Instituto Nacional de Limnología

How diversity is structured has been a central goal of microbial ecology. In freshwater ecosystems, selection has been found to be the main driver shaping bacterial communities. However, its relative importance compared with other processes (dispersal, drift, diversification) may depend on spatial heterogeneity and the dispersal rates within a metacommunity. Still, a decrease in the role of selection is expected with increasing dispersal homogenization. Here, we investigate the main ecological processes modulating bacterial assembly in contrasting scenarios of environmental heterogeneity. We carried out a spatiotemporal survey in the floodplain system of the Paraná River. The bacterioplankton metacommunity was studied using both statistical inferences based on phylogenetic and taxa turnover as well as co-occurrence networks. We found that selection was the main process determining community assembly even at both extremes of environmental heterogeneity and homogeneity, challenging the general view that the strength of selection is weakened due to dispersal homogenization. The ecological processes acting on the community also determined the connectedness of bacterial networks associations. Heterogeneous selection promoted more interconnected networks increasing β-diversity. Finally, spatiotemporal heterogeneity was an important factor determining the number and identity of the most highly connected taxa in the system. Integrating all these empirical evidences, we propose a new conceptual model that elucidates how the environmental heterogeneity determines the action of the ecological processes shaping the bacterial metacommunity.

The impact of the widely used herbicide glyphosate has been mainly studied in terrestrial weed control, laboratory bioassays, and field studies focusing on invertebrates, amphibians, and fishes. Despite the importance of phytoplankton and periphyton communities at the base of the aquatic food webs, fewer studies have investigated the effects of glyphosate on freshwater microbial assemblages. We assessed the effect of the commercial formulation Roundup using artificial earthen mesocosms. The herbicide was added at three doses: a control (without Roundup) and two treatments of 6 and 12 mg/L of the active ingredient (glyphosate). Estimates of the dissipation rate (k) were similar in the two treatments (half-lives of 5.77 and 7.37 d, respectively). The only two physicochemical parameters showing statistically significant differences between treatments and controls were the downward vertical spectral attenuation coefficient kd(lambda), where lambda is wavelength, and total phosphorus concentration (TP). At the end of the experiment, the treated mesocosms showed a significant increase in the ratio kd(490 nm)/k(d)(550 nm) and an eightfold increase in TP. Roundup affected the structure of phytoplankton and periphyton assemblages. Total micro- and nano-phytoplankton decreased in abundance in treated mesocosms. In contrast, the abundance of picocyanobacteria increased by a factor of about 40. Primary production also increased in treated mesocosms (roughly by a factor of two). Similar patterns were observed in the periphytic assemblages, which showed an increased proportion of dead: live individuals and increased abundances of cyanobacteria (about 4.5-fold). Interestingly, the observed changes in the microbial assemblages were captured by the analysis of the pigment composition of the phytoplankton, the phytoplankton absorption spectra, and the analysis of the optical properties of the water. The observed changes in the structure of the microbial assemblages are more consistent with a direct toxicological effect of glyphosate rather than an indirect effect mediated by phosphorus enrichment.

Due to the great climatic variety and the peculiar north–south orographic distribution, Argentinean lake systems include a wide diversity of aquatic environments. The deepest lakes are situated in the Andean Patagonia and Tierra del Fuego, and range from ultraoligotrophic to oligotrophic. Patagonian Plateau lakes are shallower than Andean lakes and usually range from mesotrophic to eutrophic. All lakes in the Chaco‐Pampa Plain are very shallow and range from eutrophic to hypertrophic or salt lakes. Most of the lakes situated in the central–western and northwestern arid regions are reservoirs or salt lakes, and range from mesotrophic to eutrophic. More than half of the northwestern reservoirs have very low dissolved oxygen concentrations in the hypolimnion during mid‐summer. Argentina has more than 400 lakes with surface area >5 km 2 , but for some of them not even major ion data are available. In order to synthesize and to extract general characteristics and patterns, issues have been selected which adequately reflect the character of the lake environment in Argentina. We divided Argentina according to geographical regions into six major divisions: Puna, Chaco‐Pampa Plain, Peri‐Pampean Sierras, Andean Patagonia, Patagonian Plateau, and Misiones Plateu and Brazilian Shield‐related systems. Most of the lakes situated in Patagonia are undisturbed lakes. However, the Chaco‐Pampa Plain lakes are usually lightly impacted by agricultural operations. Moreover, most of the reservoirs located in the Argentinean arid ‘corridor’ are highly impacted by agriculture. Other lakes in both north and south Argentina range from salt lakes, through dark humic‐stained lakes and large river floodplain lakes, to dilute high altitude glacial lakes. Argentina still has a larger proportion of its lake waters in natural conditions. However, expected developments for natural resources indicates that Argentinean goals for lake water management should include the preservation of some proportion of pre‐European natural lake environment, and the evolution of a stable, managed lake environment in the more developed regions.

