Chroakolemma gen. nov. (Leptolyngbyaceae, Cyanobacteria) from soil biocrusts in the semi-desert Central Region of Mexico

Twelve strains of Leptolyngbya-like filaments were isolated from biological soil crust samples from two localities in the Central Region of Mexico. The strains were morphologically distinguished from most Synechococcalean species by the obligate presence of a blackish sheath. Phylogenetic analysis based on 16S rRNA gene sequence placed all strains into a strongly supported single clade sister to Scytolyngbya. The genetic identity between our strains and all other Synechococcales, including Scytolyngbya, was less than 95%, and the strains were further distinguished by morphology and terrestrial ecology. The conserved domains of the 16S-23S ITS region had secondary structures distinct from all other closely related genera, which included Scytolyngbya, Stenomitos, Chamaethrix, and Pantanalinema. Based on the combination of morphological, molecular, and ecological evidence, we here describe two species: Chroakolemma opaca gen. et sp. nov. and C. pellucida gen. et sp. nov. Based on the ability to form blackish sheaths, these two species are morphologically similar to Leptolyngbya edaphica, Chamaethrix vaginata and Trichocoleus badius. The latter two species have been sequenced and are phylogenetically distant from Chroakolemma. Leptolyngbya edaphica is a soil species described from Russia and shares other morphological similarities with Chroakolemma, including wide sheaths, coiled filaments, pale blue-green trichomes, and constricted crosswalls. We consider these characteristics diagnostic of Chroakolemma, and accordingly propose Chroakolemma edaphica comb. no

Chroakolemma gen. nov. (Leptolyngbyaceae, Cyanobacteria) from soil biocrusts in the semi-desert Central Region of Mexico

Twelve strains of Leptolyngbya-like filaments were isolated from biological soil crust samples from two localities in the Central Region of Mexico. The strains were morphologically distinguished from most Synechococcalean species by the obligate presence of a blackish sheath. Phylogenetic analysis based on 16S rRNA gene sequence placed all strains into a strongly supported single clade sister to Scytolyngbya. The genetic identity between our strains and all other Synechococcales, including Scytolyngbya, was less than 95%, and the strains were further distinguished by morphology and terrestrial ecology. The conserved domains of the 16S-23S ITS region had secondary structures distinct from all other closely related genera, which included Scytolyngbya, Stenomitos, Chamaethrix, and Pantanalinema. Based on the combination of morphological, molecular, and ecological evidence, we here describe two species: Chroakolemma opaca gen. et sp. nov. and C. pellucida gen. et sp. nov. Based on the ability to form blackish sheaths, these two species are morphologically similar to Leptolyngbya edaphica, Chamaethrix vaginata and Trichocoleus badius. The latter two species have been sequenced and are phylogenetically distant from Chroakolemma. Leptolyngbya edaphica is a soil species described from Russia and shares other morphological similarities with Chroakolemma, including wide sheaths, coiled filaments, pale blue-green trichomes, and constricted cross- walls. We consider these characteristics diagnostic of Chroakolemma, and accordingly propose Chroakolemma edaphica comb. nov

Estimación de erosión de suelos utilizando sensores remotos y programación genética

Los índices de vegetación (IVs) son ampliamente utilizados para extraer información de la vegetación a partir de imágenes satelitales. Los modelos de erosión, como la "Ecuación Universal Revisada de la Pérdida de Suelo" (RUSLE) usan IVs como insumo para estimar el factor de cobertura vegetal (C). El factor C es uno de los más importantes porque cuantifica la cobertura que actúa como capa protectora entre el suelo y los elementos atmosféricos. Sin embargo los IVs encontrados en el estado-delarte arrojan pobres resultados, ya que la mayoría de éstos están diseñados para detectar vegetación verde y no vegetación seca; la cual es también un importante factor que contribuye al desempeño del factor C. El propósito de esta investigación es desarrollar un método basado en programación genética para sintetizar IVs que estén mejor correlacionados con el factor C. Los resultados experimentales ilustran la eficiencia de este método y su efecto en el cálculo de erosión en una zona geográfica real. Los índices sintetizados obtienen una mejor aproximación al factor C obtenido en campo que cuando se utilizan los índices reportados en el estado-del-arte.Palabra(s) Clave(s): erosión por agua, índices de vegetación, programación genética, percepción remota, RUSLE

