Simoni Santos

Population genetic structuring of the king weakfish, Macrodon ancylodon (Sciaenidae), in Atlantic coastal waters of South America: deep genetic divergence without morphological change

Phylogeographic patterns in Macrodon ancylodon sampled from 12 locations across all its range were investigated using mitochondrial DNA cytochrome b sequences, and analysed together with patterns of morphometric differentiation. Populations of the North Brazil and the Brazil currents, with warmer waters, form a clade (tropical clade) separated by 23 fixed mutations from the populations that inhabit regions of colder waters influenced by the Brazil and Malvinas currents (subtropical clade). No gene flow exists between the tropical and subtropical clades, and most likely also between the two groups of the tropical clade. Distribution of these clades and groups is correlated with flow of currents and their temperatures, and is facilitated by larval retention and low adult migration. Despite differentiation at the molecular level, fishes analysed from all these current‐influenced regions are morphometrically homogeneous. Throughout its range M. ancylodon inhabits the same, or very similar niche; thus, stabilizing selection probably promotes the retention of highly conserved morphology despite deep genetic divergence at the mitochondrial DNA cytochrome b.

Genetic differentiation of Macrodon ancylodon (Sciaenidae, Perciformes) populations in Atlantic coastal waters of South America as revealed by mtDNA analysis

The king weakfish (pescada-go in Portuguese - Macrodon ancylodon (Sciaenidae), a demersal (bottom-feeding) species found in South America Atlantic coastal waters from the Gulf of Paria in Venezuela to Baia Blanca in Argentina, is an economically important species because of its abundance and wide acceptance by consumers. Because of its wide distribution this fish may be subject to geographic isolation and this may have resulted in distinct populations along its coastal range. Considering that this species represents an important economic resource, confirmation of whether M. ancylodon is a single species or there are different genetic stocks spread over its wide distribution would be an important contribution to conservation policies and population management of the king weakfish. To investigate differences between king weakfish populations we used the cytochrome b and 16S rRNA genes to characterize M. ancylodon specimens caught throughout its South American range from Venezuela to Argentina. Our results clearly distinguished two genetically different groups which show nucleotide divergence and genetic structuring patterns that strongly suggest they may be different species, disagreeing with the widely accepted traditional taxonomy that accepts only one species of Macrodon in the western Atlantic.

Low levels of genetic diversity depicted from mitochondrial DNA sequences in a heavily exploited marine fish (Cynoscion acoupa, Sciaenidae) from the Northern coast of Brazil

The acoupa weakfish (Cynoscion acoupa - Sciaenidae) is a marine species of croaker with estuarine-dependent behavior, found in the western Atlantic from Panama to Argentina. It is one of the most exploited food fish on the northern coast of Brazil. In this study, DNA sequences were determined from the entire control region (D-loop) of the mitochondrial genome of 297 individuals collected during seven different months between December 2003 and August 2005 on the northern coast of Brazil (Amapa and Para). Genetic variability expressed by haplotype (h = 0,892) and nucleotide (p = 0,003) diversities were low compared to other heavily exploited marine fish species from the western Atlantic and eastern Asia. AMOVA depicted a lack of genetic structuring among the samples from different years, indicating the presence of a single stock of C. acoupa within the sample area. The possible reasons for the low levels of genetic diversity are discussed. These results demonstrate a need for the monitoring of C. acoupa harvesting and the preservation of the estuaries within its geographic range, considering that this large fish depends on estuarine ecosystems during part of its life cycle.

Can Lutjanus purpureus (South red snapper) be "legally" considered a red snapper (Lutjanus campechanus)?

Red snappers (Lutjanus purpureus in Brazil and Lutjanus campechanus in USA and Gulf of Mexico) are both under clear effect of overfishing. Because of their high morphological similarity it has already been suggested that they could possibly be considered as a single species. To investigate the degree of similarity and the genetic structure of red snapper populations we constructed a common dataset of partial D-loop mtDNA sequences of L. purpureus from Brazil (Amapa, Para and Maranhao) and L. campechanus from the Atlantic coast of the USA (Florida, Louisiana and Mississippi). Phylogenetic and population genetic analyses surprisingly depicted high similarity between L. campechanus and L. purpureus, compatible with the hypothesis of a single species of red snapper for the Western Atlantic Ocean. These preliminary but very curious findings open an important discussion regarding the legislation involved on the capture of this overexploited fish resources as well as regarding their taxonomy.

