Apparent Plasticity Research Articles

Sexual maturity, fecundity, and embryo loss in the pontoniine shrimp Cuapetes americanus (Kingsley, 1878) (Decapoda: Palaemonidae) in Bahía de la Ascensión, Quintana Roo, Mexico

Cuapetes americanus (Kingsley, 1878) is distributed along the Atlantic coast of the Americas, from North Carolina and Bermuda to Sao Paulo, Brazil and the West Indies. The present goal was to conduct a comparative study of reproductive aspects of C. americanus: size at sexual maturity, fecundity, and embryo loss. Specimens were obtained from Bahia de la Ascension, Quintana Roo, Mexico in November 2000 (n=345) and November 2001 (n=156). Samples were collected with a marsh net on Thalassia testudinum-meadows. The average size of the specimens was significantly different between the two dates, with larger females in 2001 (2.46 ± 0.47 mm CL) than in 2000 (2.20 ± 0.23 mm CL). The size at which females reached sexual maturity was 2.01 ± 0.24 mm CL in 2000, and 2.39 ± 0.51 mm CL in 2001. The embryos were categorized in three embryonic stages. Average fecundity at the first stage of development was higher in specimens collected in 2001 (74 ± 57) than in 2000 (47 ± 21). On both sampling dates, fecundity increased with female size but also varied among females of the same size group. Embryos were significantly larger in 2000 than in 2001 (0.034 mm3 and 0.028 mm3, respectively). The maximum increase of embryo volume (78.5%) and brood loss (27.5%) with developmental stage was seen in 2001. The differences between the sampling dates and from others populations of this species from different localities suggested an apparent plasticity of the reproductive traits of C. americanus.

Brain gene expression patterns differentiate mild cognitive impairment from normal aged and Alzheimer's disease

Mild cognitive impairment (MCI) represents a cognitive state intermediate between normal aging and early Alzheimer's disease (AD). To investigate if the molecular signature of MCI parallels the clinical picture, we use microarrays to extensively profile gene expression in 4 cortical brain regions (entorhinal cortex, hippocampus, superior frontal gyrus, post-central gyrus) using the postmortem tissue from cognitively normal aged controls, MCI, and AD cases. Our data reveal that gene expression patterns in MCI are not an extension of aging, and for the most part, are not intermediate between aged controls and AD. Functional enrichment analysis of significant genes revealed prominent upregulation in MCI brains of genes associated with anabolic and biosynthetic pathways (notably transcription, protein biosynthesis, protein trafficking, and turnover) as well as mitochondrial energy generation. In addition, many synaptic genes showed altered expression in MCI, predominantly upregulation, including genes for central components of the vesicle fusion machinery at the synapse, synaptic vesicle trafficking, neurotransmitter receptors, and synaptic structure and stabilization. These data suggest that there is a rebalancing of synaptic transmission in the MCI brain. To investigate if synaptic gene expression levels in MCI were related to cognitive function, Pearson correlation coefficient between the Mini Mental State Examination (MMSE) and region-specific messenger RNA expression were computed for MCI cases. A number of synaptic genes showed strong significant correlations (r > 0.8, p < 0.01) most notably in the entorhinal cortex, with fewer in the hippocampus, and very few in neocortical regions. The synaptic genes with highly significant correlations were predominantly related to synaptic transmission and plasticity, and myelin composition. Unexpectedly, we found that gene expression changes that facilitate synaptic excitability and plasticity were overwhelmingly associated with poorer MMSE, and conversely that gene expression changes that inhibit plasticity were positively associated with MMSE. These data suggest that there are excessive excitability and apparent plasticity in limbic brain regions in MCI, that is associated with impaired synaptic and cognitive function. Such changes would be predicted to contribute to increased excitability, in turn leading to greater metabolic demand and ultimately progressive degeneration and AD, if not controlled.

