Anthropogenic impact of mercury accumulation in fish from the Rio Madeira and Rio Negro rivers (Amazonia)

Fish is an important concentrator of mono-methyl mercury and the main route to human contamination. We compared fish Hg bioaccumulation (within similar weight ranges) in two Amazonian river habitats during high-water seasons. The Rio Madeira has been greatly impacted by agriculture, alluvial gold extraction, and a hydroelectric reservoir, whereas the Rio Negro is much less affected by these human activities. The species at the top of the food web, Hoplias malabaricus (piscivorous; 80-668 ng Hg/g) and Cichla spp. (piscivorous; 42–747 ng Hg/g) showed the highest range of Hg concentrations. Nonpiscivorous species with comparable weight range, such as Potamorhina latior (detritivorous; 20–157 ng Hg/g) and Myleus torquatus (herbivorous; 2–182 ng Hg/g), had lower Hg concentrations. Triportheus elongatus (omnivorous; 5–350 ng Hg/g), with the lowest weight range, also showed a low range of Hg concentrations. Despite the Rio Madeira's higher sediment load as well as environmental impacts (deforestation, agriculture, hydroelectric reservoir, and alluvial gold mining) on natural Hg release, fish Hg bioaccumulation was no different between the two river habitats for nonpiscivorous species. In this small observational study only the species at the top of the food web (M. torquatus, Cichla spp, T. elongatus) showed higher mean Hg concentrations in the Rio Madeira than the dominantly wilderness habitat of the Rio Negro.     

Diverse strategies for ion regulation in fish collected from the ion-poor, acidic Rio Negro

We measured unidirectional ion fluxes of fish collected directly from the Rio Negro, an extremely dilute, acidic blackwater tributary of the Amazon. Kinetic analysis of Na(+) uptake revealed that most species had fairly similar J(max) values, ranging from 1,150 to 1,750 nmol g(-1) h(-1), while K(m) values varied to a greater extent. Three species had K(m) values <33 micromol L(-1), while the rest had K(m) values >or=110 micromol L(-1). Because of the extremely low Na(+) concentration of Rio Negro water, the differences in K(m) values yield very different rates of Na(+) uptake. However, regardless of the rate of Na(+) uptake, measurements of Na(+) efflux show that Na(+) balance was maintained at very low Na(+) levels (<50 micromol L(-1)) by most species. Unlike other species with high K(m) values, the catfish Corydoras julii maintained high rates of Na(+) uptake in dilute waters by having a J(max) value at least 100% higher than the other species. Corydoras julii also demonstrated the ability to modulate kinetic parameters in response to changes in water chemistry. After 2 wk in 2 mmol L(-1) NaCl, J(max) fell >50%, and K(m) dropped about 70%. The unusual acclimatory drop in K(m) may represent a mechanism to ensure high rates of Na(+) uptake on return to dilute water. As well as being tolerant of extremely dilute waters, Rio Negro fish generally were fairly tolerant of low pH. Still, there were significant differences in sensitivity to pH among the species on the basis of degree of stimulation of Na(+) efflux at low pH. There were also differences in sensitivity to low pH of Na(+) uptake, and two species maintained significant rates of uptake even at pH 3.5. When fish were exposed to low pH in Rio Negro water instead of deionized water (with the same concentrations of major ions), the effects of low pH were reduced. This suggests that high concentrations of dissolved organic molecules in the water, which give it its dark tea color, may interact with the branchial epithelium in some protective manner.     

Patterns of ion regulation in acidophilic fish native to the ion-poor, acidic Rio Negro

The Na⁺ uptake mechanism of cardinal tetras Paracheirodon axelrodi displayed specialization for operation in dilute waters of the amazonian Rio Negro. Kinetic analysis revealed low K_m and high J_max values which ensure high rates of uptake even in very dilute waters. In contrast, Na⁺ uptake of angelfish Pterophyllum scalare did not appear to be specialized for dilute waters at all, with much higher K_m and lower J_max values. Na⁺ uptake in cardinal tetras was high and completely unaffected down to pH 3·5, while uptake in angelfish was much lower and progressively inhibited by dropping pH; it was completely shut down at pH 3·5. During chronic exposure to pH 4·0 and 3·5, angelfish showed no ability to restore Na⁺ uptake and at pH 3·5 all individuals died between day 3 and 6 presumably due to small, but steady loss of Na⁺. At low pH, both species displayed a strong ability to prevent stimulation of diffusive Na+ losses. In angelfish, the ability to control diffusive ion losses at low pH was related to a high branchial affinity for Ca²⁺. For cardinal tetras, the rate of Na⁺ loss appeared to be independent of water Ca²⁺ concentration. The specializations of cardinal tetras are similar to other characid fishes tested, but the results for angelfish reveal a new pattern of ion regulation in acidophilic species from the Rio Negro. The differences between the species may be the result of their different distributions, cardinal tetras are found in the central Rio Negro region while angelfish are more peripheral, or they may reflect phylogenetic differences.     

