Geography is more important than life history in the recent diversification of the tiger salamander complex.

The North American tiger salamander species complex, including its best-known species, the Mexican axolotl, has long been a source of biological fascination. The complex exhibits a wide range of variation in developmental life history strategies, including populations and individuals that undergo metamorphosis; those able to forego metamorphosis and retain a larval, aquatic lifestyle (i.e., paedomorphosis); and those that do both. The evolution of a paedomorphic life history state is thought to lead to increased population genetic differentiation and ultimately reproductive isolation and speciation, but the degree to which it has shaped population- and species-level divergence is poorly understood. Using a large multilocus dataset from hundreds of samples across North America, we identified genetic clusters across the geographic range of the tiger salamander complex. These clusters often contain a mixture of paedomorphic and metamorphic taxa, indicating that geographic isolation has played a larger role in lineage divergence than paedomorphosis in this system. This conclusion is bolstered by geography-informed analyses indicating no effect of life history strategy on population genetic differentiation and by model-based population genetic analyses demonstrating gene flow between adjacent metamorphic and paedomorphic populations. This fine-scale genetic perspective on life history variation establishes a framework for understanding how plasticity, local adaptation, and gene flow contribute to lineage divergence. Many members of the tiger salamander complex are endangered, and the Mexican axolotl is an important model system in regenerative and biomedical research. Our results chart a course for more informed use of these taxa in experimental, ecological, and conservation research.

Olefin-Supported Cationic Copper Catalysts for Photochemical Synthesis of Structurally Complex Cyclobutanes.

The sole method available for the photocycloaddition of unconjugated aliphatic alkenes is the Cu-catalyzed Salomon-Kochi reaction. The [Cu(OTf)]2 ⋅benzene catalyst that has been standard in this reaction for many decades, however, is air-sensitive, prone to photodecomposition, and poorly reactive towards sterically bulky alkene substrates. Using bench-stable precursors, an improved catalyst system with superior reactivity and photostability has been designed, and it offers significantly expanded substrate scope. The utility of this new catalyst for the preparation of sterically crowded cyclobutane structures is highlighted through the preparation of the cores of the natural products sulcatine G and perforatol.

A Tale of Two Axolotls.

The Mexican axolotl (Ambystoma mexicanum) is an icon of culture, a revered aquarium pet, and a highly valued animal model in biomedical research. Unfortunately, Mexican axolotls are critically endangered in their natural Xochimilco habitat in Mexico City. If axolotls go extinct, current efforts to conserve the Xochimilico ecosystem will be undermined, as will efforts to genetically manage the laboratory populations that are needed to sustain research efforts around the world. A concerted global effort is needed to protect and manage this irreplaceable species in natural and laboratory environments.

Scientists raise alarms about fast tracking of transoceanic canal through Nicaragua.

Seeking economic growth and job creation to tackle the nation's extreme poverty, the Nicaraguan government awarded a concession to build an interoceanic canal and associated projects to a recently formed Hong Kong based company with no track record or related expertise. This concession was awarded without a bidding process and in advance of any feasibility, socio-economic or environmental impact assessments; construction has begun without this information. The 278 km long interoceanic canal project may result in significant environmental and social impairments. Of particular concern are damage to Lake Cocibolca, a unique freshwater tropical lake and Central America's main freshwater reservoir; damage to regional biodiversity and ecosystems; and socio-economic impacts. Concerned about the possibly irreparable damage to the environment and to native communities, conservationists and the scientific community at large are urging the Nicaraguan government to devise and reveal an action plan to address and mitigate the possible negative repercussions of this interoceanic canal and associated projects. Critical research needs for preparation of a comprehensive benefit-cost analysis for this megaproject are presented.

Antibiotic resistance of ESKAPE group-microorganisms in health institutions from Hermosillo and Ciudad Obregón, Sonora, México.