Evolution of the Cytosolic Iron-Sulfur Cluster Assembly Machinery in Blastocystis Species and Other Microbial Eukaryotes

The cytosolic iron/sulfur cluster assembly (CIA) machinery is responsible for the assembly of cytosolic and nuclear iron/sulfur clusters, cofactors that are vital for all living cells. This machinery is uniquely found in eukaryotes and consists of at least eight proteins in opisthokont lineages, such as animals and fungi. We sought to identify and characterize homologues of the CIA system proteins in the anaerobic stramenopile parasite Blastocystis sp. strain NandII. We identified transcripts encoding six of the components-Cia1, Cia2, MMS19, Nbp35, Nar1, and a putative Tah18-and showed using immunofluorescence microscopy, immunoelectron microscopy, and subcellular fractionation that the last three of them localized to the cytoplasm of the cell. We then used comparative genomic and phylogenetic approaches to investigate the evolutionary history of these proteins. While most Blastocystis homologues branch with their eukaryotic counterparts, the putative Blastocystis Tah18 seems to have a separate evolutionary origin and therefore possibly a different function. Furthermore, our phylogenomic analyses revealed that all eight CIA components described in opisthokonts originated before the diversification of extant eukaryotic lineages and were likely already present in the last eukaryotic common ancestor (LECA). The Nbp35, Nar1 Cia1, and Cia2 proteins have been conserved during the subsequent evolutionary diversification of eukaryotes and are present in virtually all extant lineages, whereas the other CIA proteins have patchy phylogenetic distributions. Cia2 appears to be homologous to SufT, a component of the prokaryotic sulfur utilization factors (SUF) system, making this the first reported evolutionary link between the CIA and any other Fe/S biogenesis pathway. All of our results suggest that the CIA machinery is an ubiquitous biosynthetic pathway in eukaryotes, but its apparent plasticity in composition raises questions regarding how it functions in nonmodel organisms and how it interfaces with various iron/sulfur cluster systems (i.e., the iron/sulfur cluster, nitrogen fixation, and/or SUF system) found in eukaryotic cells.

Biomass allocation to vegetative and reproductive organs of Chenopodium acuminatum Willd. under soil nutrient and water stress

Biomass allocation was size-dependent. Under soil nutrient, the plasticity of the leaf and reproductive allocation was “true” plasticity, the plasticity of stem allocation was “apparent” plasticity, which is dependent on plant size, but there was no plasticity in root allocation. Under soil water stress, the plasticity of root, leaf and reproductive allocation was “true”. In response to population density, the plasticity of stem allocation is “true” plasticity, while the value of the stem allocation is consistent because of the trade off between the effects of plant size and population density. The biomass allocation strategy increases reproductive allocation but decrease leaf allocation with the decrease of soil nutrient, when compared at the same plant size. At lower soil water, the plant allocated more biomass to the root and leaf rather than to reproductive organ. DOI: http://dx.doi.org/10.3329/bjb.v42i1.15873 Bangladesh J. Bot. 42(1): 113-121, 2013 (June)

Effect of the addition of coal-ash and cassava peels on the engineering properties of compressed earth blocks

In developing countries, such as Colombia, earth construction is economically the most efficient means to solve housing problem with the least demand of resources. Traditional earth construction techniques such as compressed earth blocks are experiencing a new popularity, taking into account that they constitute green building materials becoming economically competitive. The availability everywhere of soils as raw materials, the low energy consumption and the simplicity of the production process justify their great usage as primary housing material in developing countries. A series of test compressed earth blocks were made using a clay-rich soil, without coal-ash and stabilized with coal-ash, in a Cinva-Ram hydraulic machine. The use of cassava peels as novel organic materials were also introduced in the preparation of the compressed earth blocks. The objective of this study is to investigate the effect of the addition of coal-ash and cassava peels on the engineering properties of compressed earth blocks. The samples were tested for flexion, compression and absorption in order to observe their performance. Results show that the compressive and bending tests reveal that the compressed earth blocks stabilized with coal-ash produced the best results using a dose less than or equal to 5%. However, doses greater than 5% generate more flexible and fragile compressed earth blocks. Adding cassava peels to the clayed soil increases the required water content for extrusion (apparent plasticity).

Positive mental health: A note of caution

Positive mental health: A note of caution

Regulatory T Cells Stay on Course

Regulatory T (Treg) cells are thought to be susceptible to conversion into effector T cells. In this issue of Immunity, Miyao et al. (2012) provide evidence that the apparent plasticity of murine Foxp3(+) Treg cells is largely restricted to a defined subset of poorly committed Foxp3(+) cells.

