Trophic structure of a floodplain fish assemblage in the upper Amazon basin, Bolivia / Estructura trófica de un ensamblaje de peces en la cuenca alto-Amazónica, Bolivia

Abstract Amazonian fish assemblages are typically high in species diversity and trophic complexity. Stable isotopes are valuable tools to describe the trophic structure of such assemblages, providing useful information for conservation and ecological management. This study aimed at estimating the relative contribution of the different basal carbon sources to the diet of primary consumer fishes (herbivores and detritivores), and determining the trophic position (TP) of the dominant fishes from each trophic guild (herbivores, detritivores, invertivores and piscivores). For this purpose we analyzed stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in potential food sources, and muscle tissue of fishes in five oxbow lakes located in the floodplain of River Ichilo, Bolivia. Terrestrial plants and C3 aquatic macrophytes were the major carbon source contributing to the diet of herbivorous fishes, whereas particulate organic matter (POM) contributed more to the diet of detritivore fishes. In general, C4 aquatic macrophytes contributed little to the diet of herbivores and detritivores. However, we found a relatively high contribution of C4 macrophytes (28 %) to the diet of the herbivores Mylossoma duriventre and Schizodon fasciatus. We found a good agreement between our estimated TP values and the trophic group assigned based on diet composition from literature. The herbivore M. duriventre was at the bottom of the food web, being the baseline organism (TP = 2). The remaining primary consumers (herbivores and algivore/detritivores) exhibited relatively high TP values (2.3-2.9), probably due to their opportunistic feeding behavior. Omnivore/invertivore species studied displayed TP values near the 3.0 value expected for secondary consumers. Piscivore fishes were at the top TP, with TP values varying from 3.3 (Serrasalmus spilopleura and Serrasalmus rhombeus) to 3.8 (Pseudoplatystoma fasciatum). The fact that detritivore fishes, the most abundant food source for piscivores, occupy relatively high TPs determines that food chains in these particular Amazonian floodplains are longer than previously thought. Rev. Biol. Trop. 66(3): 1258-1271. Epub 2018 September 01.

Resumen Los ensamblajes de peces amazónicos presentan alta diversidad y complejidad trófica. La descripción de su estructura trófica proporciona información útil para su manejo. Con el fin de estimar la contribución de las fuentes básicas de carbono en la dieta de los consumidores primarios, y determinar la posición trófica (PT) de las especies dominantes de peces de cada gremio, analizamos isótopos estables de carbono (δ13C) y nitrógeno (δ15N) en las fuentes de carbono y en músculo de peces, de la llanura de inundación del río Ichilo. Las plantas terrestres y las macrófitas C3 fueron las mayores fuentes de carbono en la dieta de los peces herbívoros, mientras que la materia orgánica particulada contribuyó más a la dieta de los detritívoros. Las macrófitas C4 contribuyeron poco a la dieta de herbívoros y detritívoros, excepto para Mylossoma duriventre y Schizodon fasciatus, en las que encontramos una contribución relativamente alta (28 %). Encontramos una buena relación entre los valores estimados de PT y el gremio trófico asignado en la literatura. El herbívoro M. duriventre estuvo en la base de la red trófica (PT = 2). Los restantes consumidores primarios mostraron valores de PT relativamente altos (2.3 - 2.9), probablemente debido a sus hábitos alimenticios oportunistas. Las especies omnívoras/invertívoras mostraron valores cercanos a 3. Los peces piscívoros estuvieron en la cima de la red trófica, con PT que variaron entre 3.3 (Serrasalmus spilopleura y Serrasalmus rhombeus) y 3.8 (Pseudoplatystoma fasciatum). Estos datos sugieren que las cadenas tróficas en llanuras de inundación amazónicas, son más largas de lo que se suponía.

Stable isotope evidence for trophic overlap of sympatric Mexican Lake Chapala silversides (Teleostei: Atherinopsidae: Chirostoma spp)

We explore the trophic role that a diverse sympatric group of fishes in the genus Chirostoma play in a large, shallow lake in central Mexico, Lake Chapala. We use δ13C and δ15N stable isotope - based food web analyses to explore how they relate to other components of the Lake Chapala ecosystem. We find five Chirostoma species in top trophic levels of the Chapala food web compared to other fishes, relying on a combination of zooplankton, fish and benthic resources as energy sources. Food web metric analyses showed generally overlapping trophic niches for members of Chirostoma, especially in terms of δ13C. However, C. jordani had lower mean δ15N isotopic values than C. promelas. As a group, "pescados blancos" (C. sphyraena and C. promelas) also had higher δ15N signatures than "charales" (C. consocium, C. jordani and C. labarcae) reflecting greater piscivory, but these differences were not strong for all food web metrics used. Trophic overlap among species of Chirostoma in Lake Chapala raises questions about the forces that might have led to a morphologically diverse but functionally similar and monophyletic group of species.

