New Insights into the Biogeographic and Karyotypic Evolution of Hoplias Malabaricus

Macroevolutionary consequences of karyotypic changes in the neotropical Serrasalmidae fishes (Ostariophysi, Characiformes) diversification

In the Neotropical region, one of the most diverse families of freshwater fishes is the monophyletic Serrasalmidae. Karyotypically, the family shows high diversity in chromosome numbers (2n = 54 to 64). However, little is discussed about whether the chromosomal changes are associated with cladogenetic events within this family. In the present study, we evaluated the role of chromosomal changes in the evolutionary diversification of Serrasalmidae. Our phylogenetic sampling included 36 species and revealed three main clades. The ancestral chromosome number reconstruction revealed the basic number 2n = 54 and a high frequency of ascending dysploid events in the most derived lineages. Our biogeographic reconstruction suggests an Amazonian origin of the family at 48-38 Mya, with independent colonization of other basins between 15 and 8 Mya. We did not find specific chromosomal changes or increased diversification rates correlated with the colonization of a new environment. On the other hand, an increase in the diversification rate was detected involving the genus Serrasalmus and Pygocentrus in the Miocene, correlated with the stasis of 2n = 60. Our data demonstrate that chromosomal rearrangements might have played an important evolutionary role in major cladogenetic events in Serrasalmidae, revealing them as a possible evolutionary driver in their diversification.

DNA barcoding and phylogeography of the Hoplias malabaricus species complex

Hoplias malabaricus (Bloch, 1794) is a carnivorous fish species widely distributed from northern to southern South America. This taxon is believed to be a good model for the investigation of biogeographic events that shape the ichthyofauna evolution in the Neotropical freshwater systems. However, many studies have revealed that H. malabaricus hides a species complex that hampers its taxonomic identity and limit its practical value for evolutionary and biogeographic studies. In this paper, we used the mitochondrial gene cytochrome c oxidase subunit I (COI) to delimit cryptic species and explore the phylogeography of H. malabaricus sensu stricto. We found genetic evidence for putative new species in the genus Hoplias and showed that H. malabaricus (Bloch, 1794) is a major clade assigned to barcode index number (BIN) BOLD:ABZ3047. This species is structured in six subpopulations differentiated by high Fst values and restricts gene flow. The subpopulations of the São Francisco/East Atlantic/Eastern Northeast Atlantic/Parnaíba/Itapecuru River basins and Tapajós River Basin were the most differentiated and showed demographic fluctuations. The present distributional pattern is most likely explained through a scenario from the Pleistocene.

DNA Barcoding unveils cryptic lineages of Hoplias malabaricus from Northeastern Brazil

The trahira or wolf fish - Hoplias malabaricus- is a valid species, although recent cytogenetic and molecular studies have indicated the existence of a species complex. In this context, the present study analyzed the mitochondrial COI marker to determine the levels of genetic diversity of specimens from the Brazilian state of Maranhão, and verify the occurrence of distinct lineages within the study area. Samples were collected from the basins of the Turiaçu, Pindaré, Mearim, Itapecuru, and Parnaíba rivers. A 630-bp fragment was obtained from 211 specimens, with 484 conserved and 108 variable sites, and 60 haplotypes (Hd = 0,947; π = 0,033). The phylogenetic analyses indicated the existence of three distinct lineages of H. malabaricus from Maranhão. Genetic distances of 1.5-8.2% were found between all the populations analyzed, while the variation between haplogroups ranged from 2.1% to 7.7%. The AMOVA indicated that most of the molecular variation was found among groups, with high FST values. The high levels of genetic variability found in the present study are supported by the available cytogenetic data. These findings reinforce the need for the development of effective programs of conservation and management independently for each river basin, in order to preserve the genetic variability found in this taxon.

Integrative taxonomy reveals disjunct distribution and first record of Hoplias misionera (Characiformes: Erythrinidae) in the Amazon River basin: morphological, DNA barcoding and cytogenetic considerations

Abstract The Hoplias malabaricus group encompasses six valid species and still is believed to harbors cryptic diversity. In this work, an integrative approach including morphological, DNA barcoding, and cytogenetic considerations was conducted to characterize a population of H. malabaricus from the Amazon basin that was recently allocated in the same mitochondrial lineage with H. misionera, a species originally described from La Plata basin. The DNA barcoding analysis revealed that the Amazon population nested together with H. misionera specimens from the La Plata basin (BIN AAB1732) in the same cluster. The intragroup distance (0.5%) was 12 times lower than the nearest neighbor (6%) distance. The morphometric analysis demonstrated slightly variation between Amazon and La Plata populations, being the former composed by larger specimens. Further morphological data supported the molecular evidence of H. misionera inhabiting Amazon basin. The karyotype characterization of H. misionera in the Amazon population showed 2n=40 and karyotypic formulae 20m+20sm, that added to C-banding, Ag-NOR and 18S results are suggestive of the similarity to karyomorph C of H. malabaricus. This work reveals the first record of H. misionera outside of La Plata basin and expands the species distribution for 2500 km northward until the Marajó Island, estuary of Amazonas River.