Genetic variation in native and farmed populations of Tambaqui (Colossoma macropomum) in the Brazilian Amazon: regional discrepancies in farming systems

The tambaqui, Colossoma macropomum, is the most popular fish species used for aquaculture in Brazil but there is no study comparing genetic variation among native and farmed populations of this species. In the present study, we analyzed DNA sequences of the mitochondrial DNA to evaluate the genetic diversity among two wild populations, a fry-producing breeding stock, and a sample of fish farm stocks, all from the region of Santarém, in the west of the Brazilian state of Pará. Similar levels of genetic diversity were found in all the samples and surprisingly the breeding stock showed expressive representation of the genetic diversity registered on wild populations. These results contrast considerably with those of the previous study of farmed stocks in the states of Amapá, Pará, Piauí, and Rondônia, which recorded only two haplotypes, indicating a long history of endogamy in the breeding stocks used to produce fry. The results of the two studies show two distinct scenarios of tambaqui farming in the Amazon basin, which must be better evaluated in order to guarantee the successful expansion of this activity in the region, and the rest of Brazil, given that the tambaqui and its hybrids are now farmed throughout the country.

Mitochondrial DNA reveals population structuring in Macrodon atricauda (Perciformes: Sciaenidae): a study covering the whole geographic distribution of the species in the southwestern Atlantic.

Abstract We investigated the genetic structure and diversity of M. atricauda, based on 266 specimens collected off the coast of southern Brazil and Argentina at seven locations, covering the whole geographic distribution of this species. A DNA sequence alignment of 904 base pairs of the mitochondrial Control Region revealed a total of 85 haplotypes. FST analyses suggest that M. atricauda does not comprise a single demographic stock. Two different genetic units are identified, which possibly are related to ecological adaptations of the species within its range. Genetic diversity, Bayesian analysis of population structure, and significant negative results for the D and FS tests indicate that M. atricauda populations have undergone recent expansion. The spatial distribution of genetic variation seems to be related to historical colonization from south to north, followed by expansion.

Molecular phylogeny of the western South Atlantic Sciaenidae based on mitochondrial and nuclear data.

Fragments of mitochondrial (COI and rRNA 16S) and nuclear (Tmo-4C4) genes were sequenced to evaluate the phylogenetic relationships among 15 genera of the western South Atlantic Sciaenidae, two freshwater genera and the northwest Pacific Larimichthys crocea. Our results suggest a great diversification for the western Atlantic assemblage; the monophyly of Macrodon, Menticirrhus and Plagioscion genera; the distinctiveness of Bardiella, Stellifer and Ophioscion as belonging to the same clade; the possible existence of two distinct groups in Stellifer; the closer relationship between Lonchurus and Paralonchurus; the non-monophyly of Cynoscion; and the remarkable diversification of Larimus breviceps populations in the Brazilian coast. This is the most comprehensive study evaluating the phylogenetic relationships of the western Atlantic sciaenid and provides a guide for future studies within this family.

Molecular Phylogeny of Weakfish Species of the Stellifer Group (Sciaenidae, Perciformes) of the Western South Atlantic Based on Mitochondrial and Nuclear Data

The phylogenetic relationships within the Stellifer group of weakfishes (Stellifer, Odontoscion, Ophioscion, and Bairdiella) were evaluated using 2723 base pairs comprising sequences of nuclear (rhodopsin, TMO-4C4, RAG-1) and mitochondrial (16S rRNA and COI) markers obtained from specimens of nine species. Our results indicate a close relationship between Bairdiella and Odontoscion, and also that the genus Stellifer is not monophyletic, but rather that it consists of two distinct lineages, one clade containing S. microps/S. naso/S. brasiliensis and the other, S. rastrifer/S. stellifer/Stellifer sp. B, which is closer to Ophioscion than the former clade. The O. punctatissimus populations from the northern and southern Brazilian coast were also highly divergent in both nuclear (0.8% for rhodopsin and 0.9% for RAG-1) and mitochondrial sequences (2.2% for 16S rRNA and 7.3% for COI), which we conclude is consistent with the presence of two distinct species. The morphological similarities of the members of the Stellifer group is reinforced by the molecular data from both the present study and previous analyses, which have questioned the taxonomic status of the Stellifer group. If, on the one hand, the group is in fact composed of four genera (Stellifer, Ophioscion, Odontoscion, and Bairdiella), one of the two Stellifer clades should be reclassified as a new genus. However, if the close relationship and the reduced genetic divergence found within the group is confirmed in a more extensive study, including representatives of additional taxa, this, together with the morphological evidence, would support downgrading the whole group to a single genus. Obviously, these contradictory findings reinforce the need for a more systematic taxonomic revision of the Stellifer group as a whole.