Seroepidemiological study of human hydatidosis, by means of an indirect hemagglutination test in Rio Negro County, X Region, Chile, 1989-1990

Rio Negro Country (40 degrees 48'-40 degrees 50' South lat.; 73 degrees 12'-73 degrees 13' West long.), is located in the province of Osorno, South of Chile. It has a population of 18,031 inhabitants, with 39% in rural areas. The basic economic activity is cattle raising (cows, pigs). According to reports, prevalence of human hydatidosis in 1988 was 11.1 per 100,000. In order to contribute to a better knowledge of human hydatidosis in Rio Negro County, an indirect hemagglutination test (IHAT) was performed to 509 randomized persons. Five (1.0%) individuals resulted positive.     

A new Apistogramma species (Teleostei, Cichlidae) from the Rio Negro in Brazil and Venezuela

Apistogramma diplotaenia sp.n. occurs in the upper and middle Rio Negro. The largest among 186 specimens studied is a 29.2 mm SL male, the largest female is 22.9 mm SL. Distinguishing characters include a unique colour pattern, consisting of two dark bands along the side which converge anteriorly and posteriorly. A comparative osteological study, including other species of Apistogramma and the genera Taeniacara and Apistogrammoides , indicates a progressive forwards loss of infraorbital ossicles and foramina among dwarf cichlids. The long, rod-like interarcual cartilage of Apistogramma, Apistogrammoides and Satanoperca possibly represents a plesiomorphic condition otherwise unknown among cichlids.     

A new species of Acestrocephalus (Characiformes: Characidae) from Venezuela

A new species of Acestrocephalus is described from 60 specimens collected in the Río Orinoco and Río Negro drainages, Venezuela. This species is distinguished from all other Acestrocephalus by the combination of the following characters: anal rays, 29-36; 63-71 perforated scales on the lateral line; 10-12 scales above and 9-12 below the lateral line; 39-52 teeth on the maxillary; 9-12 premaxillary teeth; 8-12 teeth in the inner row on the dentary; 5-7 gill rakers on the lower part of the first gill arch; humeral, peduncular and caudal blotch absent.     

Morphological and molecular evidence for two new species of Tetragonopterus (Characiformes: Characidae) from central Brazil

The combination of morphological and molecular data of Tetragonopterus species collected in the Rio Araguaia basin allows the recognition of two undescribed species that are presented in this article. These species are distinguished from their congeners (Tetragonopterus anostomus, Tetragonopterus argenteus, Tetragonopterus carvalhoi, Tetragonopterus chalceus and Tetragonopterus rarus) by characters related to the number and morphology of the teeth, the numbers of gill rakers on the upper and lower limbs of the first gill arch, the number of predorsal scales and the overall colour pattern. In addition, the analysis of mitochondrial DNA sequences identified an accentuated genetic distance between these two new species and their congeners. A discussion of the phylogenetic relationships within Tetragonopterus is provided.     

Notes on the vegetation of Amazonia I. A preliminary note on the origin of the open white sand campinas of the lower Rio Negro

The origin of the open areas of white sand campinas of the lower Rio Negro is discussed. Campinas are compared with the denser campina forests or caatingas of the upper Rio Negro. It is concluded that the campinas are areas of white sand forest cleared by Indians. Evidences from pottery shards and radiocarbon dating of charcoal deposited in the soil demonstrate that the campinas were occupied by Indians of the Guarita subculture around 800 A.D. The open campina areas show a gradual succession to more closed type of campina to campina forest, the climax on the white sand. The lack of a large number of endemic species also indicates a recent origin of the open areas. Recolonization after Indian clearing is extremely slow on white sand because of limiting factors such as nutrients and excessive drainage in the dry season.     

