Ecologia de Astyanax taeniatus na Bacia do Rio Mato Grosso, Saquarema - RJ: Dieta, uso do micro-hábitat e uma breve análise comportamental

Neste trabalho tivemos como objetivo caracterizar a dieta, uso do habitat e padrões comportamentais de Astyanax taeniatus da bacia do Rio Mato Grosso, que encontra-se na porção leste do Estado do Rio de Janeiro (22 52 S; 42 40 W e 22 53 S; 42 34 W). Para a análise da dieta, os exemplares foram coletados bimestralmente entre março de 2006 e janeiro de 2007 em três localidades que diferiram pelas variáveis físicas. As observações de uso dos recursos do habitat foram realizadas por observação subaquática, na posição focal dos exemplares avistados, enquanto a quantificação da disponibilidade foi realizada em 50 quadrats de 20x20cm (400cm2) ao longo dos mesmos 50m onde foi realizada a observação sub-aquática. A análise do conteúdo estomacal de 651 exemplares foi realizada sob microscópio estereoscópico de acordo com métodos qualitativos e quantitativos (Freqüência de Ocorrência e Volumétrica). A participação relativa de cada item registrado nos estômagos em relação à totalidade da dieta foi analisada através do Índice Alimentar (IAi). Para verificar possíveis diferenças entre as proporções dos itens de origem animal e vegetal, autóctone e alóctone, os valores proporcionais foram testados pelo 2 de contingência. A partir dos dados de comprimento padrão e comprimento do intestino, foi calculado o valor do quociente intestinal. Os itens de origem vegetal tiveram maior contribuição na dieta da espécie para as localidades com maior altitude, enquanto os itens animais tiveram maior contribuição na localidade baixa. A diferença na contribuição dos itens de origem autóctone e alóctone também foi significativa. Na dieta de jovens e adultos, houve diferença significativa na contribuição de itens de origem vegetal e animal somente na localidade mais alta, onde os adultos consumiram maior quantidade de matéria vegetal. Os valores médios de quociente intestinal em jovens e adultos foram significativamente diferentes nas localidades de maior altitude, com valores maiores para indivíduos adultos. Observamos 52% dos indivíduos em profundidades entre 30 e 45 cm, 72% em áreas de rápido, 72% em velocidades entre 0 e 0,5km/h, 66% encontravam-se distantes da margem entre 40 e 120 cm, 37,6% em substrato do tipo areia e 34,4% em substrato do tipo pedra. De todos os padrões comportamentais observados, aquele que mais se destacou foi o forrageamento, onde 70,91% dos indivíduos estavam forrageando no meio da coluna dágua. Os resultados da dieta reforçam a idéia de as espécies de Astyanax têm hábito alimentar onívoro e oportunista, onde a espécie alimentou-se dos recursos disponíveis no ambiente evidenciando sua alta plasticidade alimentar ao longo do riacho. Espécies do gênero Astyanax são consideradas generalistas em relação ao uso do habitat e altamente ativas, corroborando com os resultados do presente estudo.

Comparative Cytogenetics and Molecular Phylogeography in the Group Astyanax altiparanae - Astyanax aff. bimaculatus (Teleostei, Characidae)