Exploramos el papel trófico de un diverso grupo de peces (género Chirostoma) que habita en simpatría en el Lago Chapala, México central. Utilizamos isótopos estables de δ13C y δ15N para explorar la relación que guardan éstos peces con otros componentes del ecosistema. Encontramos a Chirostoma en niveles altos de la red trófica de Chapala, dependiendo energéticamente de zooplankton, peces y recursos del bentos. Análisis de parámetros de la red trófica demostraron traslape de nicho trófico para cinco miembros de Chirostoma, especialmente con relación a δ13C. Sin embargo, C. jordani tuvo un menor valor promedio de δ15N que C. promelas. Al ser analizados como grupo, los "pescados blancos" (C. sphyraena, C. promelas) tuvieron niveles promedio de δ15N mayores que los "charales" (C. consocium, C. jordani, C. labarcae), indicando mayor ictiofagia, pero las diferencias no fueron significativas para todos los parámetros de red trófica utilizados. El traslape trófico entre las especies de Chirostoma en Chapala da origen a cuestionamientos acerca de las fuerzas que pueden haber intervenido en el surgimiento de un morfológicamente diverso pero funcionalmente similar grupo monofilético de peces.

Isotopic traceability in body tissues and in different breeding periods of broilers / Rastreabilidade isotópica em tecidos corporais e em diferentes períodos de criação de frangos de corte

The inclusion of poultry viscera meal (VM) in broiler diets to possibly replace it with strictly vegetable diet (VE) and vice-versa, using the technique of carbon and nitrogen stable isotopes in different tissues was traced. One hundred ninety-two one-day-old chicks that had been distributed randomly were used in twelve experimental treatments with four replications of four chicks each. The treatments consisted of vegetable diet (VG) for diets containing FV going after a certain age or the reverse, in which the birds began feeding VM on diet and then switched to VE diet. At 42 days of age, samples of pectoral muscle (Pectoralis major), keel and tibia were collected, with later determination of isotopic ratios (13C/12C and 15N/14N). The stable isotopes technique couldn't trace the use of VM in feeding broilers when this ingredient was part of broiler diets only in the first seven, 14 or 21 days of age. However, this technique can be applied to younger poultry that have been sampled before a possible change in diet, since they can have the isotopic signature of feeding stabilized around two weeks of age.

Rastrearam-se a inclusão de farinha de vísceras de aves (FV) em dietas de frangos por ocasião de eventual substituição de dieta contendo FV por dieta estritamente vegetal, e vice-versa, por isótopos estáveis de carbono e de nitrogênio. Foram distribuídos aleatoriamente 192 pintos de um dia de idade, em 12 tratamentos com quatro repetições de quatro aves. Os tratamentos constituíam-se de dieta de vegetais (VG) passando para dietas contendo FV, após certa idade, ou o inverso, em que as aves começaram se alimentando de dieta FV e depois passaram para dieta VG. Aos 42 dias de idade, foram coletadas amostras de músculo peitoral (Pectoralis major), quilha e tíbia, para determinação das razões isotópicas (13C/12C e 15N/14N). A técnica dos isótopos estáveis somente não foi capaz de rastrear a utilização de FV na alimentação de frangos de corte, quando esse ingrediente fez parte da dieta das aves apenas nos primeiros sete, 14 ou 21 dias de idade. Entretanto, há a possibilidade da aplicação dessa técnica em aves mais jovens, amostradas antes de eventual mudança de dieta, pois elas podem ter a assinatura isotópica da alimentação estabilizada em torno de duas semanas de idade.

Water use in four model tropical plant associations established in the lowlands of Costa Rica

