Macrobrachium amazonicum (Decapoda, Palaemonidae): geographic distribution, new occurrences and biogeographic insights

The arowanas, fishes of Gondwanan origin, are represented in South America by the genus Osteoglossum. All species were initially reported as being exclusive to the Amazon region, with O. ferreirai restricted to the Negro River basin and O. bicirrhosum to the Amazon and Essequibo Rivers basin. Starting in the mid 1970's it was reported that O. ferreirai also occurs in the Orinoco River basin. In all regions the arowanas assumed significant socio-economic importance due to their popularity in the international ornamental fish trade, leading to over-exploitation of both species in some areas. The Orinoco populations are particularly heavily exploited, and thus conservation and management measures are needed. Both depend on the clarification of taxonomic status, and phylogenetic distinctness of the Orinoco populations. With the goal of molecularly characterizing the two species of Osteoglossum, and comparing populations of Osteoglossum from the Orinoco and Amazon basins, we characterized individuals sampled from eight localities, one in the Orinoco River basin and seven in the Amazon River basin. We sampled 39 individuals, obtaining 1004 base pairs, of which 79 were synapomorphies. Genetic distance between the two species calculated using the HKY + G model of molecular evolution was 8.94%. Intraspecific distances ranged from 0.42% in O. bicirrhosum to 0.10% in O. ferreirai. The genetic characterization confirmed the taxonomic status of O. ferreirai in the Orinoco basin, and suggested that its distribution in the Orinoco basin is unlikely to be the result of vicariance or natural dispersal, but rather an anthropic introduction.

The Neotropics contain one of the most diverse assemblages of freshwater fishes worldwide. Part of this diversity is shared between the Orinoco and Amazon basins. These basins have been separated for a long time due to the Vaupes Arch, rising between 10-11 Ma. Today, there is only one permanent connection between the Orinoco and Negro (Amazon) basins, known as the Casiquiare Canal. However, alternative corridors allowing fish dispersion between both basins have been proposed. The cardinal tetra (Paracheirodon axelrodi), the most important fish in the ornamental world market, is distributed in both basins. Here we investigated P. axelrodi phylogeography, population structure, and potential routes of migration and connectivity between the two basins. A total of 468 bp of the mitochondrial gene (COI), 555 bp of the nuclear gene fragment (MYH6), and eight microsatellite loci were analyzed. As a result, we found two major genetic clusters as the most likely scenario (K=2), but they were not discreetly distributed between basins. A gradient of genetic admixture was observed in Cucui and São Gabriel da Cachoeira, between the upper Negro River and the upper Orinoco. Samples from the middle-lower Negro River were highly structured. Cucui (Negro basin) was more similar to the Orinoco than to the rest of the Negro basin populations. However, substructure was also observed by the discriminant analysis, fixation indices and other hierarchichal structure analyses (K=3-6), showing three major geographic clusters: Orinoco, Cucui, and the remaining Negro basin. Unidirectional migration patterns were detected between basins: via Cucui toward Orinoco and via the remaining of the Negro basin toward Orinoco. Results from the Relaxed Random Walk analysis support a very recent origin of this species in the headwater Orinoco basin (Western Guiana Shield, at late Pleistocene) with a later rapid colonization of the remaining Orinoco basin and almost simultaneously the Negro River via Cucui, between 0.115 until about 0.001 Ma. Historical biogeography and population genetic patterns observed here for Cardinal tetra, seem to be better explained by river capture, physical, or ecological barriers than due to the geographic distance.