Eunotia amazonica sp. nov. (Bacillariophyta), a common stalk-forming species from the Rio Negro basin (Brazilian Amazon)

A new stalk-forming diatom was observed at high relative abundances on periphytic samples collected in the Rio Negro hydrographic basin (Brazilian Amazon) and is here described using light and scanning electron microscopy. We also present ecological preferences of the new species. Eunotia amazonica sp. nov. co-dominated periphytic samples collected during the rainy seasons of 2013 and 2014 near the city of Manaus (Amazonas, Brazil). The main diagnostic feature of the new species is the stalk-forming growth form (‘Cymbella-like’) illustrated here for the first time in the genus Eunotia Ehrenberg. Previous reports on growth forms in common European databases for this genus included colonial (‘ribbon-like’) but also ‘mobile’, ‘fixed by pads’ or ‘without structures of fixation’. We demonstrated that the three dominant Eunotia species in periphytic samples from the Rio Negro all exhibited distinct ‘growth forms’ or habits: Eunotia amazonica sp. nov. (stalked), Eunotia intricans Metzeltin & Lange-Bertalot (ribbon-like) and Eunotia rabenhorstiana (Grunow) Hustedt (branched-arborescent). The high diversity of species, many of which are unknown to science, as well as the poorly known life-forms and habits of the Eunotiaceae in the region, partially prevent the use of metrics based on life-form to assess ecological changes. Generic assumptions based on robust statistical methods may obscure reality and lead to biased conclusions of diatom community changes in poorly explored regions such as Neotropical freshwater rivers, where the Eunotiaceae are largely dominant, particularly in the Amazon basin.     

Use of Terra Firme Forest by Caicubi Caboclos,Middle Rio Negro,Amazonas, Brazil. A Quantitative Study

Use of Terra Firme Forest by Caicubi Caboclos, Middle Rio Negro, Amazonas, Brazil. A Quantitative Study. An ethnobotanical study was carried out with caboclos from the village of Caicubi, Roraima State, Brazil. This village is located between the Rio Negro and Rio Branco. The data were collected in 1 ha of terra firme forest and involved caboclo knowledge of the tree species with individuals dbh ≥ 10 cm. A total of 11 informants between 34 to 74 years of age were interviewed. The caboclos used 185 (98%) of the 189 species analyzed. The family with the highest use value for the community was Arecaceae. The species with the highest use value was Bertholletia excelsa. Arecaceae, Lecythidaceae, and Sapotaceae showed a wide variety of uses. The uses were grouped into eight categories; those with the highest use values were firewood, technology, and construction. The mean use value for species was 1.6. The most intensely used resources in the forest were wood, leaves, spines, and exudates.     

Protection by natural blackwater against disturbances in ion fluxes caused by low pH exposure in freshwater stingrays endemic to the Rio Negro

Stenohaline freshwater stingrays (Potamotrygon spp.) are endemic to the very dilute (Na(+), Cl(-), Ca2(+) 300 micromol L(-1) in reference water (low DOC) to about 100 micromol L(-1) in blackwater (high DOC). In reference water, both JNain and JClin were inhibited >90%, both JNaout and JClout more than doubled, and J(Amm) did not change at pH 4.0. In blackwater, the inhibition of influxes was attenuated, the increases in outflux did not occur, and J(Amm) increased by 60% at pH 4.0. Addition of 100 micromol L(-1) Ca(2+) to reference water prevented the increases in JNaout and JClout and allowed J(Amm) to increase at pH 4.0, which demonstrates that the gills are sensitive to Ca(2+). However, addition of Ca(2+) to blackwater had no effect on the responses to pH 4.0. Addition of commercial humic acid to reference water did not duplicate the effects of natural Rio Negro blackwater at the same DOC level; instead, it greatly exacerbated the increases in JNaout and JClout at low pH and prevented any protective influence of added Ca(2+). Thus, blackwater DOC appears to be very different from commercial humic acid. Biogeochemical modeling indicated that blackwater DOC prevents Ca(2+) binding, but not H(+) binding, to the gills and that the protective effects of blackwater cannot be attributed to its higher buffer capacity or its elevated Al or Fe levels. Natural DOC may act directly at the gills at low pH to exert a protective effect and, when doing so, may override any protective action of Ca(2+) that might otherwise occur.     

Ionic levels of the gallbladder bile of some teleosts from the Rio Negro, Amazon

The ionic levels of the gallbladder bile of 23 species of teleosts from the Rio Negro, Amazon, were analysed. Ionic levels of the gallbladder bile were variable according to the species and could not be related to the feeding habit or fullness of the gut.     

