Occurrence of macro B chromosomes in Astyanax scabripinnis paranae (Pisces,Characiformes, Characidae)

B chromosomes occur in several Neotropical fish species. Cytogenetic analysis of 27 specimens (15 females and 12 males) of Astyanax scabripinnis paranae from the Araquá river (a small headwater tributary of the Tietê river) shows that this population has 2n=50 chromosomes (4M+30 SM+4ST+12A), two chromosome pairs with NORs and conspicuous C-band positive blocks in the terminal position of the long arm of four chromosome pairs. In this population, eight females presented 2n=51 chromosomes and the extra chromosome was a large metacentric similar in size and morphology to the first chromosome pair in the karotype. This accessory chromosome is entirely heterochromatic in C-banded metaphases and shows a late replication pattern evidenced by BrdU incorporation. There was no significant correlation between the presence of B chromosomes and increased NOR activity at the P>0.05 level. Some aspects related to these B chromosomes are discussed.     

Population Genetic Structure of Astyanax scabripinnis (Teleostei, Characidae) from an Urban Stream

Despite the great anthropogenic interference on urban streams, information is still scarce about the genetic variability and structure of native fish populations inhabiting such streams. In the present study, random amplified polymorphic DNA (RAPD) markers were used to analyze genetic variability and structure of populations assigned to the Neotropical fish species Astyanax scabripinnis from an urban stream located in Londrina, Paraná State, southern Brazil. Thirty individuals of this species were collected from three sites throughout the upper Cambé stream. A total of 10 primers amplified 159 loci, of which 128 (80.5%) were polymorphic. Each of the three populations showed very similar proportions of polymorphic loci, which ranged from 63.5 to 64.8%. Unbiased genetic distances varied from 0.0612 to 0.0646. Theta_p-test values indicated moderate to high genetic differentiation among individuals from different localities. The number of migrants varied from 1.34 to 1.46, suggesting a low gene flow between populations. The genetic similarity among all individuals studied ranged from 0.424 to 0.848. The results suggest that populations of A. scabripinnis in Cambé stream are undergoing genetic differentiation.     

Reproduction of the lambari Astyanax scabripinnis (Jenyns, 1842) (Pisces: Characidae) in a small stream in Southeastern Brazil

The reproduction of Astyanax scabripinnis captured bimonthly in the Cristais small stream (20^o00'03'S and 43^o56'46'W), in the Das Velhas River basin, was studied using gross anatomical and histological techniques. Standard length of females (56 ± 8 mm) was longer than males (49 ± 6 mm). The diameter of the nucleus of the primary spermatogonia was 7.5 ± 0.9  μ m and of the spermatozoon head 1.8 ± 0.4  μ m. For the females, the oogonia nuclei measured 10.2 ± 2.2  μ m and the vitellogenic oocyte nuclei measured 675.0 ± 66.7  μ m. The following stages of the reproductive cycle were established: developing, mature, partially spent/spawned and completely spent/spawned. Maximum number of males (61.3%) and females (58.2%) at the mature stage was observed during November/December. The gonadosomatic index of males and females was highest during the mature stage (2.4 ± 0.6; 7.5 ± 1.3, respectively) and decreased in subsequent stages. In females, the hepatosomatic index was highest during the developing stage (2.8 ± 0.3), and slightly decreased in the following stages. The highest stomach repletion index found for males was observed during the partially spent stage (2.0 ± 1.2), while for the females, this index varied discretely between the reproductive stages. The highest values of Fulton's condition factor were registered during the mature stage in both sexes (2.9 ± 0.4 for males; 3.0 ± 0.3 for females). The continuous reproductive period and the presence of partially spawned females during the entire sampling period indicated that the species has fractional spawning.     