Introduction: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. are microorganisms referred as the ESKAPE group pathogens. These microorganisms have generated great concern in health institutions around the world since most of them have resistance to multiple antibiotics and cause most infections associated with healthcare, as well as community infections. The aim of this study was the analysis of antibiotic resistance in microorganisms of the ESKAPE group, recovered from clinical samples in 11 health institutions from Hermosillo and Ciudad Obregón in the State of Sonora, México, during the period from 2019 to 2020. Methods: A cross-sectional, descriptive, observational, and temporality epidemiological study was carried out. A comparative and statistical analysis of antibiotic resistance was carried out using the chi-square test, and small values were analyzed using Fisher's exact test p ≤ 0.05. Results and discussion: All the ESKAPE group microorganisms showed significant differences in antibiotic resistance percentages between both cities. High resistance percentages for some antibiotics, like cephalosporins and ciprofloxacin were detected for Klebsiella pneumoniae and Acinetobacter baumannii.

Pyogenic liver abscess caused by an atypical hypervirulent Klebsiella pneumoniae K1-ST23 in Mexico.

Hypervirulent K. pneumoniae infection has been raising worldwide and is one of the major causes of community-acquired pyogenic liver abscess. We described a case report of pyogenic liver abscess caused by an atypical hypervirulent (non-hypermucoviscous) K. pneumoniae K1 ST23 in a diabetic Asian patient who resided in Mexico. The susceptibility to antimicrobials, pathogenicity, molecular and genomic analysis were determined. A man from Guangdong (China) with a recent diagnosis of diabetes mellitus was admitted to the hospital, and he denied traveling in the last 3 months. A computed tomography revealed a right lobe liver abscess. On the third day after admission a Klebsiella pneumoniae isolate (14652) was obtained. The isolate corresponded to a susceptible K. pneumoniae with capsular type K1 and ST23 (CG23) and exhibited a non-hypermucoviscous phenotype. The isolate 14652 was genetically related to the globally distributed lineage ST23-KL1. This study describes the first case in Mexico of K. pneumoniae capsular type K1 and ST23 with an atypical hypervirulent phenotype.

Characterization of immunoglobulin loci in the gigantic genome of Ambystoma mexicanum.

Background: The axolotl, Ambystoma mexicanum is a unique biological model for complete tissue regeneration. Is a neotenic endangered species and is highly susceptible to environmental stress, including infectious disease. In contrast to other amphibians, the axolotl is particularly vulnerable to certain viral infections. Like other salamanders, the axolotl genome is one of the largest (32 Gb) and the impact of genome size on Ig loci architecture is unknown. To better understand the immune response in axolotl, we aimed to characterize the immunoglobulin loci of A. mexicanum and compare it with other model vertebrates. Methods: The most recently published genome sequence of A. mexicanum (V6) was used for alignment-based annotation and manual curation using previously described axolotl Ig sequences or reference sequences from other vertebrates. Gene models were further curated using A. mexicanum spleen RNA-seq data. Human, Xenopus tropicalis, Danio rerio (zebrafish), and eight tetrapod reference genomes were used for comparison. Results: Canonical A. mexicanum heavy chain (IGH), lambda (IGL), sigma (IGS), and the putative surrogate light chain (SLC) loci were identified. No kappa locus was found. More than half of the IGHV genes and the IGHF gene are pseudogenes and there is no clan I IGHV genes. Although the IGH locus size is proportional to genome size, we found local size restriction in the IGHM gene and the V gene intergenic distances. In addition, there were V genes with abnormally large V-intron sizes, which correlated with loss of gene functionality. Conclusion: The A. mexicanum immunoglobulin loci share the same general genome architecture as most studied tetrapods. Consistent with its large genome, Ig loci are larger; however, local size restrictions indicate evolutionary constraints likely to be imposed by high transcriptional demand of certain Ig genes, as well as the V(D)J recombination over very long genomic distance ranges. The A. mexicanum has undergone an extensive process of Ig gene loss which partially explains a reduced potential repertoire diversity that may contribute to its impaired antibody response.

Effect of Structural Ordering on the Charge Storage Mechanism of p-Type Organic Electrode Materials.

