990, Voltolin et al 2013a, 2013b). In fact, supernumerary chromosomes in fish are usually highly dynamic elements, and the existence of B-lacking and B-carrying populations is quite common and largely known (Oliveira et al 2009).…”

The B Chromosomes of Prochilodus lineatus (Teleostei, Characiformes) Are Highly Enriched in Satellite DNAs

“…In addition, all populations of P. lineatus analyzed to date exhibit a B chromosome system composed of at least three micro-B variants [ 14 , 19 , 20 , 21 ]. Likewise, congeneric species also show similar micro-B chromosomes and it is hypothesized that these elements originated in the last common ancestor of several Prochilodus species [ 22 , 23 ]. In a pioneering study, Jesus et al [ 24 ] isolated two pericentromeric satDNAs from the genome of P. lineatus (SATH1 and SATH2) out of which one (SATH1) was also clustered on the B chromosomes, suggesting an intraspecific origin for these elements [ 14 , 24 ].…”