B Chromosome Polymorphism in the Fish, Astyanax scabripinnis

Four populations of Astyanax scabripinnis (Pisces, Characidae) were analyzed for B chromosome features. This species contains a metacentric macrochromosome (B_M), similar in size to the first chromosome of the karyotype, besides two variant forms, a large submetacentric (B_SM) and a small metacentric (B_m), both showing a reduced frequency. These variant forms were observed only in the populations from the Campos do Jordão region (São Paulo State, Brazil), although not present in all the populations sampled. The three B chromosome forms are heterochromatic and at least the B_M and B_SM are also GC-rich, as evidenced by C-banding and chromomycin A₃ staining. In spite of the morphological similarity between the B_M form and the first chromosome pair, they differ in the G-banding pattern, which does not favor a possible relationship among these chromosomes. FISH with a telomeric DNA probe evidenced signals on the terminal region of all chromosomes, including the Bs. Interstitial telomeric bands, indicative of some chromosomal rearrangements such as translocation or tandem fusion in the origin of the B chromosomes, were not observed. B_SM and B_m are probable derivative B chromosome forms from an ancestral B_M chromosome, showing a restricted occurrence and low frequency in the populations.     

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 CMA₃ 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. This revised version was published online in July 2006 with corrections to the Cover Date.     

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. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparative cytogenetics among populations of Astyanax altiparanae (Characiformes, Characidae, Incertae sedis)

Cytogenetic data are presented for Astyanax altiparanae populations from three Brazilian hydrographic systems. The chromosomal data obtained in A. altiparanae support the hypothesis of diploid number conservation. However, small differences in the karyotype formula and number of nucleolar organizer regions were observed in these populations. The apparent karyotypical similarity among the studied populations strongly suggests a close relationship among them with some chromosomal divergences due to gene flow restriction.     

Genetic divergence between cave and surface populations of Astyanax in Mexico (Characidae,Teleostei)

A study of genetic diversity at microsatellite loci and the mitochondrial DNA (mtDNA) cytochrome b gene was carried out to assess genetic relationships among four Mexican cave (Pachon, Sabinos, Tinaja, Chica) and four surface populations of Astyanax fasciatus (Characidae) from northeast Mexico and the Yucatan. With the exception of Chica, the cave populations were all characterized by extremely low microsatellite variability, which most likely resulted from bottleneck events. Population analyses of the microsatellite data indicated no measurable levels of gene flow between all cave and surface populations (F(ST) > 0.0707). Phylogenetic analyses of mtDNA data showed that only two cave populations - Sabinos and Tinaja - group together to the exclusion of surface populations. From the microsatellite data these cave populations cluster with the Pachon cave fish population. The mtDNA thus appears to have been replaced in Pachon because of introgressive hybridization. It is likely that these three cave populations have descended from a surface ancestor in common with current surface populations, rather than evolving recently from one of the extant surface populations. Like Pachon, the Chica population clustered with the surface populations according to mtDNA data, but was not clearly associated with either the surface or the other cave populations according to the microsatellite data. Our data indicate that the Chica population evolved recently from a surface population, and subsequently hybridized with a phylogenetically older cave population. In conclusion, both the microsatellite and mtDNA data suggest multiple origins of cave populations and the Chica and Sabinos/Tinaja/Pachon were founded after at least two independent invasions from surface populations.     

Multiple Nors in Bryconamericus aff. exodon (Osteichthyes,Characidae, Tetragonopterinae)

Fifteen examples of Bryconamericus aff. exodon from the Três Bocas stream in the basin of the Tibagi river (Parana, Brazil) were analyzed. They presented a diploid number of 52 chromosomes. Multiple NORS were detected by silver nitrate impregnation in the telomeric region on the short or long arm of different chromosomes, showing a variation from 2 to 5 NOR-bearing chromosomes. Treatment with chromomycin A3 (CMA3) showed regions rich in GC in different chromosomes, probably coincident with the AgNORS. In situ hybridization by fluorescence (FISH) with 18S rDNA probe showed 8 hybridization signs in the telomeric regions of the chromosomes, proving that this B. aff. exodon population has a greater number of ribosomal cistrons than were detected by Ag-banding.     