En la presente contribución se brinda una versión actualizada del “Catálogo de las plantas vasculares del Cono Sur” de Sudamérica (Argentina, sur del Brasil, Chile, Paraguay y Uruguay), once años después de la publicación de su versión original. Se brinda un detalle de las Lycophyta, Monilophyta, Gymnospermae y Angiospermae (Monocoyledoneae y Dicotyledoneae) registradas para el área hasta julio de 2019. Este catálogo incluye, en la actualidad, 289 familias, 2813 géneros y 18931 especies. Este número de especies es superior en 1238 al registrado en la versión original, lo cual ilustra sobre la gran cantidad de novedades florísticas y taxonómicas registradas para el área y la importancia de matener esta información actualizada. Es digno de destacar que más del 40% de las especies presentes en el Cono Sur son endémicas de esta área. En este trabajo se aportan tablas que resumen la información florística para el Cono Sur y para cada uno de los países que lo integran, discriminando por grandes grupos taxonómicos, familias y géneros; se hacen comparaciones respecto a la versión original, se especifican las familias y géneros endémicos del área y también aquellos introducidos; finalmente se analizan las relaciones florísticas entre los países involucrados. Adicionalmente, se incluyen apéndices en formato digital, que corresponden a la nueva versión catálogo, completo y actualizado, y al resumen florístico para cada país.

In many countries of the Global South, aquatic ecosystems such as streams, rivers, lakes, and wetlands are severely impacted by several simultaneous environmental stressors, associated with accelerated urban development, and extreme climate. However, this problem receives little attention. Applying a DPSIR approach (Drivers, Pressures, State, Impacts, Responses), we analyzed the environmental impacts and their effects on urban hydrosystems (including stagnant waters), and suggest possible solutions from a series of case studies worldwide. We find that rivers in the Global South, with their distinctive geographical and socio-political setting, display significant differences from the Urban Stream Syndrome described so far in temperate zones. We introduce the term of ‘Southern Urban Hydrosystem Syndrome’ for the biophysical problems as well as the social interactions, including the perception of water bodies by the urbanites, the interactions of actors (e.g., top-down, bottom-up), and the motivations that drive urban hydrosystem restoration projects of the Global South. Supported by a synthesis of case studies (with a focus on Brazilian restoration projects), this paper summarizes the state of the art, highlights the currently existing lacunae for research, and delivers examples of practical solutions that may inform UNESCO’s North–South–South dialogue to solve these urgent problems. Two elements appear to be specifically important for the success of restoration projects in the Global South, namely the broad acceptance and commitment of local populations beyond merely ‘ecological’ justifications, e.g., healthy living environments and ecosystems with cultural linkages (‘River Culture’). To make it possible implementable/practical solutions must be extended to (often poor) people having settled along river banks and wetlands.

Over the past 4 decades there has been a growing concern for the conservation status of elasmobranchs (sharks and rays). In 2002, the first elasmobranch species were added to Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Less than 20 yr later, there were 39 species on Appendix II and 5 on Appendix I. Despite growing concern, effective conservation and management remain challenged by a lack of data on population status for many species, human−wildlife interactions, threats to population viability, and the efficacy of conservation approaches. We surveyed 100 of the most frequently published and cited experts on elasmobranchs and, based on ranked responses, prioritized 20 research questions on elasmobranch conservation. To address these questions, we then convened a group of 47 experts from 35 institutions and 12 countries. The 20 questions were organized into the following broad categories: (1) status and threats, (2) population and ecology, and (3) conservation and management. For each section, we sought to synthesize existing knowledge, describe consensus or diverging views, identify gaps, and suggest promising future directions and research priorities. The resulting synthesis aggregates an array of perspectives on emergent research and priority directions for elasmobranch conservation.