Tropical wetlands are one of the largest natural methane sources but lack of in-situ observations and uncertainty in wetland extent leads to large uncertainly. In this study we analyze the methane budget from three major river basins in South America: the Orinoco, the Amazon, and the Pantanal basins using two atmospheric inversions:  the CAMS-CH4inversion, which assimilates satellite and in-situ data and the CarboScope methane inversion system constrained by in-situ data only. We make a comparative analysis focusing on the seasonal cycle, interannual variability, and the total methane budget from 2000 to 2019.The budget difference in posterior estimates between CAMS-CH4 and CarboScope for these basins are as follows: Amazon Basin: -18.03 TgCH4/yr, Pantanal Basin: -11.65 TgCH4/yr, Orinoco Basin: -0.96 TgCH4/yr.  All together the total flux difference is -30.56 TgCH4/yr, indicating that CarboScope estimates larger total methane fluxes than the CAMS-CH4 inversion. Note that a similar difference (30.98 TgCH4/year) is also seen in the prior fluxes, suggesting that the optimization does not reduce the prior difference in the regions of interest.  While the Amazon Basin emits largest amount of methane, the Orinoco Basin exhibits the highest emissions per unit area, with 21.2 mgCH4/m²/day. In comparison, Amazon and Pantanal basins have emission of 19.26 mgCH4/m²/day and 13.36 mgCH4/m²/day. This shows the significant contribution of the smallest basin, in terms of methane flux density. Not surprisingly, both models indicate that wetlands are the primary methane source in the Amazon and Orinoco basins (~80%). In the Pantanal, CAMS-CH4 shows equal contributions from wetlands and anthropogenic sources, whereas CarboScope attributes dominance to anthropogenic emissions. Interestingly, seasonal patterns differ between the two models. In CAMS-CH4 there is a strong seasonality, with maximum methane emissions occurring during the wet season across all basins, in CarboScope, there is a double-peak in the Amazon Basin during March (wet) and August (dry). Finally, we investigate the inundation patterns and their relationship to methane emissions trends in these basins, as well as the factors influencing interannual variability to enhance our understanding of the processes driving these emissions.

Late Pleistocene sloths were widely distributed and present in a diversity of habitats in South, Central, and North America and some Caribbean Islands. Late Pleistocene sloths include 27 genera in four families Megatheriidae, Megalonychidae, Mylodontidae, and Nothrotheriidae. There is no consensus on the number of valid species. Some sloths have wide geographic distributions and are present on multiple continents while others have a much smaller distribution. Our knowledge of the paleoecology and natural history of the different sloths varies greatly depending on their relative abundance. The wide distribution of sloths and adaptations to different habitats results in several “sloth” faunas with different taxonomic compositions. These generalized faunas can be distinguished geographically as Temperate North America (five genera), Southern Mexico and Central America (five genera), Northern South America (two genera), West Coast of South America (four genera), the Andes and Altiplano (four genera), Brazilian Intertropical Region (nine genera), Pampas-Patagonia and the Caribbean Islands (Cuba, Hispaniola, and Puerto Rico, four genera). Some genera may occur in multiple regions but are represented by different species. These regions also have differences in other mammalian taxa, so the sloths are often in ecological competition with different megaherbivores or preyed on by different carnivores.

Thirty‐four genera belonging to the Gondwanian subfamily Atalophlebiinae are known from the Neotropics. Development of the lower Central American isthmus was marked only by dispersal of Gondwanian Atalophlebiinae from South America into Central America. No member of the Laurasian subfamily, the Leptophlebiinae, has dispersed from North America into Central or South America. The Antilles were colonized entirely by Atalophlebiinae from South and Central America. Genera of Neotropical Atalophlebiinae are placed into one of two faunal components: either the Patagonian Shield, South Andean, Cold‐Adapted Genera; or the Guiana & Brazilian Shields, Warm‐Adapted Genera. The 10 Patagonian Shield Genera are primarily associated with cold‐water streams of southern South America. Secondary diversification has occurred in the southern coastal mountains of Brazil, and at high elevations in the central and northern Andes. Phylogenetically, Patagonian Shield Genera are related to diverse genera on several Gondwanian conti...

Detecting vulnerability of humid tropical forests to multiple stressors

We analyze the observed relationship between sea surface temperatures (SSTs) over the Atlantic Ocean and the normalized difference vegetation index (NDVI) in the Orinoco and Amazon basins. Monthly correlations between anomalies of NDVI and SSTs are computed for different regions of the Atlantic Ocean. We also use a mixture of observations and reanalysis products to analyze lagged correlations. Our results show that during August–September (i.e., the dry-to-wet transition season), changes in NDVI in the central Amazon and the so-called Arc of Deforestation are associated with precedent changes in the SSTs of the tropical North Atlantic (TNA) and the Caribbean (CABN) during March–June. Anomalous warming of the CABN and TNA generates changes in surface winds and atmospheric moisture transport in the region, decreasing precipitation, with consequent decreases of soil moisture, moisture recycling, and NDVI. An increase in TNA and CABN SSTs during March–June is also associated with an increase of NDVI over the northern Orinoco during June (i.e., the wet season). Unlike in the southern Amazon, precipitation and soil moisture in the Orinoco basin do not exhibit significant changes associated with SSTs. By contrast, atmospheric moisture recycling and transport increase with warmer SSTs in the TNA. Therefore, for the Orinoco, the link between SSTs and NDVI appears to be related not to changes in precipitation but to changes in moisture recycling. However, the causality between these changes needs to be further explored. These findings highlight the contrasting responses of the Amazon and Orinoco basins to Atlantic temperatures and the dominant role of atmospheric moisture transport linking these responses.

