Javier Carmona

Temporal and spatial distribution of macroalgal communities of mountain streams in Valle de Bravo Basin, central Mexico

The stream macroalgal community is controlled by heterogeneous physical, chemical, and biological factors related with multiple spatial and temporal scales; however, the mechanisms that explain diversity and distribution are scarcely known. The present investigation was conducted to characterize the macroalgal community structure and spatial and temporal distribution and to recognize biogeographic affinities with mountain streams from other regions. Habitat characteristics, abundance, and diversity were investigated in four mountain streams of Valle de Bravo Basin, central Mexico, during two annual cycles. Sampling of visible benthic growths was collected in the most contrasting parts of the year. Physicochemical parameters were recorded in situ at each site and the main ions and nutriments were evaluated for every collection. Statistical analysis between dates was assessed with one-way analysis of variance (ANOVA) and Canonical Correspondence Analysis (CCA). Observed richness average was four species per site and the high abundance of Phormidium interruptum, Nostoc parmelioides, Paralemanea mexicana, Batrachospermum gelatinosum, Sirodotia suecica, Cladophora glomerata, and Prasiola mexicana correlated with cold dry season, high current velocity, and a major size substrate. Valle de Bravo streams can be viewed as a habitat subjected to moderated disturbance, mainly due to the effects of seasonal changes in rainfall contrary to torrents expected of tropical regions. The seasonal patterns of macroalgal communities in Valle de Bravo basin were typically characterized by two distinct periods essentially determined by the rainfall regime and related to temperature, and can be viewed as habitats subjected to moderate disturbance according to intermediate disturbance hypothesis. The distribution species pattern registered suggests a group of temperate species frequently found in mountain regions of the Mexican Volcanic Belt and temperate eastern region of North America and may indicate a possible biogeographic connection with the Neartic region with similar environmental requirements.

Phenotypic and genotypic characteristics of Phormidium-like cyanobacteria inhabiting microbial mats are correlated with the trophic status of running waters

Polyphasic analysis was carried out of natural samples and strains isolated from Phormidium mats, collected from different Spanish rivers with distinct water quality. 16S rRNA gene analysis separated five main clusters in a phylogenetic tree corresponding to five main, previously observed morphotypes. Two isolated strains and three natural samples had a relatively homogeneous morphology, which could correspond to Phormidium autumnale, and their sequences grouped in a well-supported cluster (morphotype–genotype I). However, ultrastructural differences were found among representatives from this cluster, and three clades could be separated in a further phylogenetic analysis. The samples belonging to the first clade were characteristic of hypertrophic waters, while representatives of the second grew in mesotrophic conditions, and those of the third in eutrophic waters. These results suggested that our representatives of morphotype–genotype I belong to three different species. According to our results and other published data, complementary information was obtained on the basis of morphological, phylogenetic and ecological criteria. Morphotype–genotype II, corresponding to Phormidium terebriforme, is a potential indicator of polluted waters. Oscillatoria tenuis, corresponding to morphotype–genotype III, is characteristic of eutrophic conditions. Phormidium mats identified as Phormidium corium (morphotype–genotype IV) were found to be characteristic of waters with low nutrient levels. Finally, morphotype–genotype V, identified as Phormidium aerugineo-caeruleum was dominant in oligo- to mesotrophic conditions.

Systematics and distribution of Thorea (Thoreaceae, Rhodophyta) from central Mexico and south-eastern Brazil

Thirteen populations of Thorea were analyzed from central Mexico and south‐eastern Brazil. All populations were considered as belonging to a single species [Thorea hispida (Thore) Desvaux], with wide variation of morphological features. Secondary branches varying in frequency were observed in several populations with an overlapping in the range of branch density for Thorea violacea Bory and T hispida (0–9 and 11–41 per 30 mm, respectively). As this is the most distinguishing character and on the basis of the overlapping (within a same population or even a single plant), we regarded T. violacea as a synonym of T hispida.‘Chantransia’ stage in culture, as well as gametophyte and carposporophyte were described in detail. We confirmed tine coexistence of asexual monosporangia with sexual reproductive structures (carpogonia and spermatangia) and carposporangia. Size, content, arrangement and chromosome number were the most distinctive characteristics among spermatangia, carposporangia and monosporangia. Monosporangia can be promptly differentiated from spermatangia by their granulated content and larger size but they are similar to carposporangia in shape and size; however, monosporangia are not arranged in fascicles. Structures resembling bisporangia were observed in female plants of some populations. Chromosome numbers were n = 4 for spermatangia and fascicle cells, and 2n ca 8 for gonimoblast filaments, carpospores and the ‘Chantransia’ stage cells. The populations of Thorea from central Mexico and south‐eastern Brazil corroborated the known world distribution for T. hispida, consisting dommantly of tropical to subtropical rainforests, sometimes extending into warm temperate areas. Thorea hispida occurred in warm (temperature 17.6–28.O°C), neutral to alkaline (pH 7.0–8.0), high ion content (specific conductance 59–2140 μS cm−1), moderate flowing (current velocity 17–43 cm/s) and shallow waters (depth <50cm); these data are essentially similar to previous reports.

