Cytogenetic studies in Brazilian marine Sciaenidae and Sparidae fishes (Perciformes)

Fishes from the families Sciaenidae and Sparidae, the former comprising coastal species associated with shallow waters on the continental shelf and the latter composed of typically marine species, are of significant economic value. Karyotypic data are available for about 20% of the total number of species in these groups. In the present study, cytogenetic analyses were carried out in three Sciaenidae species, Menticirrhus americanus, Ophioscion punctatissimus and Pareques acuminatus, as well as in the sparid fish, Archosargus probatocephalus, using conventional staining (Giemsa) and Ag-nucleolar organizer regions (NORs) and C-banding techniques. The diploid values (2n) and number of chromosome arms were equal to 48 in all species analyzed. NORs were located at pericentromeric positions, equivalent to large heterochromatic blocks, in M. americanus (1st pair), O. punctatissimus (10th pair), P. acuminatus (2nd pair), and A. probatocephalus (3rd pair). Heterochromatin was detected at the centromeric position in most chromosome pairs, being more conspicuous among Scianidae members. The remarkable karyotypic conservativeness detected in these species is similar to that observed in other perciform groups previously studied, regarding both the number of acrocentric chromosomes and NOR location. However, unusual events of heterochromatinization seem to have taken place along the karyotypic evolution of members of the family Sciaenidae. For the family Sparidae, distinct cytotypes between samples of Northeast Brazil and those previously analyzed on the southeastern coast were identified, suggesting that putative biogeographic barriers could be present throughout both regions on South Atlantic coast.

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.

Lack of interpopulation genetic structure in the genus Stegastes (Perciformes) with indication of local introgression

The family Pomacentridae comprises about 326 species belonging to 28 genera. The genus Stegastes is composed of nearly 33 species, and 8 are endemic to the Brazilian Province, inhabiting the Brazilian coast (Stegastes fuscus, S. variabilis, S. leucosticus, S. uenfi, and S. pictus) or Western Atlantic oceanic islands (S. trindadensis, S. rocasensis and S. sanctipauli). Stegastes species play a major role in the reef ecosystem since they interfere significantly with the composition of benthonic organisms. Studies about population genetics and speciation of Neotropical ichthyofauna are scarce, particularly at insular areas from the Western Atlantic. Random amplified polymorphic DNA markers were used to analyze the population genetic structure of the continental species S. fuscus and S. variabilis (Northeastern Brazil) as well as the insular species S. sanctipauli (Saint Paul’s Rocks). Analysis of population parameters revealed a high index of intrapopulation genetic variability in the species, except for S. sanctipauli, which showed low values. The phiST values in samples of S. fuscus and S. variabilis obtained at distinct collection sites 35 km apart from each other indicated a lack of population genetic structure. An intermediary profile of species-specific markers was detected in some individuals of S. fuscus and S. variabilis from Santa Rita, Rio Grande do Norte, suggesting a putative introgression event between the two species. The genetic profiles observed in Stegastes populations indicate a higher genetic variability along the shoreline than at oceanic sites, related to a reduced effective population size on islands. The lack of genetic differentiation among coastal populations suggests that, despite some biological features such as non-migratory behavior and territoriality, the pelagic larval phase of these species is able to promote an interpopulation homogeneity among sampled areas.