This study assesses the improvement of the latest Coupled Model Intercomparison Project Phase 6 (CMIP6) over Coupled Model Intercomparison Project Phase 5 (CMIP5) for precipitation simulation. Precipitation simulations under different future climate scenarios are also compared in this work. The results show that: 1) CMIP6 has no overall advantage over CMIP5 in simulating total precipitation (PRCPTOT) and maximum consecutive dry days (CDD). The performance of CMIP6 increases or decreases regionally in PRCPTOT and consecutive dry days. But it is slightly worse than CMIP5 in simulating very wet days (R95pTOT). 2) Comparing the trend test results of CMIP5 and CMIP6 in the future, there are more areas with significant trend based on Mann–Kendall test in CMIP6 compared with that of CMIP5. The differences in PRCPTOT are mainly found in Amazon Basin and Western Africa. The differences between the R95pTOT trends mainly noticeable in South America and Western Africa, and the differences in CDD are mainly reflected in Central Asia, Sahara Desert and central South America. 3) In Southern South America and Western North America, the PRCPTOT changing rate of CMIP6 in the future under various scenarios is always greater than that of CMIP5; in Alaska, Western Africa, Southern Africa, the PRCPTOT changing rate of CMIP6 in the future under various scenarios is always less than that of CMIP5. In Southern South America, the R95pTOT changing rate of CMIP6 in the future under various scenarios is always greater than that of CMIP5; in Alaska, East Asia, North Asia, the R95pTOT changing rate of CMIP6 in the future under various scenarios is always less than that of CMIP5. In almost half of the regions, the CDD changing rate of CMIP6 is less than that of CMIP5 under all scenarios, namely Australia, Amazon Basin, Southern South America, Central America, Western North America, Central North America, Eastern North America, Central Asia, Tibet.

BackgroundParasite prevalence and diversity are determined by the distribution of hosts and vectors and by the interplay among a suite of environmental factors. Distributions of parasite lineages vary based on host susceptibility and geographical barriers. Hemoparasites of the genera Haemoproteus and Plasmodium have wide distributions, and high prevalence and genetic diversity within perching birds (Order Passeriformes). The rufous-collared sparrow (Zonotrichia capensis) is widely distributed in Central and South America across an immense diversity of environments from sea level to more than 4000 meters above sea level. It therefore provides an excellent model to investigate whether altitudinal and latitudinal gradients influence the distribution, prevalence and diversity of haemosporidian parasites, their population structure and the biogeographical boundaries of distinct parasite lineages.ResultsWe assembled samples from 1317 rufous-collared sparrows spanning 75 locales from across Central and South America (between 9.5°N and 54°S; 10–4655 meters above sea level). We used DNA sequence data from a fragment of the mitochondrial cytochrome b gene (cytb) of Haemoproteus and Plasmodium from 325 positive samples and found prevalences of 22 and 3%, respectively. Haemoproteus exhibited a higher prevalence than Plasmodium but with comparatively lower genetic diversity. We detected a relationship of Plasmodium and Haemoproteus prevalence with altitude and latitude; however, altitude and latitude did not influence parasite diversity.ConclusionsParasite lineages showed a phylogeographical boundary coincident with the Andes Mountains, although we also observed a north-south disjunction in Peru for Haemoproteus. Haemosporidian distribution was not homogeneous but differed based on latitude and altitude. This is most probably due to environmental factors that have influenced both vector distribution and abundance, as well as parasite development. Our study provides key insights on the distribution of haemoparasite lineages and parasite dynamics within hosts.