In Vitro Generation of Pancreatic Endocrine Cells from Human Adult Fibroblast-Like Limbal Stem Cells

Stem cells might provide unlimited supply of transplantable cells for β-cell replacement therapy in diabetes. The human limbus is a highly specialized region hosting a well-recognized population of epithelial stem cells, which sustain the continuous renewal of the cornea, and the recently identified stromal fibroblast-like stem cells (f-LSCs), with apparent broader plasticity. However, the lack of specific molecular markers for the identification of the multipotent limbal subpopulation has so far limited the investigation of their differentiation potential. In this study we show that the human limbus contains uncommitted cells that could be potentially harnessed for the treatment of diabetes. Fourteen limbal biopsies were obtained from patients undergoing surgery for ocular diseases not involving the conjunctiva or corneal surface. We identified a subpopulation of f-LSCs characterized by robust proliferative capacity, expressing several pluripotent stem cell markers and exhibiting self-renewal ability. We then demonstrated the potential of f-LSCs to differentiate in vitro into functional insulin-secreting cells by developing a four-step differentiation protocol that efficiently directed f-LSCs towards the pancreatic endocrine cell fate. The expression of specific endodermal, pancreatic, islet, and β-cell markers, as well as functional properties of f-LSC-derived insulin-producing cells, were evaluated during differentiation. With our stage-specific approach, up to 77% of f-LSCs eventually differentiated into cells expressing insulin (also assessed as C-peptide) and exhibited phenotypic features of mature β-cells, such as expression of critical transcription factors and presence of secretory granules. Although insulin content was about 160-fold lower than what observed in adult islets, differentiated cells processed ∼98% of their proinsulin content, similar to mature β-cells. Moreover, they responded in vitro in a regulated manner to multiple secretory stimuli, including glucose. In conclusion, f-LSCs represent a possible relevant source of autologous, transplantable, insulin-producing cells that could be tested for the reversal of diabetes.

Assessing attraction or avoidance between rabbits: comparison of distance-based methods to analyse spatial distribution

Studies on social spacing usually analyse spatial distribution using a single distribution index, and compare this with expected values assuming random spacing. However, different distribution indices give information on different aspects of spatial distribution. Furthermore, when animals use some parts of the study area more often because of environmental factors, assumptions of random spacing do not apply. As a contribution to the development of spatial distribution analysis methodology, we compared three distribution indices: nearest-neighbour distances (NND), coefficient of variation of interindividual distances and coefficient of variation of Dirichlet polygon areas. Distribution was studied at different animal densities, in the presence or absence of a wooden structure. Rabbits, Oryctolagus cuniculus, were chosen as the model species because of their apparent plasticity of spatial behaviour. The observed distribution was compared with a random distribution and with a resource-corrected random distribution that accounted for environmental influences on spacing. Comparisons with these two distributions led to different conclusions. This emphasizes the limited usefulness of comparisons with the random distribution, especially in more heterogeneous environments. However, divergence from random spacing could potentially be used to assess the relative importance of resources. Especially for 6-week-old rabbits, the density at which no evidence of avoidance was found differed between the distribution indices. This underlines the need to use multiple indices when studying social spacing. Nine-week-old rabbits generally avoided each other’s proximity, with NND indicating proximity avoidance even in the largest pens. Contrary to expectations, the wooden structure seemed to decrease social attraction between rabbits.

Evolution of the T cell receptor: expression of non-conventional TCRδ chains in Xenopus (170.7)

Abstract γδ T cell receptors (TCR) that have structural differences from conventional γδ T cells in mammals have been observed in non-eutherian vertebrates. Three different types of V regions are present in the frog Xenopus tropicalis genomic TCRδ locus (Eur. J. Immunol. 40: 2319, 2010), most similar to Vδ, Vα, and VHδ (evolutionarily derived from the V regions of Ig H chains). We have begun a survey of the tissue distribution of TCRδ expression in X. laevis tadpoles and adults by 5’ RACE PCR. The deduced amino acid sequences predicted from X. tropicalis genome sequences were aligned with those from X. laevis TCRδ V RACE clones, revealing similar Vδ, Vα, and VHδ families in X. laevis. Analyses of the TCRδ RACE nucleotide sequences have identified the putative D and J gene segments in X. laevis as well. Although we find representatives of all TCRδ V sub-families in all tested adult tissues, the distribution of the data suggests that the expressed repertoire is skewed in some tissues, especially in the skin, where a majority of recovered sequences were of the Vα type. Interestingly, analyses of the Vδ type indicate a lack of N-nucleotide addition in the CDR3 in adults, suggestive of a population of T cells that is generated during larval life that persists through metamorphosis. Continued study of these unique TCR in Xenopus will illuminate apparent plasticity in TCR evolution, and shed light on how γδ TCR recognize antigen in all vertebrates.