The genus Astyanax comprises small characin fish of the neotropical region. The so-called `yellow-tailed characins` compose one of the most widely distributed Astyanax groups. A. altiparanae and A. aff. bimaculatus, are evolutionarily closely related and commonly found in several Brazilian hydrographic basins. In the present work, chromosomal data of specimens of A. altiparanae and A. aff. bimaculatus from 4 hydrographic basins in the states of Sao Paulo (Upper Tiete, Paranapanema, Ribeira de Iguape) and Rio de Janeiro (Guapimirim) are shown. All the populations showed 50 chromosomes, with different karyotypic formula. Although only a single Ag-NOR bearing chromosome pair was observed, all populations possess multiple cistrons of 18S rDNA. FISH with the 5S rDNA probe showed single signals at the interstitial position of one metacentric chromosome pair. C-bands are distributed in the terminal and interstitial regions of several chromosomes. However, the As-51 satDNA are frugally located in a few chromosomes of fishes from Upper Tiete, Paranapanema and Guapimirim Rivers, being absent in individuals of A. aff. bimaculatus from Ribeira de Iguape River basin. Beside these 4 populations, molecular phylogeography studies were also performed in individuals from Middle and Lower Tiete River basin and from 2 additional collection sites in the Paranapanema and Ribeira de Iguape River basins. The phylogeographic analysis using 2 mtDNA regions (totalizing 1.314 bp of ND2 and ATPase6/8 genes) of 8 populations of the group of `yellow-tailed characins` from 3 major hydrographic basins showed structuring of populations, suggesting a correlation between chromosomal (nuclear) and molecular (mitochondrial) data. Copyright (C) 2011 S. Karger AG, Basel

Astyanax bockmanni Vari and Castro, 2007: an ambiguous karyotype in the Astyanax genus

Despite the widespread distribution of Astyanax bockmanni in streams from Upper Parana River system in central, southeastern, and southern Brazil, just recently, it has been identified as a distinct Astyanax species. Cytogenetic studies were performed in two populations of this species, revealing conservative features. A. bockmanni shows 2n = 50 chromosomes, a karyotypic formula composed of 10 M + 12SM + 12ST + 16A and multiple Ag-NORs. Eight positive signals in subtelocentric/acrocentric chromosomes were identified by fluorescent in situ hybridization (FISH) with 18S rDNA probes. After FISH with 5S rDNA probes, four sites were detected, comprising the interstitial region of a metacentric pair and the terminal region on long arms of another metracentric pair. Little amounts of constitutive heterochromatin were observed, mainly distributed at distal region in two chromosomal pairs. Additionally, heterochromatin was also located close to the centromeres in some chromosomes. No positive signals were detected in the chromosomes of A. bockmanni by FISH with the As-51 satellite DNA probe. The studied species combines a set of characteristics previously identified in two different Astyanax groups. The chromosomal evolution in the genus Astyanax is discussed.

The species complex Astyanax fasciatus Cuvier (Teleostei, Characiformes) - a multidisciplinary approach

Cytogenetic data have provided important clues that the Astyanax fasciatus populations from the Upper Parana River basin could be a part of a more diverse fish group, usually included on the same taxa. Samples collected in Cachoeira de Emas, SP, in Mogi-Guacu River basin, show two major cytotypes presenting 2n = 46 and 2n = 48 chromosomes, with distinct karyotypic formula, despite the fact that the molecular data suggested some degree of gene flow between these cytotypes. Cytogenetic and morphometric analyses were performed in this species, aiming to contribute to the understanding of the natural history from such fish group. Two allopatric populations with distinct standard cytotypes were analysed, and the data obtained suggest the separation into two groups. (c) 2008 The Authors Journal compilation (c) 2008 The Fisheries Society of the British Isles.

Chromosome polymorphism in Astyanax fasciatus (Teleostei, Characidae). 2-Chromosomal location of a satellite DNA