Taxonomía ay distribución de Hildenbrandia Nardo (Hildebrandiales, Rhodophyta) de agua dulce en la región central de México

This work includes a taxonomic analysis, habitat descriptions and distribution of 23 populations of the genus Hildenbrandia, collected in 14 sities in Mexico and one in Central Europe. Twenty two populations from Mexico were considered as belonging to a sigle species (H. angolensis), characterized by having small cell diameter (mean 4.1 µm). The second species (H. rivularis), represented by 1 population from central Europe was characterized by the large cell diameter (mean 6.4 µm). The presence of propagules was observed in 10 Mexican populations. Hildenbrandia angolensis tended to occur in warm (temperature 23-27 ºC), neutral to alkalline (pH 7.0-8.0), high ion content (specific conductance (700-1520 µS cm-1), moderate to fast flowing, high alkalinity (400-554 mg l-1) and shallow waters (depth typically <70 cm); these data are essntially similar to previous records. Hildenbrandia angolensis is described for the first time from the higher Balsas and lower Papaloapan basins, both ocurring mostly in areas of tropical or subtropical rainforests.En este trabajo se presentan los resultados del análisis taxonómico, descripción ambiental y la distribución de 23 poblacioes del género Hildenbrandia recolectadas en 14 localidades de México y una del centro de Europa. Se reconocieron dos grupos, el primero fue formado por todas las poblaciones mexicanas que se caracterizaron por el diámetro celular pequeño (promedio 4.1µm) y fueron consideradas como una sola especie (H. angolensi). La sgunda especies se diferenció por el diámetro celular mayor (promedio 6.4 µm) y correspondió a la población ueropea (H. rivularis). Se registraron propágulos vegetativos en 10 poblaciones mexicanas Hildenbrandia angolensis se presentó en ríos y manantiales con temperatura levada (23-27 ºC), neutral a alcalina (pH 7.0-8.0), alto contenido de iones (conductividad específica 700-1520 µS cm-1), velocidad de corriente de moderada a alta, alcalinidad alta (400-554 mg l-1) y sitios sombreados con poca profundidad (típicamente<70cm); estos datos fueron similares a los registros previos. Hildenbrandia angolensis es descrita por primera vez en la cuenca alta del río Balsas y cuenca baja del río Papaloapan, en áreas con clima tropical a subtropical

Ecology and morphological characterization of gametophyte and 'Chantransia' stages of Sirodotia huillensis (Batrachospermales, Rhodophyta) from a stream in central Mexico

The morphology and phenology of Sirodotia huillensis was evaluated seasonally in a central Mexican first-order calcareous stream. Water temperature was constant (24-25°C) and pH circumneutral to alkaline (6.7-7.9), and calcium and sulfates were the dominant ions. The gametophyte stages were characterized by the presence of a distinctive mucilaginous layer, a marked difference in phycocyanin to phycoerythrin ratio between female and male plants, and the presence of a carpogonia with a large trichogyne (>60 μm). Occasionally three capogonia were observed on a single basal cell. The 'Chantransia' stages were morphologically similar to those described for the other members of Batrachospermales. A remarkable observation was the formation of dome-shaped structures, consisting of prostrate filaments that are related with the development of new gametophytes. Chromosome numbers were n = 4 for fascicle cells, cortical filament cells and dome-shaped cells, and 2n = 8 for gonimoblast filament cells and 'Chantransia' stage filaments. Gametophytes and 'Chantransia' stages occurred in fast current velocities (60-170 cm/s) and shaded (33.1-121 μmol photons/m2/s) stream segments. The population fluctuated throughout the study period in terms of percentage cover and frequency: the 'Chantransia' stages were most abundant in the rainy season, whereas gametophytic plants had the highest frequency values during the dry season. These results were most likely a result of fluctuations in rainfall and related changes in current velocity. Some characteristics of this population can be viewed as probable adaptations to high current velocities: the mucilaginous layer around plants that reduces drag; potential increase in fertilization by the elongate and plentiful trichogynes and abundant dome-shaped structures producing several gametophytes