Aspectos ecológicos de stenocercus caducus (squamata:iguanidae) en fragmentos boscosos en el suroeste de mato grosso, brasil

Stenocercus caducus es un Tropidurinae descrito para Paraguay, Brasil (Mato Grosso e Pará) Bolivia (Beni, Chuquisaca, Cochabamba, La Paz, Santa Cruz, Tarija) y Argentina (Jujuy, Salta). Aparentemente es poco exigente en cuanto al hábitat, ya que es encontrado en áreas de cerrados, cerradones, matas ciliares y eventualmente en áreas antropizadas. En este estudio se presentan aspectos ecológicos de S. caducus, muestreados en 18 fragmentos insertados en una matriz de pradera, en la región sudeste de Mato Grosso en un área de la Floresta Estacional Semidecidua Submontana. Se realizaron las colectas en período seco y lluvioso entre diciembre de 2002 y agosto de 2004, a través de trampas tipo pitfall, con esfuerzo muestreal de 9.000 baldes/día. Fue determinada la estructura poblacional, observando la ocurrencia de solo adultos en el período lluvioso y predominancia de jóvenes en el período seco. La relación sexual encontrada estuvo próxima a 1:1 en ambos períodos, no siendo encontrada diferencias significativas en los patrones morfométricos entre los sexos. En cuanto al uso de hábitat, la especie se mostró generalista, utilizando tanto la matriz de pastos o pradera, orilla e interior de los fragmentos, aparentando preferencia por la orilla. En relación con la dieta, estaba exclusivamente compuesta por artrópodos, detectándose una ingestión que incluye un amplio espectro de presas, siendo más frecuentes y numerosas los insectos de los órdenes Coleóptera, Himenóptera (Formicidae) e Isóptera. La aparente plasticidad de la especie en cuanto al uso de hábitat y dieta contribuye para que sea exitosa, ya que una vez que se amplía el territorio de forrajeo aumenta la capacidad de sobrevivencia, siendo favorecida por la transformación de las áreas de Cerrado en un mosaico de fragmentos, debido a los constantes impactos antrópicos que suceden.

Adult pancreatic acinar cells give rise to ducts but not endocrine cells in response to growth factor signaling.

Studies in both humans and rodents have found that insulin(+) cells appear within or near ducts of the adult pancreas, particularly following damage or disease, suggesting that these insulin(+) cells arise de novo from ductal epithelium. We have found that insulin(+) cells are continuous with duct cells in the epithelium that makes up the hyperplastic ducts of both chronic pancreatitis and pancreatic cancer in humans. Therefore, we tested the hypothesis that both hyperplastic ductal cells and their associated insulin(+) cells arise from the same cell of origin. Using a mouse model that develops insulin(+) cell-containing hyperplastic ducts in response to the growth factor TGFalpha, we performed genetic lineage tracing experiments to determine which cells gave rise to both hyperplastic ductal cells and duct-associated insulin(+) cells. We found that hyperplastic ductal cells arose largely from acinar cells that changed their cell fate, or transdifferentiated, into ductal cells. However, insulin(+) cells adjacent to acinar-derived ductal cells arose from pre-existing insulin(+) cells, suggesting that islet endocrine cells can intercalate into hyperplastic ducts as they develop. We conclude that apparent pancreatic plasticity can result both from the ability of acinar cells to change fate and of endocrine cells to reorganize in association with duct structures.

Effects of hydrology on the growth and physiology of an invasive exotic, Lygodium microphyllum (Old World climbing fern)

SummaryWe conducted a glasshouse study to examine effects of hydrology on the growth and physiology of Lygodium microphyllum (Old World climbing fern), an invasive exotic that is rapidly colonising forested wetlands in Florida, USA. We assessed the fern’s growth and physiological responses to three hydrological treatments – flood, drought and field capacity. To further explore the physiology of the treatment responses of L. microphyllum, we also sprayed each plant with gibberellic acid, paclobutrazol (gibberellin inhibitor) or a water control solution (at a rate of 5 mL three times per week) using a 3 × 3 factorial design. Flooding reduced relative growth rate by 55%, whereas periodic exposure of ferns to a soil water potential of −1 MPa did not affect growth or physiology. Flooding led to substantial decreases in specific leaf area and area‐based rates of pinna photosynthesis, resulting in a 64% lower rate of photosynthesis per unit pinna mass. Application of growth regulators had no effect on fern growth, morphology or physiology. Even though flooding substantially reduced growth, L. microphyllum still showed a positive relative growth rate after &gt;2 months of inundated soils. This apparent hydrological plasticity is likely a contributing factor to the introduced fern’s widespread establishment across a range of plant communities within the Florida Everglades ecosystem. Short‐term manipulation of site hydrology does not appear to be an effective management option. Consequently, this has considerable implications for the Everglades, which is undergoing a 30‐year system‐wide hydrological restoration.