Understanding the properties that govern the kinetics of charge storage will enable informed design strategies and improve the rate performance of future battery materials. Herein, we study the effects of structural ordering in organic electrode materials on their charge storage mechanisms. A redox active unit, N,N'-diphenyl-phenazine, was incorporated into three materials which exhibited varying degrees of ordering. From cyclic voltammetry analysis, the crystalline small molecule exhibited diffusion-limited behavior, likely arising from structural rearrangements that occur during charge/discharge. Conversely, a branched polymer network displayed surface-controlled kinetics, attributed to the amorphous structure which enabled fast ionic transport throughout charge/discharge, unimpeded by sluggish structural rearrangements. These results suggest a method for designing new materials for battery electrodes with battery-like energy densities and pseudocapacitor-like rate capabilities.

Spatial heterogeneity of water quality in a highly degraded tropical freshwater ecosystem.

Awareness of environmental heterogeneity in ecosystems is critical for management and conservation. We used the Xochimilco freshwater system to describe the relationship between heterogeneity and human activities. This tropical aquatic ecosystem south of Mexico City is comprised of a network of interconnected canals and lakes that are influenced by agricultural and urban activities. Environmental heterogeneity was characterized by spatially extensive surveys within four regions of Xochimilco during rainy and dry seasons over 2 years. These surveys revealed a heterogeneous system that was shallow (1.1 m, SD=0.4 ), warm (17 degrees C, SD=2.9), well oxygenated (5.0 mg l(-1), SD=3), turbid (45.7 NTU SD = 26.96), and extremely nutrient-rich (NO(3)-N=15.9 mg l(-1), SD=13.7; NH(4)-N=2.88 mg l(-1), SD=4.24; and PO(4)-P=8.3 mg l(-1), SD=2.4). Most of the variables were not significantly different between years, but did differ between seasons, suggesting a dynamic system within a span of a year but with a high resilience over longer periods of time. Maps were produced using interpolations to describe distributions of all variables. There was no correlation between individual variables and land use. Consequently, we searched for relationships using all variables together by generating a combined water quality index. Significant differences in the index were apparent among the four regions. Index values also differed within individual region and individual water bodies (e.g., within canals), indicating that Xochimilco has high local heterogeneity. Using this index on a map helped to relate water quality to human activities and provides a simple and clear tool for managers and policymakers.

Influence of solid waste and topography on urban floods: The case of Mexico City.

Floods in cities are increasingly common as a consequence of multifactor watershed dynamics, including geomorphology, land-use changes and land subsidence. However, urban managers have focused on infrastructure to address floods by reducing blocked sewage infrastructure, without significant success. Using Mexico City as a case study, we generated a spatial flood risk model with geomorphology and anthropogenic variables. The results helped contrast the implications of different public policies in land use and waste disposal, and correlating them with flood hazards. Waste disposal was only related to small floods. 58% of the city has a high risk of experiencing small floods, and 24% of the city has a risk for large floods. Half of the population with the lowest income is located in the high-risk areas for large floods. These models are easy to build, generate fast results and are able to help to flood policies, by understanding flood interactions in urban areas within the watershed.

Trophic specialization and morphological divergence between two sympatric species in Lake Catemaco, Mexico.

The association of morphological divergence with ecological segregation among closely related species could be considered as a signal of divergent selection in ecological speciation processes. Environmental signals such as diet can trigger phenotypic evolution, making polymorphic species valuable systems for studying the evolution of trophic-related traits. The main goal of this study was to analyze the association between morphological differences in trophic-related traits and ecological divergence in two sympatric species, Astyanax aeneus and A. caballeroi, inhabiting Lake Catemaco, Mexico. The trophic differences of a total of 70 individuals (35 A. aeneus and 35 A. caballeroi) were examined using stable isotopes and gut content analysis; a subset of the sample was used to characterize six trophic and six ecomorphological variables. In our results, we recovered significant differences between both species in the values of stable isotopes, with higher values of δ15N for A. caballeroi than for A. aeneus. Gut content results were consistent with the stable isotope data, with a higher proportion of invertebrates in A. caballeroi (a consumption of invertebrates ten times higher than that of A. aeneus, which in turn consumed three times more vegetal material than A. caballeroi). Finally, we found significant relationship between ecomorphology and stable isotopes (r = .24, p < .01), hence, head length, preorbital length, eye diameter, and δ15N were all positively correlated; these characteristics correspond to A. caballeroi. While longer gut and gill rakers, deeper bodies, and vegetal material consumption were positively correlated and corresponded to A. aeneus. Our results are consistent with the hypothesis that morphological divergence in trophic-related traits could be associated with niche partitioning, allowing the coexistence of closely related species and reducing interspecific competition.

