Neotropical Basins Research Articles

A multi-level approach using Gambusia affinis as a bioindicator of environmental pollution in the middle-lower basin of Suquía River

The Suquía River middle-lower basin (Córdoba, Argentina) is subjected to a strong anthropogenic impact because it receives pollutants from different sources. The main goal of this study was to evaluate the introduced fish species Gambusia affinis as a bioindicator of environmental pollution in the middle-lower basin of the Suquía River. The assessment was performed by measuring biomarkers at different levels of biological organization, at two sampling sites (before and after Córdoba city), and at dry and wet seasons. Water quality evaluation was made through a water-quality index (based on physico-chemical parameters), heavy-metals and pesticides concentrations in water. The water quality varied between sampling sites, showing the most degraded conditions downstream Córdoba city. The same pattern of variation was detected in the biomarkers studied, mainly in: gill and liver histopathological indexes, copulatory organ (gonopodium) morphology and vitellogenin expression in males and females. The present study characterized the environmental conditions in the middle-lower basin of the Suquía River and revealed the low freshwater quality at the most polluted site. Although G. affinis is an introduced species, it could be considered a good sentinel of water resource quality of invaded Neotropical basins. Our results demonstrated the importance of addressing the environmental quality monitoring through an integrated analysis of water quality parameters together with histological, morphological and molecular parameters. Thus, our study provides a good model for application in other basins of South America.

Fish farming as the main driver of fish introductions in Neotropical reservoirs

Several human activities may result in or facilitate species introductions. In aquatic environments, species introductions are often associated with the construction of dams. In this study, we use reservoirs of the Neotropical region as a model to determine the main causes of fish species introductions. We compiled information on non-native fish species present in reservoir ichthyofauna surveys in the past 14 years and classified these species based on their probable reason for introduction (vector). Fish farming activities introduced approximately 7.6-fold more species in reservoirs than the other vectors identified. The matrix of the number of fish species per vectors explained the greatest proportion of the composition of non-native assemblages, whereas the geographic distance and age of the reservoir explained few of these variations. The non-native ichthyofauna composition varied among Neotropical basins and can be explained by the different sets of species introduced by the companies managing the reservoirs. Although power companies have banned stocking with non-natives, fish farming in the Neotropical region continues to use non-native species, and these species are occupying water bodies, especially reservoirs.

Concordant biogeographic patterns among multiple taxonomic groups in the Mexican freshwater biota.

In this paper we analyse the degree of concordance in species richness and taxonomic distinctness (diversity) patterns among different freshwater taxonomic groups in order to test three long held patterns described in Mexican freshwater biogeography: 1. The aquatic biota of Mexico includes two distinct faunas, a rich Neotropical component in the south and a south-eastern region and a less rich Nearctic component towards central and northern latitudes of the country. 2. A hotspot of species richness and diversity has been recorded in the Usumacinta, including the Yucatan Peninsula. 3. The presence of two distinct biotas in Mexico, an eastern one distributed along the Gulf of Mexico slope, and a western one associated to the Pacific versant. We use species richness and taxonomic distinctness to explore patterns of diversity and how these patterns change between zoogeographical regions. This paper points out a clear separation between Neotropical and Nearctic drainage basins but also between eastern (Gulf of Mexico) and western (Pacific) drainage basins. Present data gives additional empirical support from freshwater biota for three long held beliefs regarding distributional patterns of the Mexican biota. The neotropical basins of Mexico are generally host to a richest and more diversified fauna, that includes more families, genera and species, compared to the less rich and less diverse fauna in the nearctic basins.

Desempeño productivo del coporo con dietas isotópicas

Los peces detritívoros son la base de la cadena alimentaria y están ampliamente distribuidos en las cuencas neotropicales, los Prochilodus son representativos de este grupo y el bocachico llanero o coporo (Prochilodus mariae) es de interés comercial en acuicultura. Para evaluar el desempeño productivo en alevinos de coporo con dietas isotópicas, fueron conformados dos tratamientos: dieta comercial (δ13C -20.93±0.34) y dieta experimental (δ13C -24.6±0.9) suministradas durante sesenta días. Parámetros de peso medio, longitud media estándar, ganancia de peso (GP), tasa de crecimiento específico (TCE) y factor de conversión alimenticia (FCA) fueron determinados. La contribución y fraccionamiento de la dieta fueron estimados a partir de las lecturas isotópicas en muestras de músculo. El peso y longitud estándar del coporo fue superior en el tratamiento de la dieta comercial (DC). En los parámetros GP y TCE hubo diferencia significativa (P<0.05) entre tratamientos, siendo el tratamiento DC siempre superior frente a la dieta experimental (DE). La contribución relativa de la DC y DE fue de 59.2 y 53.4% respectivamente, en cuanto que el mayor fraccionamiento de la dieta en carbono y nitrógeno fue de la DE en 1.97 y 1.14%0 respectivamente. La relación entre la contribución de la dieta y la ganancia de peso fue más eficiente para DC en términos de carbono, contrariamente, la eficiencia del nitrógeno fue con DE. Aunque la contribución de las dietas fue inferior a 60%, ambas contribuyeron a mejorar el desempeño del coporo.