Is reproductive allocation inSenecio vulgarisplastic?

Several purported cases of plasticity in plant allocation patterns appear to be the effects of size and allometric growth (“apparent plasticity”). To ask whether there is true plasticity (i.e., a change in the allometric trajectory) in reproductive allocation in Senecio vulgaris L., we grew S. vulgaris plants at high and low levels of water, nutrients, and competition, and analyzed the relationship between vegetative and seed biomass. Plant size was the major determinant of reproductive output, accounting for 83% of the variation in log (seed mass). There were also significant effects of the treatments that were not due to size, accounting for an additional 9% of the variation. The treatments affected the allometric coefficient (intercept), not the allometric exponent (slope) of the relationship, reflecting a small but significant shift in the efficiency of conversion of total plant biomass into reproductive biomass. In a second experiment, we grew S. vulgaris plants at three nutrient levels and allowed all individuals to complete their life cycles. Again, nutrient level had a small but significant effect on the allometric coefficient. Plasticity in reproductive allocation exists, but is very limited. The primary effects of the environment on the reproductive output of S. vulgaris occur via plant size.

CD27 is a thymic determinant of the balance between interferon-γ- and interleukin 17–producing γδ T cell subsets

The production of cytokines such as interferon-gamma and interleukin 17 by alphabeta and gammadelta T cells influences the outcome of immune responses. Here we show that most gammadelta T lymphocytes expressed the tumor necrosis factor receptor family member CD27 and secreted interferon-gamma, whereas interleukin 17 production was restricted to CD27(-) gammadelta T cells. In contrast to the apparent plasticity of alphabeta T cells, the cytokine profiles of these distinct gammadelta T cell subsets were essentially stable, even during infection. These phenotypes were established during thymic development, when CD27 functions as a regulator of the differentiation of gammadelta T cells at least in part by inducing expression of the lymphotoxin-beta receptor and genes associated with trans-conditioning and interferon-gamma production. Thus, the cytokine profiles of peripheral gammadelta T cells are predetermined mainly by a mechanism involving CD27.

Plasticity and allometry of meristem allocation in response to density in three annual plants with different architectures

An experiment was conducted to investigate plasticity of meristem allocation under intraspecific competition in three annual species ( Xanthium sibiricum Patrin., Datura stramonium L., and Fagopyrum esculentum Moench.) with different architectures (monopodial, false dichotomous, and sympodial branching, respectively). There were two density treatments for X. sibiricum and D. stramonium, with plant–plant distances of 7 and 14 cm, and five density treatments for F. esculentum, with plant–plant distances of 5, 10, 15, 20, and 25 cm. We recorded meristem fates (inactive, growth, and reproduction) at several developmental stages and at the final developmental stage. Allocation of meristems to reproduction in all three species could be explained by allometric growth (“apparent plasticity”), but meristem allocation patterns to the other functions differed among the species. Allocation of meristems to growth affects and is affected by plant architecture. Our results suggest that vegetative growth is more plastic than reproduction in annual plants.

Embryonic Stem Cells Contribute to Mouse Chimeras in the Absence of Detectable Cell Fusion

Embryonic stem (ES) cells are capable of differentiating into all embryonic and adult cell types following mouse chimera production. Although injection of diploid ES cells into tetraploid blastocysts suggests that tetraploid cells have a selective disadvantage in the developing embryo, tetraploid hybrid cells, formed by cell fusion between ES cells and somatic cells, have been reported to contribute to mouse chimeras. In addition, other examples of apparent stem cell plasticity have recently been shown to be the result of cell fusion. Here we investigate whether ES cells contribute to mouse chimeras through a cell fusion mechanism. Fluorescence in situ hybridization (FISH) analysis for X and Y chromosomes was performed on dissociated tissues from embryonic, neonatal, and adult wild-type, and chimeric mice to follow the ploidy distributions of cells from various tissues. FISH analysis showed that the ploidy distributions in dissociated tissues, notably the tetraploid cell number, did not differ between chimeric and wild-type tissues. To address the possibility that early cell fusion events are hidden by subsequent reductive divisions or other changes in cell ploidy, we injected Z/EG (lacZ/EGFP) ES cells into ACTB-cre blastocysts. Recombination can only occur as the result of cell fusion, and the recombined allele should persist through any subsequent changes in cell ploidy. We did not detect evidence of fusion in embryonic chimeras either by direct fluorescence microscopy for GFP or by PCR amplification of the recombined Z/EG locus on genomic DNA from ACTB-cre::Z/EG chimeric embryos. Our results argue strongly against cell fusion as a mechanism by which ES cells contribute to chimeras.