The present study aimed to evaluate the biological effects triggered by the application of a current-use mixture of pesticides (the herbicide glyphosate, the insecticide bifenthrin, BF, and the fungicides azoxystrobin, AZ, and cyproconazole, CYP) on two native fish (Markiana nigripinnis and Astyanax lacustris) inhabiting a rice field. We analyzed pesticide residues in water, sediment and fish samples 21 days before and after a fumigation event. Additionally, organismic indices, oxidative stress and neurotoxicity biomarkers in fish at both sampling periods were compared. After fumigation, glyphosate, BF, AZ and CYP were detected in water and sediment samples, being also bioaccumulated in both fish species. A decreasing condition factor in A. lacustris and a higher liver somatic index in M. nigripinnis were observed as well. Overall, results showed that, after the application of the pesticide mixture, antioxidant mechanisms failed to prevent oxidative damage in the liver and gills of M. nigripinnis. Meanwhile, A. lacustris showed a different response: an inhibition of the antioxidant defenses without tissue lipid oxidative damage. Furthermore, acetylcholinesterase activity after spraying was significantly reduced in brain and muscle tissues of A. lacustris and in the brain of M. nigripinnis. Our results show that current-use pesticides, like glyphosate, BF, AZ and CYP, pose health risks on native fish populations inhabiting rice fields.

Channel bifurcations associated with bars and islands are important nodes in braided rivers and may control flow partitioning and thus affect downstream confluences, as well as the formation and dynamics of bars. However, the morphodynamic processes associated with bar formation are poorly understood, and previous studies have largely concerned laboratory experiments, small natural streams, or numerical analyses with large Froude numbers, high slopes, and low Shields stresses. In these cases, the morphologic changes at bifurcations are relatively rapid, with predominant bed load transport and the suspended load playing a minor role. In this paper, the evolution of the flow structure and suspended bed sediment transport along four expansion‐diffluence units in the Rio Paraná, Argentina, are described. The Rio Paraná is a large multichannel river with a bed composed of medium and fine sands and possesses low Froude numbers and high suspended bed material transport. Primary and secondary flow velocity components were measured with an acoustic Doppler current profiler (ADCP) along the expansion‐diffluence units, and the backscatter signal of the ADCP was calibrated to allow simultaneous measurements of suspended bed sediment concentrations. The interactions between these variables show that the cores of primary flow velocity and suspended bed sediment concentration do not necessarily follow the thalweg at the bifurcation and that inertial effects on the suspended bed sediment may influence the morphodynamics of bar formation. It is suggested that changes in flow stage, as well as the presence of vegetation, may further increase the deposition of suspended bed sediment at the bar head. This study suggests that the ratio of suspended bed material to bed load is an important factor controlling the morphodynamics of bifurcations in large sand bed braided rivers.

Abstract The idea of an area of endemism implies that different groups of plants and animals should have largely coincident distributions. This paper analyses an area of 1152 000 km 2 , between parallels 21 and 32°S and meridians 70 and 53°W to examine whether a large and taxonomically diverse data set actually displays areas supported by different groups. The data set includes the distribution of 805 species of plants (45 families), mammals (25 families), reptiles (six families), amphibians (five families), birds (18 families), and insects (30 families), and is analysed with the optimality criterion (based on the notion of endemism) implemented in the program NDM/VNDM. Almost 50% of the areas obtained are supported by three or more major groups; areas supported by fewer major groups generally contain species from different genera, families, or orders. © The Willi Hennig Society 2011.

Summary 1. Shallow lakes and ponds contribute disproportionally to species richness relative to other aquatic ecosystems. In‐lake conditions (e.g. presence of submerged plants) seem to play a key role in determining diversity, as has been demonstrated for temperate lakes. When water quality deteriorates and turbidity increases, conditions in such lakes are affected drastically resulting in a loss of diversity. However, it is not clear whether subtropical lakes show the same pattern and whether the richness of all groups reacts similarly to environmental changes. 2. Our aim was to analyse the main factors explaining patterns of species richness in plankton, fish and submerged macrophyte assemblages in both turbid and clear subtropical shallow lakes. We analysed abiotic and biotic features of 18 subtropical, small‐ to medium‐sized, shallow lakes along the Uruguayan coast. We compared both turbid and clear ecosystem states and evaluated the relative variance explained by the factors measured. 3. Variables describing lake and catchment morphology, as well as the percentage of the water column occupied by submerged macrophytes (%PVI) and water turbidity, had strong effects on taxon richness. Interestingly, individual biotic groups had dissimilar richness patterns. Macrophyte %PVI decreased with increasing lake area, while fish species richness showed the opposite pattern. Phytoplankton species richness increased with macrophyte %PVI, while the zooplankton richness pattern varied depending on the taxonomic group considered. 4. Overall, our results indicate that, as found for temperate lakes, a greater submerged plant cover promotes higher species richness in several groups, and that this may overwhelm the otherwise expected positive effect of lake size on species richness. On the other hand, small‐bodied zooplankton predominated in lakes with high plant abundance. Our findings concur with recent studies, indicating that refuge capacity of aquatic plants might be weaker in (sub)tropical than in temperate shallow lakes. 5. The extremely high plant cover, frequently observed in warm lakes, could potentially lead to different richness patterns in some groups. This conclusion has important consequences for local managers and conservationists.

