Rio Negro Research Articles

New insights into the Cretaceous evolution of the Western Amazonian paleodrainage system

The geological history of the Amazon River is a complex story driven by geodynamic processes operating in the South American plate. In spite of recent research, the pre-Neogene structure of Amazon paleodrainage is still underconstrained. A recent study has suggested that the western Amazonian paleodrainage system was reversed, cratonic in origin during the Cretaceous. However, the extent and duration of this system are not well-constrained. To add new constraints, we investigated the sources of Cretaceous sedimentary rocks in the Brazilian Acre and Peruvian Madre de Dios basins, based on major and trace element concentrations, Sm–Nd isotopic compositions, and U–Pb detrital zircon dating. The late Cretaceous samples of the Acre Basin have εNd(0) values between −21.2 and −8.4 and zircon grains derived from terranes situated in the easternmost part of the Amazonian Craton: Ventuari–Tapajos (2.0–1.82 Ga) and Rio Negro–Juruena (1.82–1.54 Ga). In contrast, the Madre de Dios Basin samples have εNd(0) values ranging from −15.2 to −7.1 and a wide range of U–Pb zircon age distributions. The samples from the northern part of the basin (MD234 and MD238) are dominated by zircon ages between 0.9 and 1.3 Ga (Grenville/Sunsás, 30 %–43 %) and 0.5 and 0.7 Ga (Brazilian/Pampean, 26 %–16 %) with felsic provenance. The oldest MD234 sample also shows a dominant contribution from Paleozoic zircon (20 %). On the other hand, the samples from the southern part of the Madre de Dios Basin (samples MD-2019-4A; MD-2019-10; MD-2019-13; MD-2019-11D and MD-2019-12A) have U–Pb age distributions dominated by zircon ages between 0.9 and 1.3 Ga (Grenville/Sunsás, 30 %–45 %) and 1.54 and 1.3 Ga (Rondonia–San Ignácio, 16 %–43 %), pointing to a cratonic origin for these sedimentary rocks. To elucidate the distinction in provenance between the samples from the northern and southern parts of the Madre de Dios Basin, we suggest that a structural barrier (the Madidi Arch (?)) was active during the late Cretaceous. In this scenario, the northern part of the Madre de Dios Basin had similar sedimentary sources as the nearby basins like Huallaga, Bagua, Ucayali, and Marañón, whereas, in the southern part of the basin, sedimentation was influenced by local sources. Together with previously published studies, these data indicate that the continent-wide cratonic drainage developed between the Cenomanian and Maastrichtian in response to the Purus Arch uplift was probably driven by a geodynamic process related to the post-rift opening of the Atlantic Equatorial Ocean.

Fish on Fire: Shifts in Amazonian fish communities after floodplain forest fires

Abstract Severe droughts can lead to fires that cause massive tree mortality in even the wettest and most isolated Amazonian forests. After repeated fires, blackwater floodplain forests can remain in an open vegetation state of arrested succession that facilitates a transition towards a white‐sand ‘savanna‐like’ vegetation. These vegetation shifts, from closed‐canopy floodplain forests to open fire scars and eventually white‐sand savannas, may have profound implications for fish communities that depend on floodplain forests for food and recruitment. In turn, changes in fish communities may contribute to the arrested forest recovery after fires as fish are important seed dispersal agents for many floodplain tree species. To explore the impacts of floodplain forest fires on fish communities, we sampled fish in unburnt forests, fire scars, and white‐sand savannas in the middle Rio Negro basin (Brazil) during two consecutive flooding seasons. We compared the abundance, species richness, and the taxonomic and trophic composition of fish assemblages across the three habitat types. We found significant shifts in fish assemblages in fire scars compared to unburnt floodplain forests. Also, as fire scars increased in size, total fish biomass decreased strongly. Fish communities in unburnt floodplain forests seem to be characterized by a higher proportion of smaller and omnivorous fish species than fish communities in burned floodplain forests and white sand savannas. Fish assemblages in fire scars and white‐sand savanna were not significantly different. Synthesis and Applications. Amazonian fish communities change after floodplain forest fires. Unburnt forests have diverse fish communities, with a large proportion of unique and small omnivorous species. In contrast, carnivores and detritivores become more common in fire scars and white‐sand savannas formed after forest fires. Less omnivore fish after forest fires can reduce tree seed dispersal and forest regeneration, affecting ecosystem functioning and the services provided by Amazonian forests. Fish are also a primary source of food and income for people living in Amazonian floodplains. Preventing forest fires is therefore of fundamental importance for the conservation of Amazonian aquatic and terrestrial ecological communities as well as for the livelihood of people.