[Characteristics of Clostridium difficile infection in a high complexity hospital and report of the circulation of the NAP1/027 hypervirulent strain in Colombia].

INTRODUCTION: Clostridium difficile is the main pathogen related to healthcare-associated diarrhea and it is the cause of 20 to 30% of diarrhea cases caused by antibiotics. In Colombia and Latin America, the knowledge about the epidemiological behavior of this infection is limited. OBJECTIVE: To describe the characteristics of a series of patients with C. difficile infection. MATERIALS AND METHODS: We performed a descriptive case series study of patients with C. difficile infection hospitalized in the Fundación Clínica Shaio from January, 2012, to November, 2015. RESULTS: We analyzed 36 patients. The average age was 65 years. The risk factors associated with the infection were: previous use of antibiotics (94.4%), prior hospitalization in the last three months (66.7%) and use of proton pump inhibitors (50%). The most common comorbidities were chronic kidney disease (41.7%) and diabetes mellitus (30.6%). The most frequent symptoms were more than three loose stools per day (97.1%) and abdominal pain (42.9%). According to the severity of the disease, 44.4% of cases were classified as mild to moderate, 38.9% as severe, and 11.1% as complicated or severe. The detection of the toxin by PCR (GeneXpert) was the most common diagnostic procedure (63.8%). Global mortality during hospitalization was 8%. We identified four strains with serotype NAP1/027 and nine samples positive for binary toxin. CONCLUSION: Clostridium difficile infection should be suspected in patients with diarrhea and traditional risk factors associated with this disease. We report the circulation of the hypervirulent strain serotype NAP1/027 in Colombia, which should be countered with epidemiological surveillance and a prompt diagnosis.

From aquaculture goals to real social and ecological impacts: carp introduction in rural Central Mexico.

Aquaculture has been seen as a solution to food/protein availability in rural populations of poor countries. It is mainly based on exotic species, that produce changes in host system dynamics once introduced. Aquaculture not only changes the ecology of freshwater systems, but can also lead to modification of social relations. Until now, aquaculture programs have not been adequately analyzed no questioned enough. We evaluate both ecological effects and local social benefits of common carp aquaculture programs in shallow ponds of rural areas, using a municipality in Central Mexico as a case study. Using an "environmental entitlements" approach, our findings suggest that: i) carp aquaculture increases water turbidity and depletes native species reducing the poor people's access to them; ii) aquaculture mainly benefits pond owners rather than poor peasants. This mainly results from changes in fishing rights. We conclude that aquaculture policy goals and assumptions of benefits should be reviewed, if the negative ecological effects are to be decreased and conditions for people in rural areas are to be improved.

Quiste hidatídico pulmonar en paciente con diagnóstico de asma bronquial, a propósito de un caso / Hydatidpulmonary cyst in a patient with a diagnosis of bronchial asthma, on a case

La hidatidosis es una zoonosis distribuida mundialmente, causada por el Echinococcus granulosusen su fase larvaria. Prevalente en zonas agrícolas y ganaderas, su localización más habitual es hepática y pulmonar (>90 %), puede ser asintomática o manifestar síntomas de acuerdo con el órgano afecto o a la presencia de complicaciones. Es poco frecuente, siendo principalmente diagnosticada de manera incidental en estudios radiológicos de rutina. En Ecuador la incidencia de enfermedad hidatídica es baja a pesar de las condiciones epidemiológicas idóneas para el crecimiento del equinococo, en comparación con los países vecinos, donde la incidencia de esta enfermedad es superior, sin embargo, podrían faltar estudios que aporten datos estadísticos exactos que orienten hacia una realidad epidemiológica más clara de esta patología en el país.