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.

Species richness and diversity of benthic diatom communities in tropical mountain streams of Mexico

Abstract We examined community structure of benthic diatoms and their substratum preferences (epilithic vs. macroalgae) by season in 4 tropical mountain streams in central Mexico. Of the 74 species compiled, Cymbella silesiaca, Rhoicosphenia abbreviate, and Reimeria sinuata were the most abundant and frequent. About 14% of species were exclusively epilithic, 13% were associated with macroalgae, and 73% had no clear preference. Environmental factors most closely related to spatial and temporal distribution of epilithic diatoms were changes in stream discharge and water temperature. For diatoms associated with macroalgae, the most important factors were changes in current velocity and the coverage and richness of macroalgae. The similarities in species richness and diversity in the 4 study sites suggest that the diatom community develops under conditions of moderate disturbance. The few differences found in species richness between epilithic and macroalgae-associated diatoms suggest that these diatoms do not have substratum preferences. The abundance of macroalgae-associated diatoms in all sites suggests a positive effect (facilitation) of macroalgae on diatoms.

Phenology of Sirodotia suecica (Batrachospermaceae, Rhodophyta) in a high-altitude stream in central Mexico

The morphology and phenology of a monoecious population of Sirodotia suecica Kylin was evaluated seasonally in a central Mexican fifth‐order high‐altitude stream. Abundance of gametophytes is positively correlated with concentrations of total dissolved solids, specific conductivity and total ionic concentration; being present the whole dry season and disappearing in the rainy season. The gametophytes grew in eutrophic circumstances and particular microhabitat conditions: high current velocity (66–122 cm s−1), low irradiance (75–263 µmol photons m−2 s−1) and shallow depth (7–26 cm). Percent cover of gametophytes ranged from 5–90% and significant differences in abundance were not observed when alga was present. Some morphological and reproductive characteristics seem to be adaptations to high current velocity: abundant secondary branches, spermatangia and carpogonia. ‘Chantransia’ stage, microscopic creeping filaments associated with the base of the gametophyte, were not observed in natural conditions. In terms of reproductive success, the population studied can be regarded as highly efficient, considering the high fertilized carpogonia rate, similar to monoecious populations in lotic habitats. However S. suecica was not common in the study region because it was restricted to particular microhabitat conditions.

Epilithic diatom communities of selected streams from the Lerma-Chapala Basin, Central Mexico, with the description of two new species

Abstract The Lerma-Chapala Basin, in Central Mexico, is geologically heterogeneous, climatically diverse and boasts high biodiversity, lying within two Biodiversity Hotspots, namely Mesoamerica and the Madrean Pine–Oak Woodlands. Epilithon and water samples were collected in the basin from 14 sampling sites three times each, two sampling campaigns during the rainy season and one in the dry season. A total of 274 infrageneric taxa in 48 genera were recorded. The taxonomic composition observed was dominated by taxa from the genera Nitzschia, Gomphonema, Pinnularia, Navicula, Sellaphora and Eunotia. About a third of the taxa found could not be identified to the species level. From those unidentified morphodemes, two are described as new species, namely Brachysira altepetlensis and Sellaphora queretana. Furthermore, Eolimna rhombica is transferred to Sellaphora. Canonical Correspondence Analysis (CCA) revealed that specific conductivity and pH were the main environmental factors driving the community composition observed. Three groups of samples were identified after the CCA: 1) characterized by acidic waters and low conductivity; 2) with circumneutral waters, low specific conductivity and high temperature and phosphorous concentrations; and 3) characterized by circumneutral waters, high conductivity and low nitrogen concentrations. The indicator value method (IndVal), based on the relative abundance and relative frequency of the most abundant taxa was calculated based on the groups observed in the CCA, identifying the characteristic taxa for each of the three groups.