Aspectos ecológicos, taxonómicos y de distribución de cianobacterias bentónicas en ríos de la región central de México

Resumen:Antecedentes y Objetivos: Las cianobacterias son algas procariontes oxifotótrofas presentes en gran variedad de hábitats y son componentes importantes de las comunidades bentónicas en muchos ambientes continentales y marinos. En México su diversidad en ríos es poco conocida; por ello, este estudio contribuye al conocimiento ficoflorístico en cinco ríos de la región central de México. Se incluyen descripciones e ilustraciones, estimaciones de su diversidad, un análisis de las relaciones entre formas de crecimiento y factores microambientales, y se discute la validez de su caracterización morfológica y ecológica en la delimitación de las especies encontradas.Métodos: Se realizaron muestreos en secas y lluvias en dos ríos silíceos y tres ríos calcáreos del centro de México. Se registró la temperatura del agua, conductividad específica y pH, se analizaron iones mayores (Ca2+, Mg2+, K+, Na+, Si-SiO2, HCO3-, Cl-, SO43-) y nutrientes (NH4+,NO2-, NO32-, PO43-), se estimó la diversidad de las cianobacterias registradas con el índice de Shannon-Weaver y se describieron sus hábitats y microhábitats. La identificación taxonómica se realizó utilizando literatura especializada.Resultados clave: Se identificaron cuatro asociaciones y nueve especies pertenecientes a tres órdenes, siete familias y siete géneros. Se distinguieron dos grupos: el formado por Nostoc parmelioides-Coleodesmium wrangelii y Phormidium lividum-Leptolyngbya truncata en ríos silíceos de montaña y el compuesto por Schizothrix mexicana-Phormidium subfuscum, Homoeothrix juliana-Heteroleibleinia fontana y Nostoc verrucosum en ríos calcáreos cálidos. Se reconocieron dos patrones de distribución ecológica: 1) las especies del orden Nostocales presentes en condiciones estresantes de luz y velocidad de corriente y 2) los taxa de los órdenes Oscillatoriales y Synechococcales registrados en sitios con valores promedio de luz y flujo de agua.Conclusiones: La caracterización morfológica y ecológica de especies de cianobacterias contribuye a su conocimiento ficoflorístico y es la base para futuras investigaciones sobre taxonomía, sistemática y uso sustentable de recursos algales.Palabras clave: asociaciones, diversidad, ríos calcáreos, ríos silíceos. Abstract:Background and Aims: Cyanobacteria are oxyphototrophic prokariotic algae present in great variety of habitats and they are important components of the benthic communities in many continental and marine environments. In Mexico, their diversity in streams is less known; therefore, this study contributes to phycofloristic knowledge in five streams of the central region of Mexico. Descriptions and illustrations, estimations of their diversity, an analysis of the relationships between growth forms and microenvironmental factors are included, and the validity of their morphological and ecological characterization in the delimitation of the species found is discussed.Methods: Sampling was carried out in dry and rainy seasons in two siliceous streams and three calcareous streams of central Mexico. Water temperature, specific conductivity and pH were recorded, major ions (Ca2+, Mg2+, K+, Na+, Si-SiO2, HCO3-,Cl-, SO43-) and nutrients (NH4+,NO2-, NO32-, PO43-) were analyzed, the diversity was estimated of the cyanobacteria registered with the Shannon-Weaver index, and their habitats and microhabitats were described. Taxonomic identification was carried out with specialized literature.Key results: Four associations and nine species belonging to three orders, seven families and seven genera were identified. Two groups were distinguished: one formed by Nostoc parmelioides-Coleodesmium wrangelii, Phormidium lividum-Leptolyngbya truncata in siliceous and mountain streams, and one composed by Schizothrix mexicana-Phormidium subfuscum, Homoeothrix juliana-Heteroleibleinia fontana and Nostoc verrucosum in calcareous, warm streams. Two ecological distribution patterns were recognized: 1) the Nostocales species present in stressful conditions of light and current velocity and 2) the taxa of Oscillatoriales and Synechoccales registered in sites with mean values of light and water flow.Conclusions: Morphological and ecological characterization of cyanobacterial species contributes to their phycofloristic knowledge and the base for future research on taxonomy, systematics and sustainable use of algal resources.Key words: associations, calcareous streams, diversity, siliceous streams.

New species of Hemerodromia Meigen (Diptera: Empididae: Hemerodromiinae) associated with limestone karstic waters in Thailand

Species descriptions are provided for five new species of Hemerodromia (H. aliaextriata sp. nov., H. deprimatura sp. nov., H. oretenebraea sp. nov., H. pairoti sp. nov. H. samoha sp. nov.). The new species have an apparently obligate association with calcareous streams, rivers and tufa formations in limestone karst landforms in Thailand. Hemerodromia menghaiensis Yang & Yang is here reported for the first time in Thailand.

Immunolocalisation of microcystins in colonies of the cyanobacterium Rivularia in calcareous streams

The cyanobacterium Rivularia is often the dominant genus in unpolluted stretches of many calcareous streams. Previous studies have detected microcystins in field-collected colonies from Mediterranean streams in Spain. Because sheaths and mucilage represent a substantial part of the colonies, the localisation of microcystins within Rivularia colonies was tested with immunological methods to elucidate the role of mucilage in toxicity. Microcystins were localised inside the trichomes, in the filament sheaths and in the colonial mucilage. The presence of microcystins was also shown in some heterocysts, but no mircocystins were detected in multicellular hairs. We suggest that microcystins are important for a benthic organism growing slowly for much of the time, that some labour division may exists between the cells in the colony and that these immunological methods may be a useful alternative for microcystin detection.