A new species of mailed catfish of genus Rhadinoloricaria (Siluriformes: Loricariidae: Loricariinae) from Rio Negro basin, Brazil.

During a recent collection expedition to the Rio Negro, in the state of Amazonas, Brazil, eight individuals of an unknown species were collected, with a combination of characteristics that placed the species in the genus Rhadinoloricaria. Furthermore, the presence of two autapomorphic characteristics, including numerous elongated papillae on the lower lip and unbranched barbelets on the margin of lower lip, suggests that it is a new species. From morphological and phylogenetic analyses, including the sequencing of specific genes to calculate the maximum likelihood analyses, coupled with osteological computed tomography (CT) scan analyses, the authors corroborated that the specimens represent a new species of Rhadinoloricaria, described in the present study.

A GUIDE TO FOSSILIFEROUS OUTCROPS FROM THE DEVONIAN OF MATO GROSSO DO SUL, CENTRAL-WEST BRAZIL

Mato Grosso do Sul has a significant area with Devonian outcrops containing fossils mainly of marine invertebrates, plants and, more rarely, fish fragments of the climax and impoverished Malvinoxhosan (= Malvinokaffric) fauna. Despite this, for a long time the state had a lack in studies related to the Devonian paleontology of the Paraná Basin, only gaining prominence from the 2010s onwards. Therefore, the objective of this work is to present a guide of the fossiliferous Devonian outcrops recognized so far in the state, which are located in the municipalities of Rio Negro, Rio Verde de Mato Grosso, Coxim and Pedro Gomes. The outcrops presented here represent a true geopaleontological heritage in situ. Divulge them is vital not only for their preservation, but also for the dissemination and appreciation of paleontological science among society in general.

(2950) Proposal to conserve the name Cacao sylvestris (Theobroma sylvestre) (Malvaceae: Byttnerioideae) with a conserved type

(2950) Proposal to conserve the name <i>Cacao sylvestris</i> (<i>Theobroma sylvestre</i>) (<i>Malvaceae</i>: <i>Byttnerioideae</i>) with a conserved type

In memoriam Klaus Kubitzki (1933–2022)

In memoriam Klaus Kubitzki (1933–2022)

Inexorable land degradation due to agriculture expansion in South American Pampa

From 1985 onwards, South America has undergone a major expansion in agriculture at the expense of native vegetation (for example, native Pampa grassland). As an emblematic crop, the surface area cultivated with soybeans has increased by 1,000% between 1990 and 2020 in Uruguay. The environmental consequences of this massive land-use conversion on soil degradation remain poorly documented, although agriculture expansion is projected to continue to increase in the coming years in South America. In this study, sediment cores were collected in reservoirs located downstream of two contrasted agricultural catchments draining the Rio Negro River (Uruguay) to reconstruct the sediment dynamics and the sources of erosion associated with this expansion. Results demonstrated the occurrence of two periods of acceleration of sediment delivery since the 1980s. The first period of acceleration was recorded in the mid-1990s and was related to afforestation programs. The second and larger acceleration phase was recorded after 2000 during the soybean crop expansion. This period was marked by a greater supply of sediment from the native grassland source, highlighting the impact of agriculture expansion at the expense of native vegetation. Conservation measures should therefore be urgently taken to preserve biodiversity and soil functions in this region. The impacts on soil degradation of the massive land-use conversion of South American Pampa grasslands to agriculture are not well documented. This study estimates, over the period 1982–2019, the impacts of such conversion on the sediment cascade and how soil and water resources are affected as a result.