Wide but not impermeable: Testing the riverine barrier hypothesis for an Amazonian plant species

Wallace's riverine barrier hypothesis postulates that large rivers, such as the Amazon and its tributaries, reduce or prevent gene flow between populations on opposite banks, leading to allopatry and areas of species endemism occupying interfluvial regions. Several studies have shown that two major tributaries, Rio Branco and Rio Negro, are important barriers to gene flow for birds, amphibians and primates. No botanical studies have considered the potential role of the Rio Branco as a barrier, while a single botanical study has evaluated the Rio Negro as a barrier. We studied an Amazon shrub, Amphirrhox longifolia (A. St.‐Hil.) Spreng (Violaceae), as a model to test the riverine barrier hypothesis. Twenty‐six populations of A. longifolia were sampled on both banks of the Rio Branco and Rio Negro in the core Amazon Basin. Double‐digest RADseq was used to identify 8,010 unlinked SNP markers from the nuclear genome of 156 individuals. Data relating to population structure support the hypothesis that the Rio Negro acted as a significant genetic barrier for A. longifolia. On the other hand, no genetic differentiation was detected among populations spanning the narrower Rio Branco, which is a tributary of the Rio Negro. This study shows that the strength of riverine barriers for Amazon plants is dependent on the width of the river separating populations and species‐specific dispersal traits. Future studies of plants with contrasting life history traits will further improve our understanding of the landscape genetics and allopatric speciation history of Amazon plant diversity.     

Phylogeography of a flooded forest specialist fish from central Amazonia based on intron DNA: the cardinal tetra Paracheirodon axelrodi

1. Historic and extant landscape structures and environmental conditions are known to influence phylogeographic patterns and population histories in organisms from Amazonia. Recent work suggests that events of the Tertiary Period have played a significant role in generating biodiversity in this exceptionally rich but understudied region. However, species distributions and population structures are also affected by recent environmental and physical changes, especially within highly dynamic ecosystems. 2. The cardinal tetra is a small luminous fish native to the dynamic flooded forest ecosystems of the Rio Negro and Orinoco basins of South America. This very popular aquarium fish represents the single most important species in the ornamental fishery of the Rio Negro, an activity of high socio‐economic value for local riverine communities. Here we use a fine‐scale sampling regime and sequence data from the second intron of the Ribosomal protein S7 (S7 2) to investigate population structure, colonisation history and genealogical relationships in cardinal tetras of the Rio Negro. 3. High levels of S7 2 polymorphisms revealed phylogeographic patterns across several temporal settings that appear associated with the complex dynamics of the region. Our results suggest a long history of isolation and persistence of cardinal tetra populations in the headwaters and upper regions of the Rio Negro and recent events of colonisation within the incipient Rio Negro floodplain. These colonisation events were followed by recent population expansions likely facilitated by the establishment of the extensive Rio Negro floodplain, an anabranching ecosystem of Holocene age. 4. Our reconstruction of the phylogeographic history of cardinal tetras based on S7 2 intron sequence data reflects the complex influence of both geomorphological and climatic events through time in the Rio Negro basin. Our findings also indicate that in order to maintain the cardinal tetra fishery as a sustainable activity for rural Amazonians, the fishery should be restricted to the middle Rio Negro, the region of the basin where population replenishment is more likely to occur.     

Pilot Field Trial of the EG95 Vaccine Against Ovine Cystic Echinococcosis in Rio Negro,Argentina: Second Study of Impact

Background

Cystic echinococcosis (CE) is an important zoonotic disease caused by the cestode parasite Echinococcus granulosus. It occurs in many parts of the world where pastoral activities predominate, including the Rio Negro province of Argentina. Although CE control activities have been undertaken in the western regions of Rio Negro for more than two decades, the disease continues to remain prevalent in both the human and livestock animal populations. Vaccination of animal intermediate hosts of CE with the EG95 vaccine may provide a new opportunity to improve the effectiveness of CE control measures, although data are lacking about field application of the vaccine.

Aims

Evaluate the impact of EG95 vaccination in sheep on the transmission of Echinococcus granulosus in a field environment.

Methodology

Two trial sites were established in western Rio Negro province within indigenous communities. Vaccination of lambs born into one trial site was introduced and continued for 6 years. Prior to initiation of the trial, and at the end of the trial, the prevalence of CE in sheep was determined by necropsy. Weaned lambs received two injections of EG95 vaccine, approximately one month apart, and a single booster injection one year later. Vaccination was not implemented at the second trial site. A total of 2725 animals were vaccinated in the first year. Animals from this cohort as well as age-matched sheep from the control area were evaluated by necropsy.