Summary Despite a general recognition that benthic macroinvertebrates respond to changes in hydrological connectivity within floodplain ecosystems, no consensus about patterns in community structure and ecosystem processes across large scales and different climates has yet been established. Such knowledge is necessary since anthropogenic activities continue to alter the natural hydrogeomorphology of large floodplains, with most consequences for aquatic communities remaining unknown. Using information from six large rivers located in four different climate regions (humid subtropical, maritime temperate, Mediterranean and dry semi‐arid), we compared benthic macroinvertebrate responses along lateral gradients of hydrological connectivity. We tested hypotheses related to differences among climate regions and to similar hydrological constraints within any one climate. The large geographical scale covered by this study provides the first comprehensive comparison of aquatic community patterns across hydrological gradients under different climatic settings. Multivariate ordinations demonstrated a higher overlap of trait community composition (50% variance explained by the first two axes) than taxonomic composition (15%) among floodplains, displaying high interclimate trait stability. The taxonomy‐based ordination separated the subtropical floodplain, with an average 86% of non‐insect taxa, from the insect‐dominated temperate, Mediterranean and semi‐arid floodplains (with >50% insect abundance). In the trait‐based ordination, large body size (60% of organisms >4 cm) and long lifespan duration (80% of organisms) discriminated the subtropical from the other five studied floodplains. Across a gradient of lateral connectivity, linear mixed effect ( LME ) models supported seven of 15 hypotheses, which suggests remarkably consistent macroinvertebrate patterns in floodplains regardless of the climate regime. Taxon and trait richness were positively related and peaked at sites of intermediate hydrological connectivity. Our predictions about the feeding guilds of macroinvertebrates (e.g. that shredders and scrapers would be more abundant in connected channels, and predators and deposit feeders at isolated sites) were more strongly supported by the data than those about life history (e.g. plurivoltinism and short lifespan would be better represented in connected channels). This difference was related to the influence of extended periods of hydrological disconnection as disturbance in addition to flooding. Trait stability across hydrological connectivity provides a meaningful ecological context for the comparison of the macroinvertebrate benthos among climatic zones, where taxonomic composition differs strongly. In addition, trait similarities and dissimilarities found in this study suggest that large‐scale biogeographical filters do operate on communities, resulting in different trait combinations in temperate and Mediterranean floodplains when compared to semi‐arid and subtropical environments. The extent to which global macroecological factors (i.e. climate, dispersal history) and local biotic and abiotic factors (i.e. drought frequency, habitat structure, water chemistry) contribute to this difference requires further investigation.

Abstract The Reynolds Functional Groups (RFG) classification scheme is an informative and widely used method in ecological studies of freshwater phytoplankton. It clusters species with similar traits, as well as common environmental sensitivities and tolerances. However, researchers face the difficulty to classify species into RFG because it relies in expert opinion, taxonomical knowledge and environmental information, which are not always accessible. Thus, a step forward is to build general statistical models to classify species into RFG. Under the hypothesis that an organism's response to environmental conditions determines their functional traits, here represented by the RFG, we predict that morphology and classification into broad taxonomic groups will explain RFG independently from environmental information and expert knowledge. To evaluate the predictive ability of morphological traits (e.g. volume) and taxonomic affiliation (e.g. chroococcal Cyanobacteria) as discriminant variables of RFG, we compiled 1,300 species (264 waterbodies) and applied Random Forest (RF) and Classification and Regression Trees (CART). We divided the data to train the models and test their performance. RF successfully classified species into the 28 RFG (only c . 10% test error) with an average individual RFG success rate of 84.6 (range = 33%–100%). This is a relatively high percentage of success from an ecological point of view. It suggests that the selected variables are able to reconstruct the RFG and represent well environmental preferences, without including information about local environmental conditions as classifiers. Our results reinforce the functional basis of the RFG and support both morphological traits and taxonomic classification as good proxies of phytoplankton responses to environmental conditions. A dichotomous key based on the CART was constructed, and an R code to classify species into the RFG is freely available. This work may help users to classify species into the RFG, including those that were not previously listed in the Reynolds classification system.