Abundance estimates of southern right whales (Eubalaena australis) in Bahía San Antonio, Patagonia, Argentina

The abundance of southern right whales (Eubalaena australis) was estimated by the means of aerial line-transect surveys for the area of Bahía San Antonio, a bay located in the north-western region of the San Matías Gulf (40°50’S 64°50’W), Rio Negro, Patagonia Argentina. In total, seven aerial surveys were conducted in the first week of August and September 2009, September, October and November 2010, and August, September 2011. Survey effort equalled a total flight time of 12.4h, during which 200 whales were counted in 119 whale groups. Half of the encounters were solitary animals and 17% were mating groups. Corrected abundance estimates showed the highest amount of whales present in the bay during the month of September, with 85±71, 207±108 and 117±55 animals in 2009, 2010 and 2011 respectively. In adjacent months, less than half the amount of whales seemed to be present. The correction factor g(0)availability resulted 0.392±0.456. Perception bias was not accounted for. These aerial surveys resulted in the first estimates of southern right whale abundance in this north Patagonian bay and indicated a rather abrupt peak during the month of September. This being the peak month for right whale presence is consistent with data from other regions in the Southwest Atlantic, but data obtained in the other months remained scarce and thus results should be interpreted carefully. The complete absence of whales in the area during November 2010 and August 2011 raises further questions on the predictability of the whale’s presence in the area. Overall, more consistent aerial surveys should be conducted to accurately determine the annual and interannual evolution of southern right whale abundance in the study area.

A new giant titanosaur (Dinosauria, Sauropoda) from the Upper Cretaceous of Northwestern Patagonia, Argentina

Chucarosaurus diripienda gen. et sp. nov. is a new and large titanosaurian sauropod from the Neuquén Basin, Rio Negro Province, Patagonia. The specimen was discovered in the Upper Cretaceous strata of the Huincul Formation (middle Cenomanian–lower Turonian). It includes appendicular and relatively slender elements, with a femoral total length of about 1.9 m long. This taxon shows a unique combination of characters indicating that appendicular bones such as the femur, ischium and tibia, show a remarkable morphological variety, greater than previously described, and are morphologically informative as source of phylogenetic data. A cladistic phylogenetic analysis placed Chucarosaurus well nested within the Colossosauria clade.

Динамика рисков пространственной дезинтеграции Аргентины в начале XXI века

The aim of this study is to assess the risks of the spatial disintegration of Argentina, the determination of its dynamics (from 2006 to 2022) and the driving forces. According to the methodology used, spatial disintegration is manifested in the violation and destruction of system-forming relations between administrative-territorial units of the 1st order and is funded by a set of factors. The authors distinguish seven factors of spatial disintegration: historical, socio-economic, domestic, ethnocultural, transport, military-strategic and foreign policy, which make it possible to identify the risks of the country’s disintegration as a whole and to distinguish individual, most “implant” regions. The analysis showed that from 2006 to the present for Argentina, the risk of spatial disintegration increased slightly, but remains relatively low compare other previously studied Latin American countries (Mexico, Venezuela, Chile, Bolivia). The leading triggers of the spatial disintegration of Argentina were domestic political and socio-economic factors. The provinces with the greatest combination of risks were identified: Salta, Entre Rios, Tierra del Fuego, Neuquén, Corrientes, Formosa, Rio Negro, Misiones, which can be divided into “old” and “new disintegrators”, according to the dynamics of the number and quality of factors. The territorial drawing of the distribution of disintegration risks over the past 16 years has undergone changes: their increase for the northern and north-eastern border provinces, as well as the polarization of Patagonia, consisting in weakening the risks of the province of Chubut and Santa Cruz and their strengthening in Rio Negro. It is noted that on the basis of existing developments in neighboring countries, it makes sense to expand the space of the methodology and explore the border heterogeneous regions in Argentina and Chile.

