Terumi Hatanaka

Mapping of the 18S and 5S ribosomal RNA genes in the fish Prochilodus argenteus Agassiz, 1829 (Characiformes, Prochilodontidae).

A single NOR-bearing chromosome pair was identified by silver nitrate staining in a previous study of the fish Prochilodus argenteus from the S ã o Francisco River (MG, Brazil), with a third metacentric chromosome sporadically bearing active NOR. The present study focused on an analysis of the chromosomal localization of both the major (45S) and the minor (5S) rRNA genes using FISH. The use of the 18S rDNA probe confirmed the previous Ag-NOR sites interstitially located in a large metacentric pair and also identified up to three other sites located in the telomeric regions of distinct chromosomes, characterizing an interindividual variation of these sites. In addition, the 5S rDNA site was revealed adjacent to the major NOR site, identified at the end of the large Ag-NOR bearing metacentric chromosome. In a few metaphases, an additional weak hybridization signal was observed in a third chromosome, possibly indicating the presence of another 5S rDNA cluster. Despite a lower karyotype diversification (2n=54 and FN=108) often observed among species of Prochilodontidae, variations involving both 45S and 5S rRNA genes could play an important role in their chromosome diversification.

RAPD markers indicate the occurrence of structured populations in a migratory freshwater fish species

Many factors have contributed to the destruction of fish habitats. Hydroelectric dams, water pollution and other environmental changes have resulted in the eradication of natural stocks. The aim of this study was to detect the genetic variation in Prochilodus marggravii from three collection sites in the area of influence of the Tres Marias dam (MG) on the Sao Francisco river (Brazil), using the RAPD technique. The results obtained revealed that the fish in the downstream region nearest the dam have a higher similarity coefficient than those from the other sampling sites that may be related to differences in environmental characteristics in these regions. Additionaly, significant differences in the band frequencies were observed from one collection site to another. These both findings suggest the occurrence of a structured population and have important implications for the conservation of the genetic variability of distinct natural P. marggravii stocks.

Population Substructuring in a Migratory Freshwater Fish Prochilodus argenteus (Characiformes, Prochilodontidae) from the São Francisco River

The construction of hydroelectric dams, pollution of rivers and other environmental changes are responsible for the disappearance of many natural fish stocks. The purpose of this work was to analyze the fish Prochilodus argenteus inhabiting the region of the Três Marias dam in the São Francisco River (Brazil) collected in two sites having distinct environmental characteristics. Three novel homologous and one known cross-specific microsatellites were used to assess genetic variation within and between the two collection sites (namely A and B) in order to confirm the occurrence of population substructuring previously suggested using RAPD markers. A higher number of exclusive alleles and a greater genetic variability in region B strongly reinforce the co-existence of different reproductive units in this area. FST estimates showed a significant population differentiation between the two sites, indicating the possible existence of distinct gene pools. Considering the economic importance of this fishery resource in the São Francisco River, these findings could provide very important information for fisheries management, aquaculture and conservation of the stocks of this species.

Evidence of lack of population substructuring in the Brazilian freshwater fish Prochilodus costatus

Curimbata-pioa (Prochilodus costatus Valenciennes, 1850) is an endemic species from the Sao Francisco River Basin with migratory habits, important ecological role in the ecosystem and relevant fishing importance. The present study aimed to assess the genetic variation in P. costatus in order to investigate its population genetic structure. Genetic variation was studied at three sites downstream the Tres Marias dam (Upper-middle Sao Francisco River, State of Minas Gerais) through six specific microsatellite loci. Fish from the three sites had quite similar genetic diversity levels and no genetic differentiation was detected, suggesting that P. costatus might represent a single reproductive unit in the studied area. Alternatively, the present study was not able to detect putative coexistent and comigrating populations along the main channel river. Our findings could be very helpful for the management and conservation of this fish.

Contribution of conservation genetics in assessing neotropical freshwater fish biodiversity

Human activities have a considerable impact on hydrographic systems and fish fauna. The present review on conservation genetics of neotropical freshwater fish reveals that DNA analyses have been promoting increased knowledge on the genetic structure of fish species and their response to environmental changes. This knowledge is fundamental to the management of wild fish populations and the establishment of Evolutionary Significant Units capable of conserving genetic integrity. While population structuring can occur even in long-distance migratory fish, isolated populations can show reduced genetic variation and be at greater risk of extinction. Phylogeography and phylogeny have been powerful tools in understanding the evolution of fish populations, species and communities in distinct neotropic environments. Captive fish can be used to introduce new individuals and genes into the wild and their benefits and disadvantages can be monitored through genetic analysis. Understanding how fish biodiversity in neotropical freshwaters is generated and maintained is highly important, as these habitats are transformed by human development and fish communities are increasingly exploited as food sources to sustain a growing human population.