La erosion de los suelos es la causa principal de las perdidas irreversibles del potencial productivo de los suelos en la mayoria de los pastizales naturales. En el nordeste de Patagonia, el aumento de la erosion de los suelos ha estado estrechamente asociado al aumento de la cobertura de arbustos en las estepas herbaceas o arbustivas-herbaceas. Nosotros empleamos lluvia simulada para determinar la tasa de infiltracion y la produccion de sedimentos en parches de estepas herbaceas, arbustivas-herbaceas y arbustivas del sitio ecologico Punta Ninfas. Las coberturas de suelo desnudo y de gravas fueron mayores y la cobertura de mantillo menor en la estepa arbustiva respecto a las estepas arbustiva- herbacea y herbacea. En los espacios entre arbustos de la estepa arbustiva, la densidad aparente fue mayor y la macroporosidad y la materia organica fueron menores (P 0.05) que en los monticulos debajo de los arbustos y en las estepas arbustivaherbacea y herbacea. La tasa de infiltration fue un 60 y un 65% mas baja en la estepa arbustiva que en las estepas herbacea y arbustiva-herbacea, respectivamente. Por el contrario, la produccion total y la concentracion de sedimentos fueron mas altas (P s 0.05) en la estepa arbustiva comparado con las estepas herbacea y arbustiva-herbacea. La cobertura de gravas fue la variable que mejor predijo la tasa de infiltracion y la produccion de sedimentos. El contenido de materia organica de los sedimentos, mayormente mantillo, fue similar en la estepa arbustiva y la arbustiva-herbacea y en ambas mayores (P 0.05) que en la estepa herbacea. La remocion de mantillo por el escurrimiento superficial posiblemente represente uno de los procesos que provocan la transicion de la estepa arbustiva-herbacea a la estepa arbustiva. Las altas tasas de remocion de sedimentos, principalmente mantillo, de los espacios entre arbustos de la estepa arbustiva pueden limitar la recuperacion natural de las propiedades fisicas a hidrologicas de los suelos. Estos parches degradados no pueden captar las lluvias incidentes, limitando asi las posibilidades de recuperacion de los pastos perennes y favoreciendo la dominancia de los arbustos.

Monthly oviposition activity and the seasonal density pattern of Aedes aegypti were studied using larvitraps and ovitraps during a research carried out by the Public Health Ministry of Salta Province, in Tartagal, Aguaray and Salvador Mazza cities, in subtropical Argentina. The A. aegypti population was active in both dry and wet seasons with a peak in March, accordant with the heaviest rainfall. From May to November, the immature population level remained low, but increased in December. Ae. aegypti oviposition activity increased during the fall and summer, when the relative humidity was 60% or higher. Eggs were found in large numbers of ovitraps during all seasons but few eggs were observed in each one during winter. The occurrence and the number of eggs laid were variable when both seasons and cities were compared. The reduction of the population during the winter months was related to the low in the relative humidity of the atmosphere. Significant differences were detected between oviposition occurrences in Tartagal and Aguaray and Salvador Mazza cities, but no differences in the number of eggs were observed. Two factors characterize the seasonal distribution pattern of Ae. aegypti in subtropical Argentina, the absence of a break during winter and an oviposition activity concomitant of the high relative humidity of the atmosphere.