Sarcopenia e fatores associados em pessoas idosas residentes em localidades rurais ribeirinhas na Amazônia

Abstract Objective To estimate the prevalence of signs suggestive of sarcopenia and its associated factors in an older rural riverside population of the Amazon. Method A cross-sectional household-based study was carried out from April to June 2021 involving the universe of older people (age ≥60 years) living in nine rural communities on the banks of the Rio Negro, Manaus city, Amazonas state, Brazil. Signs suggestive of sarcopenia were identified using the Sarcopenia Formulary combined with calf circumference. Sociodemographic aspects, physical performance (static standing balance, gait speed at usual pace, and chair sit and stand), handgrip strength and self-reported health conditions (hypertension, diabetes, stroke, chronic low-back pain and multimorbidity) represented the explanatory variables. Poisson regression with robust variance was used to assess factors associated with signs suggestive of sarcopenia. Results Data from 98 older individuals (55.1% male) with a mean age of 69.6±7.4 years were analyzed. Results revealed that 50.5% had low handgrip strength, 52.6% disability/low physical performance and 43.0% multimorbidity. Sarcopenia was identified in 28.9% of participants and associated with higher age (PR=1.1; 95%CI=1.1-1.1) and greater number of residents in the household (PR=1.2; 95%CI=1.0-1.3). Conclusion The findings of the study showed a high prevalence of signs suggestive of sarcopenia (28.9%) among the population of older people in rural riverside areas of the Amazon, where higher mean age and greater number of residents in the household increased the probability of occurrence of this clinical condition.

Canine parasitoses in north Patagonia (Argentina): comparison between different social and environmental factors.

In many countries, urban areas are commonly contaminated with canine feces that spread parasites, a situation related to the natural and social environment. Dogs having free access to public areas therefore constitutes a health risk. Because in Patagonia there are no records of city comparisons that consider the number of free-roaming dogs and the local environmental and socioeconomic characteristics, in this study we analyse and compare canine parasitoses in two cities of Rio Negro province, Argentina. Canine feces were collected from public areas of El Bolsón and Cipolletti cities and examined using enrichment methods, Kinyoun stain and immunoassay (Copro-Elisa). The total percentage of positive feces in El Bolsón was 68.95% and 16 parasite taxa being identified, whereas in Cipolletti the total positive feces was 41.1%, with 11 taxa. Both cities presented more helminth species than protozoans. The variables that explained the occurrence of all parasites were rainfall and socioeconomic stratum with the highest values being found in low-income areas.Soil moisture is conditioned by rainfall. This study highlights the presence of the zoonotic Echinococcus sp. in dogs in urban areas of the Rio Negro province. The occurrence of this parasite in Cipolletti is unexpected, given that this city is not considered an endemic zone for this disease, which is not included in local monitoring and control plans.

A growth model for Paleosuchus trigonatus (Crocodylia: Alligatoridae) from the Rio Negro predicts growth of individuals from the Xingu River, Brazil

&#x0D; &#x0D; &#x0D; &#x0D; Patterns of growth of crocodilians vary geographically within the same species, so models developed in one area may not predict size-age relationships in others. We used recapture data for three females and six males of Paleosuchus trigonatus from the Belo Monte hydroelectric dam area on the Xingu River to validate a growth model developed on a tributary of the Rio Negro. Individuals were recaptured between two and 10 years after marking (2012–2022). The data indicate that the monomolecular (von Bertalanffy by length) model is adequate to model growth of intermediate size animals. Recapture of one female after eight years indicates that the Rio Negro model can be used to model growth with accuracy for individuals from the Xingu River.&#x0D; &#x0D; &#x0D; &#x0D;

Population structure of mud flounder Paralichthys orbignyanus from the south-western Atlantic Ocean.

The mud flounder Paralichthys orbignyanus (Pleuronectiformes, Paralichthyidae) inhabits shallow waters of low salinities and mud bottoms in the temperate marine coastal regions of the Bonaerensean Ecoregion of the Argentinean Biogeographic Province in the south-western Atlantic Ocean. Specimens of P. orbignyanus were collected from Lagoa dos Patos (LDP) (southern Brazil), Mar Chiquita (MCH) and Marisol (MAR) both located in Buenos Aires (Argentina), and San Antonio Oeste (SAO) in the San Matías Gulf, Rio Negro (Argentina). A fragment of the mitochondrial DNA of the Control Region and seven microsatellite loci were characterized. In the Control Region, P. orbignyanus showed high variability, low nucleotide diversity, mild population expansion and a coalescence time of 35,000 years before the present. Flounders provided evidence of a genetic structure between the sampling sites LDP, MCH, MAR vs. SAO. On the other hand, P. orbignyanus displayed a lower to moderate contemporary genetic structure among all samples except between LDP and MCH. With no evidence of isolation by distance, this analysis supports a model of limited gene flow that is likely to be associated with a consistent larvae retention in all sampling sites. In addition, the present connectivity is ascribed to a lower migration process from SAO in the San Matías Gulf congruent with the prevailing littoral drift.