Key results

Introduction of the vaccine led to a statistically significant in the number and size of hydatid cysts in comparison to the situation prior to the introduction of the vaccine, or compared to CE prevalence in the control area where the vaccine was not applied. The prevalence of infection in the vaccinated area was also significantly reduced by 62% compared to the re-intervention level, being lower than the prevalence seen in the control area, although the difference from the control area after the intervention was not significant possibly due to limitations in the numbers of animals available for necropsy.

Conclusions

Vaccination of sheep with the EG95 vaccine provides a valuable new tool which improves the effectiveness of CE control activities. Vaccination was effective even in a difficult, remote environment where only approximately half the lambs born into the communities were fully vaccinated.     

Molecular signature of the D-loop in the brown pencilfish Nannostomus eques (Characiformes, Lebiasinidae) reveals at least two evolutionary units in the Rio Negro basin, Brazil

The genetic variability of the brown pencilfish Nannostomus eques was studied, based on an analysis of sequences from the control region (1084 bp) of mitochondrial (mt)DNA in 125 individuals collected from eight tributaries along the upper (Açaituba, Miuá, Jaradi and Arixanã), middle (Demini), and lower (Jacundá, Maguari and Catalão) Rio Negro (Brazil). Phylogenetic inferences using mtDNA data from N. eques revealed two evolutionary units. Genetic distance between them ranged from 5·5 to 8·3% and differed by 8·5–11·8% from the sister species pencilfish Nannostomus unifasciatus. The time of divergence between the two evolutionary units was estimated to be the Middle Pliocene (c. 2·99 million years before present). Population genetic analysis (DNA polymorphism, AMOVA and Mantel test) showed high haplotype diversity (HD, >0·90) in each evolutionary unit, a strong population genetic structure in the Demini River that formed a monophyletic group and a correlation between genetic divergence and geographical distance in only one of these units (evolutionary unit 1). On the basis of molecular data, the rapids and waterfalls near São Gabriel da Cachoeira (Upper Rio Negro) were the main barriers to gene flow within evolutionary unit 1 in some localities. The emergences of the Branco River and the Anavilhanas Archipelago were apparently responsible for the discrepancy in distribution of the two evolutionary units, except at Jacundá, where the evolutionary units were sympatric. In view of the differences between the evolutionary units, N. eques cannot be treated as a single stock in the Rio Negro basin. These results may have important implications for the fishery management of this ornamental fish.     

Spatial distribution and habitat of the Anavilhanas Archipelago bird community in the Brazilian Amazon

This study is the first to present a quantitative survey of bird species occurring in the archipelago of Anavilhanas, located in the Rio Negro in the Brazilian Amazon and is part of the Anavilhanas Ecological Station. We asked whether bird community composition is similar among the islands, and between islands and areas dominated by the surrounding upland terra firme forest on the left (east) margin of the Rio Negro. The surveys were conducted in November and December of 1988, using two complementary methods with mist nets and boat transects. A total of 232 bird species was found for Anavilhanas including a survey done in 1998. The families Tyrannidae and Thamnophilidae showed the highest number of species (16.4% and 9.0% of the total respectively). Some species not well known or having limited distributions are relatively frequently encountered in the archipelago, such as Spizastur melanoleucus, Mitu tomentosa, Phaethornis rupurumii, Xiphorhynchus kienerii, Thamnophilus nigrocinereus, Myrmotherula klagesi, Myrmoborus lugubris, Pipra filicauda, and Cephalopterus ornatus. Hybrid Multidimensional Scaling (HMDS) ordination analysis indicated that the bird community composition is similar among islands. However, the bird community composition on the islands was significantly different from that in sites of terra firme forest at Rio Negro margins. Anavilhanas is a unique ecological system in the Amazon and has it own avifauna.     

Pollen sources used by species of Meliponini (Hymenoptera: Apidae) along the Rio Negro channel in Amazonas,Brazil

This work analyses the pollen stored by Meliponini bees whose nests were sampled along the Rio Negro channel, Amazonas, Brazil, during the final phase of the rainy season, which is also the time of pollen scarcity. From a total of 51 samples studied, 78 pollen types were identified, of which 39 were determined to species level. The pollen types were from 70 genera and 42 families. Based on the pollen records, a clustering analysis was performed, as well as the calculation of the trophic overlap index. The study demonstrates that the plants used by the bees do not depend on them for pollination in most cases; it rather suggests scarcity of pollen resources from the plants adapted to the pollination of Meliponini, and emphasises the ability of such bees to switch to new available resources. This work indicates a list of important plants for meliponiculture suitable for cultures near meliponaries.