Oxygen consumption of Astyanax fasciatus (Characidae,Pisces): a comparison of epigean and hypogean populations

Synopsis The standard and routine oxygen consumptions of Astyanax fasciatus from one surface population (Rio Teapao) and three cave populations (Chica, Micos and Pachon caves: sAnoptichthys jordani, the Micosfish and Anoptichthys antrobius) were determined individually over 24 hours by the use of a flow-through respirometer and polarographic oxygen electrodes. The phylogenetically oldest Pachon fish had a significantly lower standard metabolic rate (0.230 ± 0.036 mg O₂ g^-1 h^-1) than the epigean Teapao fish, the hybrid Chica fish and the phylogenetically younger Micos fish (0.314 ± 0.081 mg O₂g-^-1h^-1, 0.284 ± 0.048 mg O₂g^-1h^-1, 0.277 ± 0.063 mg O₂g^-1h^-1). No significant differences could be determined among the latter three populations. A significant difference in routine metabolic rate existed only between the Pachon fish (0.309 ± 0.0.56 mg O₂g^-1h^-1) and the Teapao fish (0.415 ± 0.071 mg O₂g^-1h^-1). The Chica fish (0.356 ± 0.084 mg O₂g^-1h^-1) and the Micos fish (0.355 ± 0.080 mg O₂ g^-1h^-1) could not be separated from either the Teapao or the Pachon fish, but a decreasing trend from the surface population through the Chica and the Micos to the Pachon population was obvious. During a starvation period of 29 days the metabolic rate of epigean Teapao and hypogean Pachon fish decreased significantly by 32.5% and 34.8% (standard oxygen consumption rate) and 27.5% and 28.2% (routine oxygen consumption rate), respectively. Body mass loss during the starvation period was 16.3% for the Teapao fish and 9.5% for the Pachon fish.     

NADP-dependent isocitrate dehydrogenase of Astyanax scabripinnis (Pisces, Characidae) from three altitudes at Grande Stream, Campos do Jord?o, SP.

Electrokinetic, thermic, and kinetic properties of products of NADP-dependent isocitrate dehydrogenase (IDHP; EC 1.1.1.42) loci of Astyanax scabripinnis (Pisces, Characidae) collected at three different altitudes (700 m, 1,800 m, and 1,920 m) of Grande Stream at Campos do Jord?o, State of S?o Paulo, Brazil, were analyzed. Two IDHP bidirectionally divergent loci, a single skeletal muscle, the IDHP-A*, and a single liver IDHP-B*, both polymorphic, were detected in the three different altitude populations. The variant allele *128 at the IDHP-A* locus, had its highest frequency detected in the 1,920 m population (0.494). Among the nine variant alleles detected at the IDHP-B* locus (*37, *57, *69, *79, *85, *114, *119, *124, and *140), the *37 and 79 were detected only in 1,800 m population. Chi-square values showed that only the 700 m population is not in Hardy-Weinberg equilibrium for the IDHP-A* locus, while for the IDHP-B* locus, no population is. Homogeneity Chi2 test indicated that the populations are significantly different in their A and B phenotype frequencies. Wright's FST mean value (0.036 and 0.32, IDHP-A* and IDHP-B*, respectively) was 0.178 for the three altitude populations which means that 82% of total genetic diversity was found among individuals of each one of the populations. Stability at environmental temperatures (16 degrees to 21 degrees C), and apparent Km and Vmax values of each A-phenotype skeletal muscle crude extract suggest different roles of A-isoforms during the increased lipogenesis that occurs in fish at low temperatures.     

Larval feeding behaviour of blind fish Astyanax fasciatus (Characidae), black tetra Gymnocorymbus ternetzi (Characidae) and angel fish Pterophyllum scalare (Cichlidae) fed zooplankton

We studied the feeding behaviour during the larval stages (from hatching until 8 weeks) of the Mexican blind fish Astyanax fasciatus, black tetra Gymnocorymbus ternetzi and angel fish Pterophyllum scalare using four zooplankton species (two rotifers: Brachionus calyciflorus and B. patulus and two cladocerans: Daphnia pulex and Moina macrocopa). Components of feeding behaviour (numbers of encounters, attacks, captures, ingestions, rejections and escapes) were quantified for 10 min observation periods per larvae. Data on the increase of the body length and mouth size of the three fish species during this period were also collected. When B. calyciflorus was used as prey, P. scalare showed higher capture and ingestion rates than A. fasciatus or G. ternetzi. With reference to age, B. calyciflorus was more frequently attacked, captured and ingested by G. ternetzi and P. scalare than A. fasciatus from the first to the 8th week. When offered B. patulus as prey, larvae of the three fish species showed increased consumption of B. patulus with time. A. fasciatus sometimes rejected B. patulus which could also escape after being captured. A. fasciatus began to attack and ingest Daphnia pulex and Moina macrocopa from the first week onwards while, G. ternetzi could neither capture nor ingest cladocerans until the fifth week. P. scalare began to ingest M. macrocopa and D. pulex from the third week onwards. These results are discussed with reference to the non-functional eyes of larval A. fasciatus.     