Nestin-positive spheres derived from canine bone marrow stromal cells generate cells with early neuronal and glial phenotypic characteristics

Bone marrow stromal cells (BMSCs) isolated from humans and rodents have been shown to generate neural cells under specific culture conditions and after transplantation in the central nervous system. The apparent plasticity of BMSCs has therefore been a target of intensive research in attempt to develop a novel therapy for neurological diseases. Canines sustain neurological disorders (e.g., traumatic spinal cord injury) that closely mirror pathology of those in humans. Therefore, we evaluated neural differentiation properties of canine BMSCs to provide insights into basic characterization of these cells for future neurotransplantation trials in canine patients with neurological disorders. We demonstrate that canine BMSCs form spherical cellular aggregates on anti-adhesive culture substrate in serum-free culture media, which morphologically and phenotypically resemble spherical aggregates of neural progenitor cells, so-called neurospheres. Upon dissociation and subculture on adhesive substrate, canine BMSCs express neuronal (ss capital SHA, Cyrillic-tubulin) and glial (GFAP, A2B5, and CNPase) markers. Formation of spherical aggregates appears to be a critical preceding process for some of the glial marker expression (CNPase and A2B5). However, expression of more mature neuronal (MAP2) and glial (MBP) markers could not be induced with the protocol used in this study. We suggest that induction of canine BMSCs into cells with neural progenitor cell characteristics is possible and that these cells may have the potential for future cellular therapy for neurological disorders.

Poisson’s ratio and fragility of bulk metallic glasses

The correlation among apparent global plasticity, Poisson’s ratio, and fragility in monolithic bulk metallic glass (BMG) alloys has been investigated in the present study. The shear and bulk moduli in monolithic Cu-based BMG alloys have been measured by resonant ultrasound spectroscopy (RUS) and ultrasonic technique. The Cu43Zr43Al7Ag7 BMG alloy showing a large apparent global plasticity (∼8%) exhibits a high Poisson’s ratio when compared with that of Cu43Zr43Al7Be7 BMG alloy. In addition, the fragility of Cu-based BMG alloys can be obtained by differential scanning calorimetry (DSC). The fragility index m of Cu43Zr43Al7Ag7 BMG alloy is slightly larger than that of Cu43Zr43Al7Be7 BMG alloy. The correlation between Poisson’s ratio and fragility in BMG alloys can be presented by a simple relation of m − 17 = 14 (B∞/G∞ − 1). Poisson’s ratio and fragility might be regarded as an important parameter that controls global plasticity of glass-forming alloys.

Cytogenetic and morphological diversity in populations of Astyanax fasciatus (Teleostei, Characidae) from Brazilian northeastern river basins

In the present work, morphometric and cytogenetic analyses were carried out in populations of the fish Astyanax fasciatus (Characidae) from Contas and Recôncavo Sul River basins (State of Bahia, Brazil), providing new data on the genetic structure of this species along the region. Based on morphologic measurements, we observed that populations from the same hydrographic basin were more similar to each other (Contas and Preto do Costa Rivers), and remarkably divergent from Recôncavo Sul (Mineiro Stream), as indicated by clustering analysis. Cytogenetic data revealed a same diploid number for all populations (2n = 48), but distinct karyotype formulae (8M+24SM+12ST+4A, FN = 92 in Contas River, 8M+24SM+10ST+6A, FN = 90 in Preto do Costa River, and 8M+18SM+16ST+6A, FN = 90 in Mineiro Stream). Ag-NORs were identified at telomeres on a subtelocentric chromosome pair, although multiple ribosomal sites have been detected in some specimens from Contas River. These results show that A. fasciatus populations from northeastern river basins are well differentiated and present peculiar cytogenetic features when compared to populations from other regions. Therefore, the apparent chromosomal plasticity of this species, likely to represent a complex of cryptic forms, is corroborated. Finally, we demonstrated that morphological features can be successfully used to support other sources of genetic information.