Valid fish species identification is essential for biodiversity conservation and fisheries management. Here, we provide a sequence reference library based on mitochondrial cytochrome c oxidase subunit I for a valid identification of 79 freshwater fish species from the Lower Paraná River. Neighbour-joining analysis based on K2P genetic distances formed non-overlapping clusters for almost all species with a ≥99% bootstrap support each. Identification was successful for 97.8% of species as the minimum genetic distance to the nearest neighbour exceeded the maximum intraspecific distance in all these cases. A barcoding gap of 2.5% was apparent for the whole data set with the exception of four cases. Within-species distances ranged from 0.00% to 7.59%, while interspecific distances varied between 4.06% and 19.98%, without considering Odontesthes species with a minimum genetic distance of 0%. Sequence library validation was performed by applying BOLDs BIN analysis tool, Poisson Tree Processes model and Automatic Barcode Gap Discovery, along with a reliable taxonomic assignment by experts. Exhaustive revision of vouchers was performed when a conflicting assignment was detected after sequence analysis and BIN discordance evaluation. Thus, the sequence library presented here can be confidently used as a benchmark for identification of half of the fish species recorded for the Lower Paraná River.

Abstract Aim The main drainages of the Plata Basin – the Paraná, Paraguay and Uruguay rivers – begin in tropical latitudes and run in a north–south direction into subtropical–temperate latitudes. Consequently, the biota of these rivers has tropical elements that contrast with temperate biomes through which the rivers run. We apply a panbiogeographical approach, to test whether the large rivers of the Plata Basin have a differential influence on distributional patterns of tropical snakes in subtropical and temperate latitudes of South America. Location Subtropical and temperate sections of the major Plata Basin rivers, South America. Methods We compared the individual tracks of 94 snake taxa. The track analysis consisted of: (1) plotting the localities of each taxon on maps, (2) connecting the localities of each taxon using a minimal geographical proximity determinant of the ‘individual tracks’, and (3) superimposing the individual tracks to determine generalized tracks. To detect tropical snakes that reach higher latitudes through the rivers we used the preferential direction of distribution concept. For each taxon we measured the angular deviations between the line of its individual track and the course of the rivers in a 100 × 100 km scaled grid. Average angular values < 45° indicated a positive association with the rivers. Results Thirty‐five of 94 taxa showed distributions associated with the major rivers of the Plata Basin, including fauna from distinct biogeographical lineages, supported by the occurrence of five generalized tracks as follows: (1) the Paraguay–Middle Paraná, (2) the Paraguay–Paraná fluvial axis, Upper Paraná and Middle Paraná to Upper Delta, (3) the Lower Paraguay, Paraná and Uruguay rivers, excluding the sectors High Paraná and High Uruguay, (4) the Uruguay River and Upper Paraná, and (5) the High Paraná. The Atlantic species occurred with significantly higher frequency in the Uruguay River and High Paraná river sections, the Amazon species were found with significantly higher frequency in the Paraguay and Middle Paraná sections, and the species with a Pantanal distribution were found in all sections. Main conclusions The observed distributional patterns may be explained by the interaction of ecological, geographical and historical factors. Previous authors have developed ecological (hydrological or environmental similarity) or dispersalist (effect of rivers as migration routes) explanations. The coincidence between generalized tracks and past geomorphological events that caused displacements and changed relationships between the Paraguay, Paraná and Uruguay river sections supports hypotheses involving the strong influence of historical factors in the present configuration of tropical snake distribution in temperate latitudes.

In this study, we examined the influence of demography and social context on mother-offspring conflict in wild black and gold howler monkeys (Alouatta caraya) inhabiting two nearby sites in northern Argentina, one comprising continuous forest and one fragmented forest. These sites differed in population density (3.25 vs. 1.04 individuals/ha), degree of home range overlap between neighboring groups (70 vs. 31%), and rate of intergroup encounters (2 vs. 0.02-1 encounters/day), though not in interbirth interval or rate of infant mortality. During a 27-month study (September 2008 through November 2010), we observed 37 mother-offspring dyads across the two sites. We found a very similar pattern of mother-offspring conflict in both populations; specifically, the sites did not differ in any of the variables used to characterize the mother-offspring relationship (the time spent in contact, the rate at which the mother makes and breaks contact, the rate at which the infant breaks contact, the rate of maternal rejection, and signs of infant distress) except one (the rate at which the infant makes contact). Although mother-offspring conflict is a dynamic process that varies over time, our results suggest that the different demographic and social contexts found at the two study sites did not have a marked effect on quantitative aspects of the mother-offspring relationship in these populations of black and gold howlers. Finally, this study suggests that the environmental variability (ecological, demographic, and social traits) leads to a set of strategies used both by infants and mothers with a main goal of conflict resolution, with mothers specifically aiming to cope with the tradeoff between current and future reproduction.