Molecular Phylogenetic and Population Genetic Structuring of Macrodon sp., a Coastal and Estuarine Fish of the Western Atlantic Ocean

The study on fish fauna of the Caete estuary led to a large-scale phylogenetic analysis of one of its common fish species, Macrodon ancylodon. Phylogeographic patterns in M. ancylodon sampled from 16 locations in the subtropical and tropical western Atlantic Ocean were investigated using mitochondrial DNA 16S rRNA and cytochrome b sequences. The analysis shows two monophyletic and highly differentiated lineages of Macrodon populations in the western Atlantic Ocean, and there was no zone of overlap between the two groups, which were geographically separated in the region of South Bahia (Porto Seguro) and north Espirito Santo (Vitoria). Tropical and subtropical groups of Macrodon show nucleotide divergences for the 16S gene varying from 2.4 to 3.5%, a magnitude of genetic divergences usually observed between distinct species of Sciaenidae. The high values of divergence observed between the two groups, coupled with the clearly geographic isolation between them, strongly support our conclusions that these groups should be considered distinct species, M. ancylodon (Bloch and Schneider 1801) being the species of the tropical region (Venezuela to Bahia) and Macrodon sp. the new species of the subtropical region (Espirito Santo to Argentina). Curiously, assuming a constant rate of 1% of divergence per million years for the 16S rRNA, estimation obtained by the comparison of Panama trans-isthmian geminate species of Centropomus, we estimate that the separation between the tropical and subtropical groups of Macrodon have possibly occurred between 2.4 and 3.5 million years ago, during the late Pliocene. These genetic evidences strongly indicate a taxonomic revision of this estuarine-dependent group of fishes.

Phylogeny of the subfamily Stelliferinae suggests speciation in Ophioscion Gill, 1863 (Sciaenidae: Perciformes) in the western South Atlantic

Phylogenies based on morphological and molecular data confirm the monophyly of the subfamily Stelliferinae; however, there is no consensus on the intergeneric and interspecific relationships in the group. Previous studies suggested the non-monophyly of Ophioscion and Stellifer, and possible cryptic species in Ophioscion punctatissimus. Therefore, we used mitochondrial (16S rDNA and COI) and nuclear (Rhodopsin, EGR1, and RAG1) regions to examine phylogenetic relationships among species of this subfamily. Our results confirmed the monophyly of Stelliferinae and supports the close relationship among Bardiella, Corvula and Odontoscion, which form a sister group to Stellifer and Ophioscion. Notwithstanding, all the results support the non-monophyly of Stellifer and Ophioscion and we suggest that a taxonomic revision should consider Ophioscion as a junior synonym of Stellifer. Moreover, O. punctatissimus was grouped into two clades, with the O. punctatissimus lineage I (LI) being closer to O. scierus from the eastern Pacific than to the O. punctatissimus lineage II (LII). The most recent common ancestor (TMRCA) for the O. scierus and O. punctatissimus LI and O. punctatissimus LII clade dates from 7.2 (HPD: 4.3-10.5) Ma, whereas TMRCA for the O. scierus and O. punctatissimus LI clade dates from 5.3 (HPD: 2.4-8.6) Ma, indicating that speciation processes may be related to the rise of the Isthmus of Panama. Phylogeographic analyses corroborate the hypothesis of speciation in O. punctatissimus. These results suggest that lineages of O. punctatissimus originated from distinct ancestors and, by morphological similarity, were considered the same taxon. A taxonomic revision should be performed to validate the species status of such lineages.