Karyoevolutionary aspects of Atlantic hogfishes (Labridae-Bodianinae), with evidence of an atypical decondensed argentophilic heterochromatin.

Fish from the family Labridae elicit considerable ecological interest, especially due to their complex interactions with the reef environment. Different karyoevolutionary tendencies have been identified in the subfamilies Bodianinae, Corinae and Cheilinae. Chromosomal analyses conducted in the Atlantic species Bodianus rufus (2n=48; 6m+12sm+14st+16a, FN=80), Bodianus pulchellus (2n=48; 4m+12sm+14st+18a, FN=78) and Bodianus insularis (2n=48; 4m+12sm+14st+18a, FN=78) identified Ag-NOR/18SrDNA sites located only in the terminal region of the short arm (p) of the largest subtelocentric pair. The 5S rDNA genes were mapped in the terminal region of the long arm (q) of the largest acrocentric pair and the p arm of chromosome 19 in B. insularis. The karyotype of the three species shows an extensive heterochromatic and argentophilic region, exceptionally decondensed, located in the p arm of the second subtelocentric pair. This region does not correspond to a NOR site, since it is not hybridized with 18S rDNA probes, and is not GC-rich, as generally occurs with nucleolus organizer regions of lower invertebrates. Heterochromatin in the three species is reduced and distributed over the centromeric and pericentromeric regions of chromosomes. The elevated number of two-armed chromosomes in species of Bodianus, in relation to other Labridae, shows karyotype diversification based on pericentric inversions, differentiating them markedly in terms of evolutionary tendencies that occur in subfamilies Corinae and Cheilininae. Structural cytogenetic similarities between B. pulchellus and B. insularis, in addition to the conserved chromosomal location pattern of ribosomal multigenic families, indicate phylogenetic proximity of these species.

Robertsonian rearrangements and pericentric inversions in Scaridae fish (Perciformes).

The parrotfishes (family Scaridae) are comprised of the subfamilies Sparisomatinae and Scarinae. They are important agents of marine bioerosion, which rework the substrate with their beaklike jaws. Despite their importance, there are no published cytogenetic data on this group. We made cytogenetic analyses of Sparisoma axillare (Sparisomatinae) and Scarus trispinosus [corrected] (Scarinae) from the Brazilian coast. Differentiation in the diploid number in S. axillare compared to the basal karyotype of the Perciformes apparently occurred due to a Robertsonian fusion, combined with pericentric inversions. S. trispinosus [corrected] presented a conserved diploid number, but showed considerable structural karyotypic changes, resulting mainly from pericentric inversions. The Ag-NOR sites were unique and located on the short arm of the 1st subtelocentric pair in both species (possibly homeologous), corresponding to the 11th pair in S. axillare and the 9th pair in S. trispinosus [corrected] The constitutive heterochromatin is reduced in these species and is distributed in centromeric and pericentromeric regions in most of the chromosomes. The low fundamental number compared to the Scarus genus suggests a more basal condition for Sparisoma. The chromosome formula in S. trispinosus [corrected] was more diversified, deriving from large-scale pericentric inversions. Karyotypic evolution patterns observed for these representatives of the Sparisomatinae and Scarinae subfamilies, added to new data from a larger number of species, would allow us to determine if there is a tendency among the Sparisomatinae for centric fusion events.

Robertsonian rearrangements and pericentric inversions in Scaridae fish (Perciformes)

The parrotfishes (family Scaridae) are comprised of the subfamilies Sparisomatinae and Scarinae. They are important agents of marine bioerosion, which rework the substrate with their beaklike jaws. Despite their importance, there are no published cytogenetic data on this group. We made cytogenetic analyses of Sparisoma axillare (Sparisomatinae) and Scarus coelestinus (Scarinae) from the Brazilian coast. Differentiation in the diploid number in S. axillare compared to the basal karyotype of the Perciformes apparently occurred due to a Robertsonian fusion, combined with pericentric inversions. S. coelestinus presented a conserved diploid number, but showed considerable structural karyotypic changes, resulting mainly from pericentric inversions. The Ag-NOR sites were unique and located on the short arm of the 1st subtelocentric pair in both species (possibly homeologous), corresponding to the 11th pair in S. axillare and the 9th pair in S. coelestinus. The constitutive heterochromatin is reduced in these species and is distributed in centromeric and pericentromeric regions in most of the chromosomes. The low fundamental number compared to the Scarus genus suggests a more basal condition for Sparisoma. The chromosome formula in S. coelestinus was more diversified, deriving from large-scale pericentric inversions. Karyotypic evolution patterns observed for these representatives of the Sparisomatinae and Scarinae subfamilies, added to new data from a larger number of species, would allow us to determine if there is a tendency among the Sparisomatinae for centric fusion events.