Hydatidosis it's a worldwide distributed zoonosis, caused by the larval stage of Echinococcus granulosus. Prevalent in agricultural and livestock zones, the most common location is liver and lung (> 90 %), it can be asymptomatic or causing symptoms according with the injured organ or development of complications. Seems to be a rare condition, been in most cases incidentally diagnosed on a routine x-ray evaluation. Hydatid disease incidence in Ecuador is very low despite the epidemiological conditions suitable for the growth of Echinococcus, in comparison with neighboring countries where the incidence of this disease is higher. However, more studies could be needed to provide accurate statistics data than approach a clearer epidemiological reality of this disease in the country.

Reproduction and survival under different water temperatures of Gyrodactylus mexicanus (Platyhelminthes: Monogenea), a parasite of Girardinichthys multiradiatus in Central Mexico.

Gyrodactylid population growth may depend on abiotic variables such as temperature. We tested the survival and reproductive rate of Gyrodactylus mexicanus, a parasite infecting fins of Girardinichthys multiradiatus, at 3 different water temperatures, 10-13, 19-22, and 24 C. The temporal sequence of birth and age at death of each parasite isolated from the hosts was recorded through at least 8 generations. Our results showed that the average number of offspring per parasite was 2.0 when averaged across all temperatures. However, the generation time was negatively correlated with temperature. The innate capacity for increase (r(m)) was positively correlated with water temperature: from 0.29 parasite/day at 13 C to 0.48 parasite/day at 24 C. These data confirm that water temperature has a direct influence on parasite population dynamics. The current study represents the first contribution to understanding the population ecology of the monogenean G. mexicanus in central Mexico.

Características de la infección por Clostridium difficile en una institución de alta complejidad y reporte de la circulación en Colombia de la cepa hipervirulenta NAP1/027 / Characteristics of Clostridium difficile infection in a high complexity hospital and report of the circulation of the NAP1/027 hypervirulent strain in Colombia

Resumen Introducción. Clostridium difficile es el principal responsable de la diarrea asociada al uso de antibióticos. En Colombia y en Latinoamérica, el conocimiento sobre el comportamiento epidemiológico de la infección por C. difficile todavía es limitado. Objetivo. Describir las características de una serie de pacientes con infección por C.difficile . Materiales y métodos. Se hizo un estudio descriptivo de una serie de casos de pacientes con infección por C. difficile atendidos en la Fundación Clínica Shaio, entre enero de 2012 y noviembre de 2015. Resultados. Se estudiaron 36 pacientes con una edad promedio de 65 años. Se determinaron los siguientes factores relacionados con la infección por C. difficile: uso previo de antimicrobianos (94,4 %), hospitalización en los últimos tres meses (66,7 %) y uso de inhibidores de la bomba de protones (50 %). Las comorbilidades más comunes fueron la enfermedad renal crónica (41,7 %) y la diabetes mellitus (30,6 %). Los síntomas más frecuentes fueron más de tres deposiciones diarreicas (97,1 %) y dolor abdominal (42,9 %). En cuanto a la gravedad de los casos, 44,4 % se clasificó como leve a moderado, 38,9 % como grave, y 11,1 % como complicado o grave. El método de diagnóstico más utilizado (63,8% de los pacientes) fue la identificación de la toxina mediante reacción en cadena de la polimerasa (PCR). La mortalidad global durante la hospitalización fue de 8 %. Se identificaron cuatro cepas del serotipo NAP1/027 y nueve muestras fueron positivas para la toxina binaria. Conclusión. La infección por C. difficile debe sospecharse en pacientes con deposiciones diarreicas y factores asociados tradicionalmente a esta enfermedad. Se reportó la circulación de cepas hipervirulentas del serotipo NAP1/027 en Colombia, lo cual debe enfrentarse con la vigilancia epidemiológica y el diagnóstico temprano.