The occurrence of abnormalities in amphibians has been reported in many populations, and its increase could be related to environmental pollution and habitat degradation. We evaluated the type and prevalence of abnormalities in 5 amphibian populations from agroecosystems with different degrees of agricultural disturbance (cultivated and reference areas). We detected 9 types of abnormalities, of which the most frequent were those occurring in limbs. The observed prevalence of abnormality in assessed populations from cultivated and reference areas was as follows: Rhinella fernandezae (37.1 and 10.2%, respectively), Leptodactylus latrans adults (28.1 and 9.2%) and juveniles (32.9 and 15.3%), and Hypsiboas pulchellus (11.6 and 2.8%). Scinax granulatus populations did not show abnormalities. Pseudis minuta, which was only detected in the reference area, exhibited a prevalence of 13.3%. For R. fernandezae, L. latrans, and H. pulchellus, generalized linear mixed models showed that prevalence of abnormalities was significantly higher (p < 0.05) in cultivated than in reference areas. L. latrans juveniles were more vulnerable to abnormalities than adults (p < 0.05). The presence of abnormalities in some species inhabiting different agroecosystems suggests that environmental stress factors might be responsible for their occurrence. While we detected pesticides (endosulfan, cypermethrin, and chlorpyrifos) and lower dissolved oxygen levels in ponds of the cultivated area, no data are currently available on how other factors, such as injuries from predators and parasite infections, vary by land use. Further research will be necessary to evaluate possible causes of abnormalities detected in the present study mainly in the context of factor interactions.

Abstract In this paper, the sediment budget at the confluence of the Paraná–Paraguay Rivers is updated on the basis of new suspended sediment concentration data, obtained during the 1990s at carefully located cross‐sections, after the construction of several large reservoirs. With these data, it was possible to estimate that the suspended sediment load transported by the Upper Paraná River had decreased by 60% due to the influence of the dams. This decrease occurred in spite of the influence of climate change across the Upper Paraná and Paraguay basin, which increased the precipitation and surface runoff. As a consequence of these anthropogenic and natural processes, the Bermejo River (the main source of wash load to the system) accounts for an increasing proportion of the sediment transport along the middle and lower reaches of the Paraná River. The Paraná River currently transports about 120 × 10 6 t year −1 of wash load, with nearly 90% of this being supplied by the Bermejo. The contribution from the Bermejo is now about 35% larger than its contribution during the 1970s, when it accounted for approximately 60% of the sediment load of the Paraná River. These changes that have occurred over the last 30 years have enhanced the natural asymmetrical distribution of solid and water discharges in the Paraná River basin. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Abstract The central provinces of Argentina are characterized by the presence of a high number of shallow lakes, located in endorheic basins, many of which have elevated salinities as well as eutrophic or hypereutrophic condition. The zooplankton of four saline shallow lakes of the province of La Pampa was studied on a monthly basis during a 2‐year period to determine its temporal and spatial variation. The surface of these shallow lakes (&lt;2.5 m depth) varied between 56.8 and 215.9 ha, and some have from 8.4 to 20.8 g · l –1 . The more saline lakes have “clear” water and the less saline lakes “turbid” water. Fishes, Jenynsia multidentata , were present in only two lakes during the last two months of the studied period. The zooplankton was composed of 17 taxa of Rotifera, 5 taxa of Cladocera and 4 taxa of Copepoda. The low diversity and the faunistic composition are characteristic of saline environments. Although the studied lakes share 38% of the species, the faunistic similarity was higher between the two least saline lakes. The lowest diversity was found in the two most saline lakes. All four shallow lakes were characterized by their very high zooplankton density, especially in the least saline lakes (&lt;80000 ind · l –1 ). The abundance is significantly correlated with the water transparency but not with salinity. The zooplankton temporal variation was characterized by the alternation of macro‐ and microzooplankton, probably regulated by competition and intrazooplanktonic predation. In each lake, the spatial abundance distribution of the macro‐ and microzooplankton was homogeneous. It was related to the shallow depht of the lakes and their polymictic condition. The Scheffer model on alternative states in shallow lakes acknowledges that it cannot be applied to saline lakes because Daphnia , the main responsible for the clear water state, is not tolerant to high salinity. Our study shows that the most saline lakes, where the halophylic Daphnia menucoensis is abundant, have also the most clear waters. Another difference that we found with regards to the mentioned model is that, in turbid lakes, it could not have had a top‐down control on macrozooplankton exerted by fishes because in these lakes fishes were practically absent. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)