RESUMEN Empleando metodologías estandarizadas se estudiaron 30 cuerpos de agua en la Faja Volcánica Transmexicana a lo largo de un gradiente altitudinal (737 a 4283 msnm) y climatológico. Los lagos se incluyen en tres categorías: tectónicos (4), volcánicos (11 cráteres o maars, 7 represas volcánicas) y presas (8).]. In thirteen lakes, nutrient levels could be limiting primary productivity, mostly P, but also N and Si. Half of the lakes (16) were eutrophic or hypertrophic and most of these were also shallow (< 8 m) and correlated with warm, moist conditions. Ninety-seven taxa of aquatic organisms (phytoplankton, and surface sediment diatoms, testate amoebae, cladoceran and ostracodes) were reported, which could potentially be used as bioindicators. Principal component analysis (PCA) showed that temperature and precipitation were the main environmental gradients related to the lakes' limnological characteristics: colder climates related with lowest TDS (< 100 mg/L); dry climates with subsaline and hyposaline lakes, and warm-moist climates with eutrophic and hypertrophic lakes. Through the Procrustes technique we obtained indications that general geographic variables were important for some of the lakes, whereas the local factors were significant for others. It is through the knowledge of the basic limnology and biodiversity of Mexican lakes that more complex or detailed studies can be proposed leading to a better understanding, management, and conservation of water resources.

Abstract:Testate 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.

The ecology of aquatic protists such as testate amoebae is poorly known worldwide, but is almost completely unknown in lakes of the northern Neotropics. To address this knowledge gap, we analyzed testate amoebae (Amoebozoa: Arcellinidae) in lakes of the Lacandón Forest, one of the most biodiverse parts of southern México. We set out to evaluate the diversity of testate amoebae communities and assess whether testate amoebae taxa are reliable indicators of environmental variables dissolved oxygen and water depth. We collected 17 surface sediment samples from a range of water depths in six lakes across the Naha-Metzabok Biosphere Reserve, northeastern Chiapas state. We identified 15 testate amoebae taxa distributed across seven genera. Eleven were identified to species level and four to strain (infra-subspecific level), and taxa were distributed unevenly among samples. Distribution of taxa in samples was related to dissolved oxygen (DO) concentration in the water measured near the sediment surface. Arcella discoides and Centropyxis aculeata strain “aculeata” were the most tolerant of low oxygen concentrations, whereas the other taxa require higher DO levels. The influence of oxygen was also seen at the assemblage level. Sites with low DO concentrations had Shannon Diversity Index (SDI) values <1.5, an indication of stressful ambient conditions. We identified two species assemblage types, which are distinguished by their oxygen concentration requirements. Assemblage 1 was more diverse and possessed species that are intolerant of low oxygen concentrations, whereas Assemblage 2 possessed fewer, rarer, opportunistic species that tolerate stressful conditions. Low oxygen concentrations are related to water depth and the combination of these two variables is important in determining the composition of testate amoebae assemblages in Lacandón Forest lakes. Quantitative relationships between testate amoebae assemblages and water depth will enable use of sedimented amoebae remains for paleolimnological inference of past water level changes in lakes of the Lacandón Forest.

Protozoa are important members of ecosystems, but protozoa that inhabit caves are poorly known worldwide. In this work, we present data on the record and distribution of thirteen protozoa species in four underground biotopes (water, soil, bat guano, and moss), at Cueva de Los Riscos. The samples were taken in six different months over more than a year. Protozoa species were ciliates (eight species), flagellates (three species), amoeboid (one species), and heliozoan (one species). Five of these species are reported for the first time inside cave systems anywhere, and an additional three species are new records for Mexican caves. Colpoda was the ciliate genera found in all cave zones sampled, and it inhabited the four biotopes together with Vorticella. The biotopes with the highest specific richness were the moss, sampled near the main cave entrance, and the temporary or permanent water bodies, with ten species each. The greatest number of species was observed in April 2006 (dry season). With the exception of water, all biotopes are studied for the first time.

Testate amoebae are unicellular organisms characterized by a shell-like test. Due to their potential use as bioindicators (and paleoindicators), these organisms have been increasingly studied in the last decade, particularly in temperate latitudes. This study's objective was two-fold: to identify the testate amoeba communities sampled from 29 water bodies in Mexico and to determine if their presence and distribution also made them suitable bioindicators for tropical latitudes. A total of 40 taxa were recorded within 12 genera, and six significant variables -oxygen, pH, depth, temperature, conductivity, and total alkalinity -that explained testate amoeba distribution within and among the water bodies were identified through a canonical correspondence analysis. The Q-mode clusters rendered five assemblages, each named after their respective dominant species: 1) Centropyxis aculeata strain "aculeata" assemblage, 2) Difflugia oblonga strain "bryophila" assemblage, 3) diverse assemblage, 4) Cucurbitella tricuspis assemblage, and 5) Difflugia protaeiformis strain "acuminata" assemblage. We found that Cucurbitella tricuspis and the Difflugia protaeiformis strain "acuminata" have similar ecological preferences to those reported previously for temperate lakes, with the former identified as an indicator of eutrophic environments and the latter as an indicator of low oxygen levels. On the other hand, Centropyxis aculeata strain "aculeata" and Arcella vulgaris seem to indicate adverse conditions, but the source of this environmental stress apparently differs from that reported in temperate latitudes. Although this stress source could not be identified in all cases, our study nonetheless demonstrates that testate amoebae in the water bodies of central Mexico could reveal the presence of environmental stress.