Studies about composition of repetitive sequences and their chromosomal location have been helpful to evolutionary studies in many distinct organisms. In order to keep on assessing the possible relationships among different cytotypes of Astyanax fasciatus (Teleostei, Characiformes) in the Mogi-Guacu River (Sao Paulo State, Brazil), C-banding, chromomycin A 3 staining, and fluorescent in situ hybridization with a repetitive DNA sequence (As51) isolated from Astyanax scabripinnis were performed in the present work. The constitutive heterochromatin was distributed in terminal regions on long arms of submetacentric, subtelocentric, and acrocentric chromosomes and in the terminal region on short arms of a pair of submetacentric chromosomes in both standard cytotypes. This latter heterochromatic site was also GC-rich, as revealed by chromomycin A(3) staining, corresponding to the nucleolar organizer region (NOR), as shown by previous studies. The sites of the satellite As51 DNA were located in terminal regions on long arms of several chromosomes. Some variant karyotypic forms, which diverge from the two standard cytotypes, also presented distinctive chromosomes carrying As51 satellite DNA. It is possible that the standard 2n = 46 cytotype represents an invader population in the Mogi-Guacu River able to interbreed with the resident standard 2n = 48 cytotype. Therefore, the variant karyotypes would be related to a possible viable offspring, where complementary chromosomal rearrangements could favor new locations of the satellite DNA analyzed. Copyright (C) 2008 S. Karger AG, Basel

Ecologia alimentar e reprodutiva da piaba-do-rabo-amarelo, Astyanax cf. lacustris (Reinhardt, 1874) (Osteichthyes: Characidae) na Lagoa do Piató, Assu, Rio Grande do Norte, Brasil

The feeding habits and biological aspects of the reproductive cycle of two-spot astyanax, Astyanax cf. lacustris (Reinhardt, 1874) were investigated. Fish samples were captured on a monthly basis, using gillnets of 4 cm mesh size, from the Piató Lake, Assu, Rio Grande do Norte, during the period of September, 2006 to August, 2007. Physico-chemical parameters, such as, temperature, electrical conductivity and dissolved oxygen of the lake were registered. The monthly values of rainfall also were obtained. The 360 individuals captured, were measured, weighed, dissected, and stomach weight and the stage of gonadal maturity were registered. The stomach contents analyses were carried out based on volumetric method, points, frequency of occurrence and applying the Index of Relative Importance. The degrees of repletion of the stomachs were determined besides the Index of Repletion relating to feeding activity variations and frequency of ingestion with limnological parameters and rainfall. The food items identified were separated into distinct groups according to their origin. Sex ratio and Gonadosomatic Relation of females were verified to determine the spawning period and fecundity. The physico-chemical parameters presented the following annual mean values: temperature = 28.8ºC, electrical conductivity = 992.5 µS.cm-1; dissolved oxygen = 4.9 mg.L-1 during the study period. The annual mean of the rainfall was 63.5 mm. The results indicate that this species present an omnivorous feeding habit with a tendency towards insectivory, with an increase in feeding activity during the dry season. The aquatic oxygen to interfere very importance in the feeding activity than the others factors physico-chemicals of water and rainfall. There was a predominance of females, with a sex proportion of 1M:7F. The macroscopic characteristics of the ovaries and testicles revealed four stages of gonadal development: immature, maturing, mature and spent. A temporal variation was observed for the gonadal development of males and females. There was reproductive activity through out the year, with peaks in the months of February, April and June to correspond with the rain of precipitation of the region. The mean fecundity was 7.681 mature oocytes, varying from 4.476 to 12.036, with mean of 7.681. There was positive relation between fecundity and body mass. Condition Factor is not an efficient indicator of the reproductive period of this species. The species A. cf. lacustris is an opportunist and is well adapted to the conditions of the semi-arid Caatinga Biome

Structural and functional evidence that a B chromosome in the characid fish Astyanax scabripinnis is an isochromosome