Feeding ecology of three Astyanax species (Characidae, Tetragonopterinae) from a floodplain lake of Mogi-Guaçú River, Paraná River Basin, Brazil

Synopsis The feeding ecology of three characids (A. fasciatus, A. bimaculatus and A. schubarti) was studied monthly during 1988 in Lake Inferñao, a major floodplain lake of the Mogi-Guaçú River in the State of São Paulo. River flooding directly influenced the diet of the omnivorous A. bimaculatus and A. fasciatus which responded to maximum inundation (March) by consuming predominantly allochthonous insects. In contrast, A. schubarti was less influenced by the river flood cycle on qualitative changes in diet and relied basically on aquatic macrophytes and periphytic algae. The importance of zooplankton in the diet of the three species was low, and may be attributed to its low density in the water column (< 1 ind l^–1). Ontogenetic diet changes were evident for the three species. For A. fasciatus and A. bimaculatus the importance of zooplankton was high at the early stages, decreasing with size. A. schubarti at younger stages consumed diversified items which gradually decreased quantitatively up to the size class of 65 mm; from this size onwards, the diet became restricted to the consumption of periphytic algae and macrophytes.     

Aggressive behaviour of an epigean population of Astyanax mexicanus (Characidae,Pisces) and some observations of three subterranean populations

The different populations have been tested for aggressive behaviour in groups of four to eight animals of both sexes in tanks ranging from 251 to 9501. In darkness less aggressive behaviour has been observed with the help of an infrared video-camera in the epigean fish and the eyed Micos cave fish. The strongest degree of reduction in aggressive behaviour is shown by the totally blind populations. The aggressiveness increases in the epigean fish as soon as space and food supply diminish.     

Gonadal morphology and difference in reproductive development of two isolated populations of Astyanax rivularis (Teleostei,Characidae)

Individuals of the same species may present different reproductive tactics depending on the environment in which they develop and mature. The present study aimed to define the gonadal development phases of males and females of Astyanax rivularis and to carry out a comparative analysis of the reproductive development of specimens captured in two isolated environments of the São Francisco River basin in Serra da Canastra, Brazil (Point 1: low vegetation and river showing calm and crystalline waters with small well formations; Point 2: current waters, and well-established areas of arboreal vegetation). Thus, the gonads of A. rivularis specimens were collected, fixed and processed with techniques for light microscopy. Five maturation phases of the females' reproductive cycle were established: immature, developing, spawning capable, regressing and regenerating. Three maturation phases of the males' reproductive cycle were observed: spawning capable, regressing, and regenerating. There are differences in the phases of gonadal development of A. rivularis between the two sampling points so that, possibly, animals upstream of the waterfall demonstrate a delay in the reproductive cycle in relation to animals downstream.     

Ontogenetic transition from unicuspid to multicuspid oral dentition in a teleost fish: Astyanax mexicanus, the Mexican tetra (Ostariophysi: Characidae)

Teleost fishes display a remarkable diversity of adult dentitions; this diversity is all the more remarkable in light of the uniformity of first-generation dentitions. Few studies have quantitatively documented the transition between generalized first-generation dentitions and specialized adult dentitions in teleosts. We investigated this transition in the Mexican tetra, Astyanax mexicanus (Characidae), by measuring aspects of the dentition in an ontogenetic series of individuals from embryos to 160 days old, in addition to adults of unknown age. The first-generation dentition and its immediate successors consist of small, unicuspid teeth that develop extraosseously. Multicuspid teeth first appear during the second tooth replacement event, and are derived from single tooth germs, rather than from the fusion of multiple conical tooth germs. We document that the transition from unicuspid to multicuspid teeth corresponds to a change in the location of developing tooth germs (from extraosseous to intraosseous) and in patterns of tooth replacement (from haphazard to simultaneous within a jaw quadrant). In addition, while the size of the largest teeth scales with positive allometry to fish size, the transition to multicuspid teeth is accompanied by an exceptionally large increase in tooth size.  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 145 , 523–538.