We examined soil water use patterns of four model plant associations established in the North Caribbean lowlands of Costa Rica by comparing the stable hydrogen isotope composition, δD, in xylem sap and in soil water at different depths, under rainy and dry conditions. Four 5-year-old model plant associations composed of 2 tree species (Hyeronima alchorneoides and Cedrela odorata) having different architecture and phenology were studied. Average tree height was 8.9 and 7.6 m, respectively. Each tree species was grown in monoculture and in polyculture with 2 perennial monocotyledons (Euterpe oleracea and Heliconia imbricata). Maximum rooting depth at the time of δD determination was ~ 2 m for almost all species. Most roots of all species were concentrated in the upper soil layers. Stomatal conductance to water vapor (gS) was higher in the deciduous C. odorata than in the evergreen H. alchorneoides; within each species, gS did not differ when the trees were grown in mono or in polyculture. During the rainy season, gradients in soil water δD were not observed. Average rainy season xylem sap δD did not differ among members of the plant combinations tested (-30 ‰), and was more similar to δD values of shallow soil water. Under dry conditions, volumetric soil water content declined from 50 to ~ 35%, and modest gradients in soil water δD were observed. xylem sap δD obtained during dry conditions was significantly lower than rainy season values. xylem sap δD of plants growing in the four associations varied between -9 and -22‰, indicating that shallow water was predominantly absorbed during the dry period too. Differences in xylem sap δD of trees and monocots were also detected, but no significant patterns emerged. The results suggest that: a) the plant associations examined extracted water predominantly from shallow soil layers (<1 m), b) the natural isotopic variation in soil and plant water at the study site was low, and c) the plant mixes obtain water from more than a single soil layer simultaneously. Temporal factors were important in determining the competition and complementary relations observed among the trees and the perennial monocots. Under the prevailing environmental conditions, water use in these plant associations was determined largely by species-specific attributes such as biomass allocation to fine roots, phenology, and canopy architecture, and to a lesser extent by water limitations. Rev. Biol. Trop. 56 (4): 1947-1957. Epub 2008 December 12.

Examinamos los patrones de uso de agua del suelo de cuatro asociaciones vegetales establecidas en el Caribe norte de Costa Rica, comparando la composición isotópica del hidrógeno, δD, en la savia del xilema y en el agua del suelo en condiciones lluviosas y secas. Estudiamos cuatro asociaciones de cinco años de edad compuestas por dos árboles (Hyeronima alchorneoides y Cedrela odorata) con diferente arquitectura y fenología, cultivados en mono y policultivo con dos monocotiledóneas perennes (Euterpe oleracea y Heliconia imbricata). Las excavaciones mostraron que la profundidad máxima de las raíces fue de 2 m para casi todas las especies, y que la mayor densidad de raíces se encontraba en la superficie del suelo. La conductividad estomática (gS) fue mayor en el árbol caducifolio (C. odorata) que en el perennifolio (H. alchorneoides); dentro de cada especie, gS no difirió cuando los árboles fueron cultivados en mono o en policultivo. Los resultados sugieren que: a) las asociaciones examinadas extrajeron agua predominantemente de las capas superficiales del suelo (<1 m), b) la variación natural en el acceso al agua del suelo por parte de las especies, y en las propiedades del suelo, fue baja, y c) las combinaciones de plantas obtuvieron agua de varias capas del perfil del suelo simultáneamente. Los factores relacionados con el tiempo fueron importantes en la determinación de las relaciones de competencia y complementariedad observadas entre los árboles y las monocotiledóneas perennes. En las condiciones ambientales prevalecientes, el uso del agua por parte de estas asociaciones de plantas fue determinado más por atributos, como la asignación de biomasa a las raíces finas, la fenología, y las propiedades del dosel, que por limitaciones en la disponibilidad de agua.

Application of isotope-selective non-dispersive infrared spectrometry for the evaluation of the 13C-urea breath test: comparison with three concordant methods

The aim of this work was to compare the performance of isotope-selective non-dispersive infrared spectrometry (IRIS) for the 13C-urea breath test with the combination of the 14C-urea breath test (14C-UBT), urease test and histologic examination for the diagnosis of H. pylori (HP) infection. Fifty-three duodenal ulcer patients were studied. All patients were submitted to gastroscopy to detect HP by the urease test, histologic examination and 14C-UBT. To be included in the study the results of the 3 tests had to be concordant. Within one month after admission to the study the patients were submitted to IRIS with breath samples collected before and 30 min after the ingestion of 75 mg 13C-urea dissolved in 200 ml of orange juice. The samples were mailed and analyzed 11.5 (4-21) days after collection. Data were analyzed statistically by the chi-square and Mann-Whitney test and by the Spearman correlation coefficient. Twenty-six patients were HP positive and 27 negative. There was 100 per cent agreement between the IRIS results and the HP status determined by the other three methods. Using a cutoff value of delta-over-baseline (DOB) above 4.0 the IRIS showed a mean value of 19.38 (minimum = 4.2, maximum = 41.3, SD = 10.9) for HP-positive patients and a mean value of 0.88 (minimum = 0.10, maximum = 2.5, SD = 0.71) for negative patients. Using a cutoff value corresponding to 0.800 per cent CO2/weight (kg), the 14C-UBT showed a mean value of 2.78 (minimum = 0.89, maximum = 5.22, SD = 1.18) in HP-positive patients. HP-negative patients showed a mean value of 0.37 (minimum = 0.13, maximum = 0.77, SD = 0.17). IRIS is a low-cost, easy to manage, highly sensitive and specific test for H. pylori detection. Storing and mailing the samples did not interfere with the performance of the test.