Astyanax scabripinnis possesses a widespread polymorphism for metacentric B chromosomes as large as the largest chromosome pair in the A complement. on the basis of C-banding pattern, it was hypothesized that these B chromosomes are isochromosomes that have arisen by means of centromere misdivision and chromatid nondisjunction. In the present paper we test this hypothesis by analysing (i) the localization of a repetitive DNA sequence on both B chromosome arms, and (ii) synaptonemal complex formation, in order to test the functional homology of both arms. Genomic DNA digested with KpnI and analysed by gel electrophoresis showed fragments in a ladder-like pattern typical of tandemly repetitive DNA. These fragments were cloned and their tandem organization in the genome was confirmed. A 51-bp long consensus sequence, which was AT-rich (59%) and contained a variable region and two imperfect reverse sequences, was obtained. Fluorescence in situ hybridization (FISH) localized this repetitive DNA into noncentromeric constitutive heterochromatin which encompasses the terminal region of some acrocentric chromosomes, the NOR region, and interstitial polymorphic heterochromatin in chromosome 24. Most remarkably, tandem repeats were almost symmetrically placed in the two arms of the B chromosome, with the exception of two additional small clusters proximally located on the slightly longer arm. Synaptonemal complex (SC) analysis showed 26 completely paired SCs in males with 1B. The ring configuration of the B univalent persisting until metaphase I suggests that the two arms formed chiasmata. All these data provided strong support for the hypothesis that the B chromosome is an isochromosome.

Accentuated polymorphism of heterochromatin and nucleolar organizer regions in Astyanax scabripinnis (Pisces, Characidae): tools for understanding karyotypic evolution

Astyanax scabripinnis has been considered a species complex because it presents high karyotypic and morphological variability among its populations. In this work, individuals of two A. scabripinnis populations from different streams in the same hydrographic basin were analyzed through C-banding and AgNOR. Although they present distinct diploid numbers, they show meta and submetacentric chromosome groups highly conserved (numerically and morphologically). Other chromosomal characteristics are also shared by both populations, as the pattern of constitutive heterochromatin distribution (large blocks in the telomeric regions of subtelocentric and acrocentric chromosomes) and some nucleolar chromosomes. Inter-individual variations both in the number and size of heterochromatic blocks, and in the number and localization of NORs were verified in the studied populations, characterizing them as polymorphics for these regions. The mechanisms involved in the dispersion of heterochromatin and NORs through the karyotypes, as well as the possible events related to the generation of polymorphism of those regions are discussed. Furthermore, relationships between these populations and within the context of the scabripinnis complex are also approached.

First report of a B chromosome in a natural population of Astyanax altiparanae (Characiformes, Characidae)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Chromosome polymorphism of heterochromatin and nucleolar regions in two populations of the fish Astyanax bockmanni (Teleostei: Characiformes)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Light microscopy and ultrastructure of the liver of Astyanax altiparanae Garutti and Britski, 2000 (Teleostei, Characidae).

Livers of thirty specimens of Astyanax altiparanae obtained from a commercial fish farm were subjected to light and transmission electron microscopy, in order to describe the hepatic parenchyma and the intrahepatic exocrine pancreatic tissue. Anatomically, the liver showed only three hepatic lobes. Histological analysis demonstrated that the hepatocytes were spread out as anastomotic cords, arranged in two cellular layers and surrounded by sinusoids. The intrahepatic exocrine pancreatic tissue exhibited an acinar arrangement and was diffused in the hepatic parenchyma. Ultrastructural analysis showed that the hepatocytes had a rounded nucleus and a rough endoplasmatic reticulum, with a parallel disposition to the nuclear membrane. The exocrine pancreatic cells showed secretion granules at the apical portion, and the rough endosplasmatic reticulum was concentrically distributed.

Cytogenetic characterization of a supernumerary chromosome segment and of B-chromosomes in Astyanax scabripinnis (Teleostei, Characidae)

The chromosome complement of a local population of Astyanax scabripinnis in Brazil was investigated with emphasis on the study of the heterochromatin attached to the A-chromosomes and present in the macro B-chromosome. Analysis after C-banding, silver and CMA(3) staining, incorporation of 5-bromo-2'-deoxyuridine and chromosome digestion with nine restriction endonucleases revealed that the heterochromatin in the B-chromosomes was different from that found in the A-chromosomes. A polymorphism due to the presence of a supernumerary heterochromatic chromosome segment was observed in the population investigated. Some aspects related to the origin of the heterochromatin polymorphism in Astyanax scabripinnis are discussed.