Conjectures and refutations: Species diversity and phylogeny of Australoheros from coastal rivers of southern South America (Teleostei: Cichlidae).

Morphological and genetic analyses of species of Australoheros focusing on those distributed in coastal rivers from the Rio de La Plata north to the Rio Buranhém, support recognition of 17 valid species in the genus. Eight species are represented in coastal rivers: A acaroides, A. facetus, A. ipatinguensis, A. oblongus, A. ribeirae, and A. sanguineus are validated from earlier descriptions. Australoheros mboapari is a new species from the Rio Taquari in the Rio Jacuí drainage. Australoheros ricani is a new species from the upper Rio Jacuí. Specimens from the Rio Yaguarón and Rio Tacuary, affluents of Laguna Merín, and tributaries of the Rio Negro, tributary of the Rio Uruguay are assigned to A. minuano pending critical data on specimens from the type locality of A. minuano. Australoheros taura is a junior synonym of A. acaroides. Australoheros autrani, A. saquarema, A. capixaba, A. macaensis, A. perdi, and A. muriae are junior synonyms of A. ipatinguensis. Heros autochthon, A. mattosi, A. macacuensis, A. montanus, A. tavaresi, A. paraibae, and A. barbosae, are junior synonyms of A. oblongus. Heros jenynsii is a junior synonym of A. facetus.

Diversity, multilingualism and inter-ethnic relations in the long-term history of the Upper Rio Negro region of the Amazon.

The Upper Rio Negro regional social system is made up of more than 30 languages belonging to six linguistic families. This results from socio-historical processes stretching back at least two millennia, which have built a system with different levels of autonomy and hierarchy associated with a mythical and ritual complex, and with social and linguistic exchanges. The analysis of these processes require an interdisciplinary outlook to understand the ways in which people from different linguistic families interacted and created it. More specifically, we ask how linguistic and cultural diversity have been created in the context of intense relations of multilingualism and inter-ethnic contact. To this end, we integrate perspectives from historical linguistics (regarding languages from the Tukanoan, Arawakan and Naduhup families) with archaeological data from the Amazonian past. Through this multidisciplinary approach, we seek to develop a linguistic-anthropological understanding of the dynamics shaping the region's diversity and inter-ethnic relations. We show that processes creating diversity are interrelated with changes in social histories, and are especially tied to the establishment of new forms of social organization as a result of pre-colonial inter-ethnic relations. This has led to the construction of various local multilingual ecologies connected to macro-regional processes in Amazonia.

Contextual and individual factors associated with self-reported tooth loss among adults and elderly residents in rural riverside areas: A cross-sectional household-based survey.

Tooth loss is an oral health condition with high prevalence and negative impact on quality of life. It is the result of the history of oral diseases and their treatment as well as provision of dental care and access to dental services. Socioeconomic characteristics are determinants of tooth loss and living in rural areas is also a risk factor for its incidence. To identify contextual and individual factors associated with self-reported tooth loss among adults and elderly people living in rural riverside areas. A cross-sectional household-based survey was conducted in 2019 with rural riverside communities on the left bank of the Rio Negro River, Manaus, Amazonas. These communities are covered by a fluvial health team and two riverside health teams. Interviews were conducted in a representative random sample of dwellers aged ≥ 18 years, using electronic forms to obtain information on oral health conditions, demographic and socioeconomic characteristics, and use of and access to health services. The outcome was self-reported tooth loss. After the descriptive analysis of the data, a multilevel Poisson regression analysis was performed to estimate the prevalence ratio for the outcome. Variables with p-value ≤0.20 in the bivariate analyses were included in the multiple analysis considering the hierarchy between individual and contextual variables in the multilevel model. Variables with p-value ≤0.10 were kept in the final model and the significance level adopted was 0.05. 603 individuals from 357 households were assessed (mean age 44.1 years). The average number of missing teeth was 11.2 (±11.6); 27.4% of individuals had lost more than 20 teeth (non-functional dentition) and 12.1% were completely edentulous. Contextual characteristic of primary healthcare offered was associated with the outcome. The tooth loss was lower in territories covered by riverside health teams. At individual level, tooth loss was greater in older individuals who had experienced dental pain over the past six months and whose sugar consumption was high. Black or brown individuals, individuals whose household income was higher, those who were on the Bolsa Família cash transfer program, those who consulted a dentist over the past year, and those who reported satisfaction with their teeth/oral health reported less tooth loss. Tooth loss was associated with contextual territorial factors related to the healthcare service and individual demographic, behavioral, socioeconomic, and service-related characteristics as well as self-perceived oral health conditions. The findings suggest that actions focused on the oral health of these populations involve not only changes in the healthcare service organization, but also intersectoral policies that contribute to reducing social inequalities.