Karyotypic Comparison of Hoplias malabaricus (Bloch, 1794) (Characiformes, Erythrinidae) in Central Amazon

Hoplias malabaricus comprises seven karyomorphs (A-G) and evolutionary units have been described in some of them. In this study, the karyotypic composition and genomic organization of individual H. malabaricus from Central Amazon are described and to verify whether they can be classified according to known karyomorphs. Individuals from the Ducke Reserve have 2n = 42 chromosomes, similar to karyomorph A. Individuals from Catalão Lake and Marchantaria Island exhibit 2n = 40 chromosomes, similar to karyomorph C. Regarding the constitutive heterochromatin, individuals from all locations present centromeric/pericentromeric blocks, in addition to some bitelomeric and interstitial markings. The number of chromosomes with nucleolar organizer region, 5S rDNA and 18S rDNA sites varied among the different locations. The Rex 3 element has a compartmentalized distribution at the terminal and centromeric regions of most chromosomes, with subtle differences among populations. Fluorescence in situ hybridization performed with a telomeric probe allowed the detection of these regions only at the terminal ends of the chromosomes. Thus, only the chromosomal macrostructure (karyomorphs A-G) is not sufficient to establish evolutionary units within the H. malabaricus group, considering differences in the genome organization that are found among their populations. Such differences in the genomic organization could be mainly caused by the sedentary habits of this species.

Cytogenetic characterization of Hoplias malabaricus (Bloch, 1794) from the Ctalamochita River (Córdoba, Argentina): first evidence for southernmost populations of this species complex and comments on its biogeography

Hoplias malabaricus (Bloch, 1794), a predatory freshwater fish with a wide distribution throughout South America, represents a species complex with seven well characterized karyomorphs at the cytogenetic level. Although this species has been extensively studied in several Brazilian basins, data are still scarce for hydrographic systems from other South American countries. This study aims to characterize cytogenetically the Hoplias malabaricus populations from the Argentinean Central Region, close to the southernmost distribution of this species complex. A total of 32 specimens from the Ctalamochita River, a tributary of Lower Paraná Basin located in the province of Córdoba, were analyzed using cytogenetic techniques (Giemsa staining, C- and Ag-NOR banding and fluorescent in situ hybridization with 18S rDNA). All the specimens showed diploid number 2n=42, chromosomic formula 22m + 20sm and absence of sexual chromosomes. Thus, the analyzed populations belong to the karyomorph named A. These populations showed a remarkable degree of divergence in their cytogenetic traits such as karyotypic formula, C-banding, NORs and 18S rDNA patterns for Hoplias malabaricus from other populations bearing the same karyomorph in the Middle and Upper Paraná Basin. These findings are consistent with molecular data from a recent study (where specimens collected in the present work were included), which indicate a closer phylogenetic relationship of Hoplias malabaricus populations from the Ctalamochita River with those from the Uruguay basin and the coastal regions of South Brazil than with populations from the Middle and Upper Paraná Basin. Overall, these pieces of evidence highlight the distinctive features of Hoplias malabaricus from the Ctalamochita River, and also reveal a complex history of dispersion of these populations. The present work is the first to provide cytogenetic information and include some phylogeographic aspects of Hoplias malabaricus populations living in close proximity to the southernmost extreme of its distribution area. Therefore, this study expands significantly upon the previously known geographical coverage for karyomorph A and contributes to a better understanding of the karyotypic diversification within this species complex.

Genotoxic and mutagenic evaluation of water samples from a river under the influence of different anthropogenic activities

Pollution of aquatic ecosystems is associated with the discharge of mostly industrial and urban effluents, which may cause loss of biodiversity and damage to public health. This study aims to evaluate the toxicity and mutagenicity of water samples collected in the Corrente River, a major waterway in the river basin district of Pedro II, Piauí (Brazil). This river is exposed to intense anthropogenic influence from urban, automotive mechanical and family farm waste, and it is used as the main source of water supply by the population. Water samples were collected during the rainy and dry seasons, at four sites in the Corrente River, and evaluated by physicochemical, microbiological and inorganic elements analyses. The samples were evaluated for mutagenicity using the Allium cepa test (toxicity, chromosomal aberration and micronucleus tests) and fish (Tilapia rendalli and Hoplias malabaricus). The physicochemical, microbiological and inorganic results show a large contribution to the pollution loads at collection points in the town of Pedro II, demonstrating the influence of urban pollution. The Al, Si, Ti, Cr, Ni and Cu contents were determined by PIXE. These same Corrente River water samples demonstrated mutagenic effect for A. cepa and fish, as well as toxicity in the A. cepa test. The observations of mutagenic effect may suggest that the complex mixture of agents is comprised of both clastogenic and aneugenic agents. This study also showed the need for constant monitoring in places with environmental degradation caused by urban sewage discharges.