Abstract Introduction: Clostridium difficile is the main pathogen related to healthcare-associated diarrhea and it is the cause of 20 to 30% of diarrhea cases caused by antibiotics. In Colombia and Latin America, the knowledge about the epidemiological behavior of this infection is limited. Objective: To describe the characteristics of a series of patients with C. difficile infection. Materials and methods: We performed a descriptive case series study of patients with C. difficile infection hospitalized in the Fundación Clínica Shaio from January, 2012, to November, 2015. Results: We analyzed 36 patients. The average age was 65 years. The risk factors associated with the infection were: previous use of antibiotics (94.4%), prior hospitalization in the last three months (66.7%) and use of proton pump inhibitors (50%). The most common comorbidities were chronic kidney disease (41.7%) and diabetes mellitus (30.6%). The most frequent symptoms were more than three loose stools per day (97.1%) and abdominal pain (42.9%). According to the severity of the disease, 44.4% of cases were classified as mild to moderate, 38.9% as severe, and 11.1% as complicated or severe. The detection of the toxin by PCR (GeneXpert) was the most common diagnostic procedure (63.8%). Global mortality during hospitalization was 8%. We identified four strains with serotype NAP1/027 and nine samples positive for binary toxin. Conclusion: Clostridium difficile infection should be suspected in patients with diarrhea and traditional risk factors associated with this disease. We report the circulation of the hypervirulent strain serotype NAP1/027 in Colombia, which should be countered with epidemiological surveillance and a prompt diagnosis.

Fish functional groups in a tropical wetland of the Yucatan Peninsula, Mexico

La caracterización de los rasgos funcionales de las especies es un paso importante en la comprensión y descripción de las comunidades en hábitats naturales. La clasificación de especies en grupos funcionales es una herramienta útil para identificar la redundancia y la especialización. Se estudió la comunidad de peces de un humedal prístino de agua dulce en la Reserva de la Biosfera de Sian Ka'an, analizando dos funciones multidimensionales: adquisición de alimento y la locomoción. Analizamos los cambios en la estructura de los grupos funcional entre hábitats (permanentes y temporales) y temporadas (lluvias y secas). Seis grupos funcionales con características ecológicas distintas fueron detectados, dos de los cuales presentaron una alta redundancia funcional y tres de ellos están representados únicamente por una especie con una función ecológica particular. En las pozas permanentes durante la temporada de secas, la riqueza y diversidad de grupos funcionales fueron menores; mientras que la equitatividad de grupos funcionales fue mayor. Durante la temporada de lluvias se detectaron todos los grupos funcionales y la estructura de los grupos fue similar entre los hábitat. Estos resultados sugieren que los filtros ambientales tienen un efecto durante la temporada de secas y la complementariedad de nicho durante la temporada de lluvias.

The characterization of species' functional traits is a major step in the understanding and description of communities in natural habitats. The classification of species into functional groups is a useful tool to identify redundancy and uniqueness. We studied the fish community of a pristine freshwater wetland in the Sian Ka'an Biosphere Reserve by analysing two multidimensional functions: food acquisition and locomotion. We investigated changes in the functional group structure between habitats (permanent and temporary pools) and seasons (dry and wet). Six functional groups with different ecological characteristics were detected, two of which had high functional redundancy and three of them were represented by single species with unique ecological functions. In permanent pools during the dry season, functional group richness and diversity were lower, while evenness was higher. During the wet season, all functional groups were detected and similar functional group structure was found between habitats. These results suggest an effect of environmental filtering during the dry season and niche complementarity during the wet season.

Fish diet composition in permanent and semi-permanent pools in tropical wetlands of the Yucatan Peninsula