Impacts of Climate Change on the Lives of Riverine Farmers on the Lower Rio Negro, Amazon

Global climate change, although gradual, is already clearly perceptible for the whole society; however, its impacts affect individuals and regions in diverse ways. Riverine communities in the Brazilian Amazon are highly vulnerable to this change, as seasonal hydroclimatic cycles govern their daily lives, integrate their way of life with the environment, and determine the organization of social and agricultural calendars. This work aimed to understand the impacts caused by climate change on the lives of riverine family farmers on the lower Rio Negro. Initially, through the analysis of changes in hydroclimatic trends and, later, through the description of perception, we tried to present the impacts on the ways of life to then know the climate adaptation strategies. The research was carried out in the state of Amazonas, in the riverine communities Tiririca, Marajá, Santo Antônio, and Terra Preta, located in the Rio Negro Sustainable Development Reserve, with 43 subjects through semi-structured and focus group interviews. Historical trends in the seasonality of the hydrological regime, precipitation, and temperature were analyzed, while qualitative data from environmental perception were analyzed using the technique of content analysis. Physical records of local climate variability and environmental perception are, in most cases, compatible and indicate that hydroclimatic cycles are changing. For the riverine people, the rains have been decreasing and there is unanimity in the perception that the increase in temperature is a reality that has affected their way of life at work, education, health, and food. Although communities have been developing spontaneous adaptive strategies to mitigate the effects of climate change, effective public policies need to reinforce these local responses to climate variability, contributing to the quality of life of populations.

Supplementary Materials and Supporting Files for Diversity, multilingualism and inter-ethnic relations in the long-term history of the Upper Rio Negro region from the Amazon

Supplementary Materials and Supporting Files for Diversity, multilingualism and inter-ethnic relations in the long-term history of the Upper Rio Negro region from the Amazon

Late Pleistocene landscape changes and habitat specialization as promoters of population genomic divergence in Amazonian floodplain birds.

Although vicariant processes are expected to leave similar genomic signatures among codistributed taxa, ecological traits such as habitat and stratum can influence genetic divergence within species. Here, we combined landscape history and habitat specialization to understand the historical and ecological factors responsible for current levels of genetic divergence in three species of birds specialized in seasonally flooded habitats in muddy rivers and which are widespread in the Amazon basin but have isolated populations in the Rio Branco. Populations of the white-bellied spinetail (Mazaria propinqua), lesser wagtail-tyrant (Stigmatura napensis) and bicolored conebill (Conirostrum bicolor) are currently isolated in the Rio Branco by the black-waters of the lower Rio Negro, offering a unique opportunity to test the effect of river colour as a barrier to gene flow. We used ultraconserved elements (UCEs) to test alternative hypotheses of population history in a comparative phylogeographical approach by modelling genetic structure, demographic history and testing for shared divergence time among codistributed taxa. Our analyses revealed that (i) all three populations from the Rio Branco floodplains are genetically distinct from other populations along the Amazon River floodplains; (ii) these divergences are the result of at least two distinct events, consistent with species habitat specialization; and (iii) the most likely model of population evolution includes lower population connectivity during the Late Pleistocene transition (~250,000 years ago), with gene flow being completely disrupted after the Last Glacial Maximum (~21,000 years ago). Our findings highlight how landscape evolution modulates population connectivity in habitat specialist species and how organisms can have different responses to the same historical processes of environmental change, depending on their habitat affinity.