RESUMO
AbstractTestate amoebae are common single-celled eukaryotic organisms in aquatic ecosystems. Despite their important role in these ecosystems, and their potential as bioindicators and paleoindicators, they remain poorly studied in Mexico. The major objectives of this study were to: 1) increase knowledge of testate amoebae in Mexico's tropical lakes, and 2) create a catalog of high-quality scanning electron micrographs that can be used for future ecological and paleoenvironmental studies. We collected surface-sediment samples from 29 lakes, located in the Transmexican Volcanic Belt, one at each lake during June and October 2011, and March 2013. Sediments were collected with an Ekman grab and preserved in anhydrous ethanol. Sub-samples were observed under a stereomicroscope and morphometric data for each species were recorded. Total diameter and aperture diameter were measured on circular tests. Irregularly shaped tests were measured for length and width of the aperture and for the size of the whole test. If a specimen possessed spines, the length of one randomly selected spine was measured. The best-preserved specimen of each taxon was photographed with an optical microscope and a scanning electron microscope (SEM). We found 41 taxa of testate amoebae belonging to the genera: Arcella, Argynnia, Centropyxis, Cucurbitella, Cyclopyxis, Cyphoderia, Difflugia, Euglypha, Lesquereusia, Pentagonia, Pseudodifflugia and Scutiglypha. Twelve species not previously reported for Mexico were recorded, along with 13 varieties. The average number of taxa recorded in each lake was eight, and the highest taxonomic richness was 18. The taxon found in the greatest number of lakes was Centropyxis aculeata var. aculeata. Taxonomic richness varied among lakes in the same region. This could reflect lake-specific differences in environmental conditions, underscoring the need for more detailed studies that include collection of data on physical and chemical variables in the lakes. Our results highlighted the need of further studies for the distribution patterns and ecology of lacustrine testate amoebae. Rev. Biol. Trop. 64 (1): 377-397. Epub 2016 March 01.
ResumenLas amebas testadas son organismos eucariontes unicelulares frecuentes en ecosistemas acuáticos. A pesar de su importante rol en estos ecosistemas, y su potencial como bioindicadores y paleoindicadores, son poco estudiados en México. Los principales objetivos de este estudio fueron: 1) incrementar el conocimiento de las amebas testadas en lagos tropicales de México y 2) crear un catálogo de microfotografías electrónicas de barrido de alta calidad que pueda ser usado en futuros estudios ecológicos y paleoambientales. Recolectamos muestras de sedimentos superficiales de 29 lagos, ubicados en la Faja Volcánica Transmexicana, una vez en cada lago durante junio y octubre 2011 y marzo 2013. Los sedimentos se recolectaron con una draga tipo Ekman y se preservaron en etanol anhidro. Las sub-muestras se observaron al microscopio estereoscópico. Para cada especie fueron registrados sus datos morfométricos. En testas circulares fueron medidos el diámetro y la apertura total. En testas irregulares fueron medidos el largo y ancho de la apertura y el tamaño de toda la testa. Si un ejemplar poseía espinas, se seleccionó una al azar y se midió su longitud. El ejemplar mejor preservado de cada taxón fue fotografiado con un microscopio óptico y en microscopio electrónico de barrido (MEB). Encontramos 41 taxa de amebas testadas pertenecientes a los géneros Arcella, Argynnia, Centropyxis, Cucurbitella, Cyclopyxis, Cyphoderia, Difflugia, Euglypha, Lesquereusia, Pentagonia, Pseudodifflugia y Scutiglypha. Se registraron 12 especies y 13 variedades que no estaban reportadas previamente en México. El número promedio de taxa registrados en cada lago fue de ocho, y la riqueza taxonómica mayor fue de 18. El taxón encontrado en el mayor número de lagos fue Centropyxis aculeata var. aculeata. La riqueza taxonómica compartida por lagos de la misma región no fue muy similar. Esto puede reflejar diferencias en las condiciones ambientales, evidenciando la necesidad de elaborar estudios más detallados que incluyan la recolección de datos de las variables físico-químicas en los lagos. Nuestros resultados resaltan la necesidad de estudios posteriores acerca de los patrones de distribución y la ecología de las amebas testadas lacustres.
Assuntos
Biodiversidade , Amoeba/classificação , Amoeba/ultraestrutura , Clima Tropical , Lagos , MéxicoRESUMO
In the present study Aspidoras fuscoguttatus Nijssen & Isbrücker, 1976 diet was investigated based on specimens from 18 streams of São Paulo State northwestern region, upper Rio Paraná system. Stomach contents of 246 specimens were analyzed, with the registration of 26 types of feeding items showing high predominance of the autochthonous ones. Of these, Chironomidae, Simuliidae, and Ceratopogonidae aquatic larvae were the most important items, but the contribution of detritus, testate amoebas, and vegetal debris changed according to streams features. Whereas in clear waters feeding items can be visually selected by fishes, in turbid waters this selection may not occur. Thus, the species' ability in taking resources in sandy streams with turbid waters and the abundance of resources (Chironomidae larvae) are factors that seem to explain its high abundance and broad occurrence in the region.
Assuntos
Fauna Aquática , Comportamento Alimentar/classificação , Água Doce , Ecossistema/análise , Ecossistema/efeitos adversos , Peixes/anatomia & histologia , Peixes/classificaçãoRESUMO
The present study aimed to analyze the species richness of testate amoebae, as well as to describe their geographic distribution and different habitat types in Brazilian freshwater environments. Until now, 346 infrageneric taxa have been recorded, belonging to 13 families and 40 genera. In the Center-West region, 267 taxa were recorded; 188 taxa in the Southeast; 129 taxa in the South, 53 taxa in the North; and 18 taxa in Northeast region. A total of 282 taxa were recorded in plankton; 80 taxa in aquatic macrophytes; 81 taxa in sediment; and 73 taxa in moss/sphagnum. The results regarding testate amoebae species richness are not yet conclusive, given that most research on these organisms was carried out in central, southeastern and southern Brazil. The higher number of taxa observed in plankton may be due to the fact that most studies on testate amoebae in Brazil had been carried out in the planktonic compartment, including reservoirs, floodplain lagoons, channels, tributaries and rivers. In addition, the majority of studies with sediment samples were conducted in estuaries or coastal lagoons, where salinity is a restricting factor for the occurrence of these organisms.
Este trabalho visa realizar um levantamento da riqueza de espécies de amebas testáceas, bem como descrever a distribuição geográfica e a distribuição em diferentes tipos de habitats desses organismos em ambientes aquáticos continentais brasileiros. Até o momento, são registrados 346 táxons infragenéricos, pertencentes a 13 famílias e 40 gêneros. São registrados 267 táxons na região centro-oeste, 188 táxons na região sudeste, 129 táxons na região sul, 53 táxons na região norte e 18 táxons na região nordeste. São registrados 282 táxons no plâncton; 131 táxons em macrófitas aquáticas, 81 táxons no sedimento e 73 táxons em musgos/esfágnos. Os resultados sobre a riqueza de tecamebas não é ainda conclusiva, visto que a maioria das pesquisas foi conduzida nas regiões centro-oeste, sudeste e sul. O maior número de táxons registrados no plâncton pode ser em virtude de que a maioria dos estudos sobre tecamebas, no Brasil, ter sido realizada no compartimento planctônico, incluindo reservatórios, lagoas de várzeas, canais, tributários e rios. Além disso, a maior parte dos estudos, em amostras de sedimento, foi conduzida em estuários ou lagoas costeiras, onde a salinidade é um fator limitante para a ocorrência desses organismos.