Some units of the 5S rDNA of Solea senegalensis were amplified by PCR and sequenced. Three main PCR products (227, 441, and 2166 bp) were identified. The 227- and 441-bp fragments were characterized by highly divergent nontranscribed spacer sequences (referred to as NTS-I and NTS-II) that were 109 and 324 bp long, respectively, yet their coding sequences were nearly identical. The 2166-bp 5S rDNA unit was composed of two 5S rRNA genes separated by NTS-I and followed by a 1721-bp spacer containing the U2, U5, and U1 small nuclear RNA genes (snRNAs). They were inverted and arranged in the transcriptional direction opposite that of the 5S rRNA gene. This simultaneous linkage of 3 different snRNAs had never been observed before. The PCR products were used as probes in fluorescence in situ hybridization experiments to locate the corresponding loci on the chromosomes of S. senegalensis. A major 5S rDNA chromosomal site was located along most of the short arm of a submetacentric pair, while a minor site was detected near the centromeric region of an acrocentric pair.

No abstract

In the classical taxonomy, three Scomber species are distinguished: S. scombrus, S. australasicus, and S. japonicus. Yet, some fish taxonomists have recently recognized Scomber colias, inhabiting the Atlantic Ocean, as a separate species from S. japonicus, distributed in the Pacific Ocean. Such proposal was based on significant mitochondrial DNA divergence as well as great phenotypic variation among individuals from these two ocean basins. However, in the absence of nuclear DNA data this issue remains still controversial. In this study, a phylogenetic analysis of nuclear 5S rDNA sequences was performed. A total of 30 individuals of S. colias collected in the Atlantic and 34 specimens of S. japonicus from the Pacific were characterized. Moreover, nine individuals of Pacific S. australasicus and eight of Atlantic S. scombrus were included. Maximum likelihood, maximum parsimony, and neighbor-joining analyses revealed the presence of two well-supported distinct clades corresponding to S. colias and S. japonicus, respectively. Altogether, morphologic and genetic data are in agreement with the recognition of two different species, S. colias in the Atlantic, and S. japonicus in the Pacific.

No abstract

No abstract