We compared fish diet composition between permanent (P) and semi-permanent (SP) pools in Petenes Biosphere Reserve (PBR), Campeche. A total of 445 gut contents were examined to determine stomach relative fullness (RF), fish diet as index of niche breadth (INB) and diet overlap. In SP pools, species showed a RF of 1.66 (57.20 % empty stomachs) whereas in P pools, the RF was 2.91 (31.16%). We classified fish diet into six trophic groups: detritivorous, herbivorous-detritivorous, insectivorous, piscivorous, omnivorous and malacophagous. Species in P pools were found to be specialist. Conversely, species present in both habitats shifted to generalist patterns. There was a 54.0% dissimilarity in fish diet composition between pools. From all items identified, detritus (21.33% of the total dissimilarity), aquatic and terrestrial invertebrates (12.31%), fish remains (10.29%), plant remains (7.37%), and crustaceans (2.74%) distinguished diets between pools. Significant diet overlaps (>0.6) and low INB values (<0.3) were observed in P pools, whereas in SP pools, intermediate-low diet overlaps (<0.4) and higher INB values (>0.5) were observed. In SP pools seasonality had a strong effect on fish diet, increasing the frequency of food items such as terrestrial insects, amphipods and arachnids, during the rainy season while P pools showed lower variation. Thus, fish trophic habits appear to be regulated by pools hydrology.

Se analizaron y compararon los contenidos estomacales de la ictiofauna en cuerpos de agua permanentes (P) y semi-permanente (SP) de la reserva de la Biosfera Los Petenes, Campeche. Se analizaron un total de 445 estómagos en los cuales se determino la diversidad de dieta (como Índice de amplitud de nicho = INB), plenitud relativa de estómagos (PRE) y traslape de dietas. En las pozas SP 57.20 % de los estómagos se encontraron vacíos y los estómagos con alimento presentaron un PRE de 1.66. En las pozas P solo el 31.16 % de los estómagos se encontraron vacíos y un PRE de 2.91. Los peces se clasificaron en seis grupos tróficos: detritívoros, herbívoros-detritívoros, insectívoros, piscívoros, omnívoros y malacófagos. Los individuos en la pozas P tendieron a presentar dietas especializadas mientras que en las pozas SP patrones generalistas. Se observo una disimilitud de dietas entre pozas del 54.0 % asociada a los items: detritus (21.33%), invertebrados acuáticos y terrestres (12.31%), fragmentos de peces (10.29%), fragmentos de vegetación (7.37%) y crustáceos (2.74%). Los mayores traslapes de dietas (> 0.6) y menores INB (< 0.3) se observaron en especies presentes en las pozas P mientras que en las pozas SP se observaron valores de traslape intermedios-bajos (<0.4) e INB mayores (> 0.5) en especies que utilizaron mayores fuentes de alimento. En las pozas SP la estacionalidad tuvo una marcada influencia en la proporción de los ítems: insectos acuáticos, anfípodos y arácnidos, los cuales presentaron mayores frecuencias, sobre todo en la época de lluvias, mientras que las pozas P no presentaron cambios significativos. Los resultados sugieren que los peces en pozas de la RBP modifican su dieta en función de la hidrología de los cuerpos de agua, con un patrón trófico particular a escala regional comparado con otros cuerpos de agua estacionales en Centro y América del Sur.

Chytridiomycosis survey in wild and captive mexican amphibians.

Mexico, a rich country in terms of amphibian diversity, hosts about 375 described species. Population declines have been documented for several species where it is evident that their habitat is being destroyed or modified. However, other species which inhabit pristine areas are declining as well. It has been suggested that the chytrid fungus Batrachochytrium dendrobatidis (B.d.) may be one of the causes of the enigmatic declines in Mexico. We surveyed a total of 45 localities, in 12 states across Mexico, examining a total of 360 specimens representing 14 genera and 30 species. We also examined 91 specimens of Ambystoma mexicanum from a captive population in Mexico City as well as one Pachymedusa dacnicolor obtained in a pet shop. We used a two-tiered technique to detect the pathogen. For wild-caught specimens, we utilized light microscopy to identify presence of B.d. sporangia in amphibian skin. Then, to verify the infection, we used a quantitative real-time PCR assay on collected skin sections which is specific for B.d. For captive animals, we used a nonlethal version of the real-time PCR technique. We found evidence of B.d. infection in 111 animals comprising 14 species in 13 localities. A large percentage (84%) of Ambystoma mexicanum from the colony were infected with B.d. The two most highly infected individuals were the endangered Ambystoma mexicanum, from a captive colony, and Pachymedusa dacnicolor, purchased at a pet shop.