Description of novel microsatellite loci in the Neotropical fish Prochilodus argenteus and cross-amplification in P. costatus and P. lineatus

Prochilodus is one of the most important fish resources of South America, in addition to the important role it plays in nutrient cycling of Neotropical rivers. In the present study, we describe the isolation and characterization of nine novel microsatellite loci in Prochilodus argenteus. The number of alleles per polymorphic locus varied from 5 (Par76) to 21 (Par85), revealing a total of 116 alleles. The values of observed and expected heterozygosities ranged from 0.629 (Par69) to 0.926 (Par85 and Par86) and from 0.643 (Par66) to 0.931 (Par80), respectively. Furthermore, the ability of these and other previously described microsatellite markers to amplify orthologous loci was tested in two related species, Prochilodus costatus and Prochilodus lineatus. These loci will be useful for studies of population genetic structure in this group of fishes, and in aiding future genetic mapping studies of P. argenteus.

Genetic population structure of two migratory freshwater fish species (Brycon orthotaenia and Prochilodus argenteus) from the São Francisco River in Brazil and its significance for conservation

Previous genetic studies conducted with migratory fish populations from downstream of the Tres Marias dam in the Sao Francisco River Basin (Brazil) have documented the occurrence of population structuring, as reported for Brycon orthotaenia and Prochilodus argenteus, two commercially important species in this basin. We revisited the genetic structure of these species using microsatellites. B. orthotaenia was sampled during the spawning season and was analyzed using five heterologous microsatellites. P. argenteus was collected in the non-reproductive season and genetic analysis was conducted using ten species- specific microsatellites. For both species, genetic diversity between collection sites was similar. Considering B. orthotaenia, FST and RST estimates and the Bayesian analysis demonstrated significant differences between sites. Two well-defined populations were identified in the study area, indicating population structuring for this species. No significant differences were found for P. argenteus. These data provide information for knowledge regarding genetic structure of migratory fish species, which may contribute toward the conservation besides the understanding the biology and ecology of these important fishery resources.

Microsatellite loci isolated from the lowland tapir (Tapirus terrestris), one of the largest Neotropical mammal

We describe ten microsatellite loci from the lowland tapir (Tapirus terrestris), one of the last members of the Neotropical megafauna and considered a vulnerable species. A total of 74 alleles were detected, ranging from four to thirteen alleles per locus. The expected heterozygosity ranged from 0.34 to 0.88, with a mean of 0.635. All but one locus conformed to the Hardy–Weinberg expectations. These microsatellite loci can be used in population genetic studies of the genus Tapirus, in which all species are threatened globally.

Heterochromatin heterogeneity and chromosome heteromorphism in Cerdocyon thous (Mammalia, Canidae)

Os estudos citogeneticos em canideos sul-americanos, de uma forma geral, sao raros. Cerdocyon thous e um representante da familia Canidae e habita florestas, matas abertas e savanas da america do Sul. O seu cariotipo e formado por uma grande proporcao de cromossomos metacentricos e submetacentricos quando comparado com outras especies desta familia e possui tambem uma grande quantidade de heterocromatina constitutiva, especialmente ao longo do braco curto dos cromossomos submetacentricos. No presente estudo, diferentes metodos de bandamentos cromossomicos permitiram verificar o carater heterogeneo dos grandes segmentos heterocromaticos e a proposicao de um modelo de organizacao deste segmento que ocupa todo o braco curto da maioria dos cromossomos de dois bracos. Alem disso, e descrito um heteromorfismo cromossomico relacionado ao braco curto de um grande cromossomo submetacentrico, equivalente ao no. 3 do cariotipo de animais de ambos os sexos.

Early Stages of XY Sex Chromosomes Differentiation in the Fish Hoplias malabaricus (Characiformes, Erythrinidae) Revealed by DNA Repeats Accumulation

Background: Species with ‘young’ or nascent sex chromosomes provide unique opportunities to understand early evolutionary mechanisms (e.g. accumulation of repetitive sequences, cessation of recombination and gene loss) that drive the evolution of sex chromosomes. Among vertebrates, fishes exhibit highly diverse and a wide spectrum of sex-determining mechanisms and sex chromosomes, ranging from cryptic to highly differentiated ones, as well as, from simple to multiple sex chromosome systems. Such variability in sex chromosome morphology and composition not only exists within closely related taxa, but often within races/populations of the same species. Inside this context, the wolf fish Hoplias malabaricus offers opportunity to investigate the evolution of morphologically variable sex chromosomes within a species complex, as homomorphic to highly differentiated sex chromosome systems occur among its different karyomorphs. Materials & Methods: To discover various evolutionary stages of sex chromosomes and to compare their sequence composition among the wolf fish´s karyomorphs, we applied multipronged molecular cytogenetic approaches, including C-banding, repetitive DNAs mapping, Comparative Genomic Hybridization (CGH) and Whole Chromosomal Painting (WCP). Our study was able to characterize a cryptically differentiated XX/XY sex chromosome system in the karyomorph F of this species. Conclusion: The Y chromosome was clearly identified by an interstitial heterochromatic block on the short arms, primarily composed of microsatellite motifs and retrotransposons. Additionally, CGH also identified a male specific chromosome region in the same chromosomal location, implying that the accumulation of these repeats may have initiated the Y chromosome differentiation, as well as played a critical role towards the evolution and differentiation of sex chromosomes in various karyomorphs of this species.