Biogeographical and geological evidence for a smaller, completely‐enclosed Pacific basin in the Late Cretaceous: a comment

In the Amazon and Orinoco basins, mercury has been released from artisanal and industrial gold mining since the Colonial time, as well as a result of deforestation and burning of primary forest, that release natural deposits of methyl mercury, affecting the local aquatic vertebrate fauna. This study reports the presence of mercury in river dolphins' genera Inia and Sotalia. Mercury concentrations were analysed in muscle tissue samples collected from 46 individuals at the Arauca and Orinoco Rivers (Colombia), the Amazon River (Colombia), a tributary of the Itenez River (Bolivia) and from the Tapajos River (Brazil). Ranges of total mercury (Hg) concentration in muscle tissue of the four different taxa sampled were: I. geoffrensis humboldtiana 0.003-3.99mgkg-1ww (n = 21, Me = 0.4), I. g. geoffrensis 0.1-2.6mgkg-1ww (n = 15, Me = 0.55), I. boliviensis 0.03-0.4mgkg-1ww (n = 8, Me = 0.1) and S. fluviatilis 0.1-0.87mgkg-1ww (n = 2, Me = 0.5). The highest Hg concentration in our study was obtained at the Orinoco basin, recorded from a juvenile male of I. g. humboldtiana (3.99mgkg-1ww). At the Amazon basin, higher concentrations of mercury were recorded in the Tapajos River (Brazil) from an adult male of I. g. geoffrensis (2.6mgkg-1ww) and the Amazon River from an adult female of S. fluviatilis (0.87mgkg-1ww). Our data support the presence of total Hg in river dolphins distributed across the evaluated basins, evidencing the role of these cetaceans as sentinel species and bioindicators of the presence of this heavy metal in natural aquatic environments.

Urbanization and land use changes alter the nitrogen (N) cycle, with critical consequences for continental freshwater resources, coastal zones, and human health. Sewage and poor watershed management lead to impoverishment of inland water resources and degradation of coastal zones. Here we review the N contents of rivers of the three most important watersheds in South America: the Amazon, La Plata, and Orinoco basins. To evaluate potential impacts on coastal zones, we also present data on small- and medium-sized Venezuelan watersheds that drain into the Caribbean Sea and are impacted by anthropogenic activities. Median concentrations of total dissolved nitrogen (TDN) were 325 μg L−1 and 275 μg L−1 in the Amazon and Orinoco basins, respectively, increasing to nearly 850 μg L−1 in La Plata Basin rivers and 2000 μg L−1 in small northern Venezuelan watersheds. The median TDN yield of Amazon Basin rivers (approximately 4 kg ha−1 yr−1) was larger than TDN yields of undisturbed rivers of the La Plata and Orinoco basins; however, TDN yields of polluted rivers were much higher than those of the Amazon and Orinoco rivers. Organic matter loads from natural and anthropogenic sources in rivers of South America strongly influence the N dynamics of this region.

Special issue editorial. Freely available on the publisher's website - access full text via the Official URL link.

The fourth biennial meeting of the International Biogeography Society (IBS) in Merida, Yucatan in January 2009 represented a double opportunity for Mexican biologists. First, it fostered the integration of the large community of Mexican biogeographers with the activities of the IBS. Second, the meeting allowed us to welcome a large number of delegates from distant parts of the world who were able to visit what has been considered an obligate destination for nature lovers and cultural tourists alike: the Yucatan peninsula. As Edward O. Wilson pointed out, besides economic power every country has two additional and important types of wealth: cultural and natural. Cultural richness is a naturally embedded component of the Mexican way of life.

Climate scenarios are important information for water planning, but, in some cases, they disagree with recent climate alterations, which affects their robustness and reliability. Robustness evaluation can help identifying areas that should be prioritized by in water sector adaptation to climate change. Although crucial, this kind of analysis has been overlooked in most climate change assessments, for instance in South America. This study assesses the robustness and reliability of river discharge scenarios by comparing them with observed and modelled data. Areas where current changes and scenarios agree are more likely to experience changes and, therefore, water planners should pay special attention to them. Tocantins-Araguaia, São Francisco, Western Northeast Atlantic and upper La Plata basins agreed with a discharge decrease, indicating that climate change should be prioritized in planning. Orinoco and upper-western Amazon basins showed strong disagreement between recent and projected discharge alterations, with positive change in last decades, showing that scenarios in these regions should be carefully interpreted. With this, water planners could interpret Northeastern and upper-central South America as presenting more likely scenarios in comparison to Amazon and Orinoco basins.