Taxonomic Distinctness and Richness of Helminth Parasite Assemblages of Freshwater Fishes in Mexican Hydrological Basins

In this paper, we analyse the distributional patterns of adult helminth parasites of freshwater fishes with respect to the main hydrological basins of Mexico. We use the taxonomic distinctness and the variation in taxonomic distinctness to explore patterns of parasite diversity and how these patterns change between zoogeographical regions. We address questions about the factors that determine the variation of observed diversity of helminths between basins. We also investigate patterns of richness, taxonomic distinctness and distance decay of similarity amongst basins. Our analyses suggest that the evolution of the fauna of helminth parasites in Mexico is mostly dominated by independent host colonization events and that intra - host speciation could be a minor factor explaining the origin of this diversity. This paper points out a clear separation between the helminth faunas of northern - nearctic and southern - neotropical components in Mexican continental waters, suggesting the availability of two distinct taxonomic pools of parasites in Mexican drainage basins. Data identifies Mexican drainage basins as unities inhabited by freshwater fishes, hosting a mixture of neotropical and nearctic species, in addition, data confirms neotropical and neartic basins/helminth faunas. The neotropical basins of Mexico are host to a richest and more diversified helminth fauna, including more families, genera and species, compared to the less rich and less diverse helminth fauna in the nearctic basins. The present analysis confirms distance - decay as one of the important factors contributing to the patterns of diversity observed. The hypothesis that helminth diversity could be explained by the ichthyological diversity of the basin received no support from present analysis.

Contrasting taxonomical and functional responses of stream invertebrates across space and time in a Neotropical basin

The structure of the EPT group (Ephemeroptera, Plecoptera and Trichoptera) reflects changes operating on the underlying freshwater system. We study the structure of the EPT assemblages inhabiting a Neotropical basin with mountain rain forests. Taxonomic richness and functional diversity are two relevant indicators of that struc- ture. We measured real biological traits rather than using trait classifications arising from the Northern hemisphere, allowing us to more accurately calculate functional diversity metrics in these Neotropical streams. We also formal- ized a new approach to measuring functional dissimilarity. Our main scope is to know the effects of space (altitudi- nal zonation) and time (seasonality) on the behavior of both diversity indexes. We find complementarities between them, suggesting that the replacement in taxonomic composition is a process decoupled from the replacement in trait composition. While the taxonomic richness of sites in the dry season differs from the richness in upland sites sampled during spates, the functional diversity allows us to differentiate lowland sites sampled during spates from other sites. We hypothesize that functional diversity goes down in lowland sites because of the anthropogenic pres- sure on the riparian area. We additionally stress that the knowledge of functional diversity contributes to the better design of conservation strategies.

Maize pollen concentrations in Neotropical lake sediments as an indicator of the scale of prehistoric agriculture

We evaluated the potential of maize pollen concentrations in lake sediment profiles to serve as indicators of the extent of prehistoric agriculture in neotropical lake basins using records from a network of five sediment cores recovered from Laguna Zoncho, Costa Rica. The watershed of this small (0.75 ha) lake in the Diquís archaeological region has a c. 3000 year history of prehistoric agriculture and subsequent forest recovery, as documented through previous studies of pollen, charcoal, diatoms, and phosphorus fractions in a single core recovered from the center of the lake. In our new network of cores, we compared maize pollen concentrations with two independent proxies for the scale of agriculture in the same cores: abundance of organic matter (OM), which is an indicator of soil erosion, and bulk sediment stable carbon isotope ratios of organic matter (δ13COM), which reflect the proportion of forested and cleared land within the watershed. In none of the five cores did maize pollen concentrations correspond with either OM or δ13COM, suggesting that sedimentary maize pollen concentrations are not sensitive to the scale of maize agriculture in small neotropical watersheds. We found maize pollen in relatively high concentrations in two of the four cores taken near the lakeshore, but the others contained little or no maize pollen. The core from the center of the lake consistently recorded maize pollen, a finding that we attribute to sediment-focusing processes.

Use of the BEAST model for biomonitoring water quality in a neotropical basin

The use of predictive models in Neotropical basins is relatively new, and applying these models in large basins is hindered by the lack of ecological, geographical, and social-environmental knowledge. Despite these difficulties, we used data from the das Velhas River basin to apply the BEAST (Benthic Assessment of SedimenT) methodology to evaluate and classify the level of environmental degradation. Our two main objectives were to modify and implement the BEAST methodology for use in biomonitoring programs of Brazilian basins, and to test the hypothesis that a gradient of environmental degradation determines a gradient in the structure and composition of benthic macroinvertebrate assemblages. We evaluated 37 sites: 8 in the main river, 15 in the main tributaries with different impact levels, and 14 in tributaries with minimally disturbed conditions (MDC). The BEAST model allowed us to classify 16 test sites: two as natural, four as altered, three as highly altered, and seven as degraded. Our results indicated degradation of the das Velhas River basin near its urban areas. The BEAST model indicated that the pollution gradient found among the sites generated a gradient of the macroinvertebrate assemblages, corroborating the hypothesis.

Conserver les spécificités de l'ichtyofaune guyanaise

The French Guiana freshwaters present a specific richness comparable or even greater than in the other Neotropical basins, but with a high degree of endemism. The authors describe two types of specialized ichthyofauna in French Guiana, the first west of Kourou River and the second to the east. Knowledge of the ichthyofauna from upper basins is still incomplete, and as a result any risk of diminishing their biodiversity through indiscriminate human activities should be avoided. Strict conservation measures must be enacted to protect and manage this original ichthyological heritage.