La biodiversidad y evolución en ambientes acuáticos analizadas con herramientas moleculares

Molecular tools constitute an universal, unprecedented instrument to study the origin and evolution of biological diversity of complex aquatic systems. These tools, including molecular markers and new theoretical and statistical models to analyze them, have helped to reveal patterns and processes about biodiversity, population genetics, phylogeography and evolution of organisms that inhabit these systems, which previously was not possible with conventional tools. Advances included: 1) the discovery of a large number of species, particularly microorganism, and the knowledge of the complexity and functionality of aquatic microbial communities, 2) the unveiling of the genetic structure to finescale, 3) the extension of the knowledge about the phylopatry behavior, the connection between populations and the evolutionary history of gene lineages and 4) the description of the origin, radiation patterns, adaptation and coevolution at macroevolutive scale from different taxa. The continuous improvement of these tools and the integration of other disciplines help to have a more complete vision on biodiversity, ecology and evolution in these systems.Las herramientas moleculares constituyen un instrumento universal, sin precedentes, que ha revitalizado el estudio del origen y la evolución de la diversidad biológica de los complejos sistemas acuáticos. Estas herramientas, que incluyen marcadores moleculares y nuevos modelos teóricos y estadísticos para analizarlos, han ayudado a revelar patrones y procesos sobre biodiversidad, genética de poblaciones, filogeografía y evolución de los organismos que habitan estos sistemas, lo cual anteriormente no era posible hacer con las herramientas clásicas. Entre los avances obtenidos destacan: 1) el descubrimiento de una gran cantidad de especies, particularmente de microorganismos, y con ello el conocimiento de la complejidad y funcionalidad de las comunidades microbianas acuáticas, 2) la revelación de la estructura genética a escala fina, 3) la ampliación del conocimiento de las conductas filopátridas, la conexión entre poblaciones y la historia evolutiva de los linajes y 4) la descripción del origen, patrones de radiación, adaptación y coevolución a nivel macroevolutivo de diferentes taxones. El continuo mejoramiento de estas herramientas y la integración de otras disciplinas, ayudarán a tener una visión más completa sobre la biodiversidad, ecología y evolución en estos sistemas

Alternative glacial-interglacial refugia demographic hypotheses tested on Cephalocereus columna-trajani (Cactaceae) in the intertropical Mexican drylands

Historic demography changes of plant species adapted to New World arid environments could be consistent with either the Glacial Refugium Hypothesis (GRH), which posits that populations contracted to refuges during the cold-dry glacial and expanded in warm-humid interglacial periods, or with the Interglacial Refugium Hypothesis (IRH), which suggests that populations contracted during interglacials and expanded in glacial times. These contrasting hypotheses are developed in the present study for the giant columnar cactus Cephalocereus columna-trajani in the intertropical Mexican drylands where the effects of Late Quaternary climatic changes on phylogeography of cacti remain largely unknown. In order to determine if the historic demography and phylogeographic structure of the species are consistent with either hypothesis, sequences of the chloroplast regions psbA-trnH and trnT-trnL from 110 individuals from 10 populations comprising the full distribution range of this species were analysed. Standard estimators of genetic diversity and structure were calculated. The historic demography was analysed using a Bayesian approach and the palaeodistribution was derived from ecological niche modelling to determine if, in the arid environments of south-central Mexico, glacial-interglacial cycles drove the genetic divergence and diversification of this species. Results reveal low but statistically significant population differentiation (FST = 0.124, P < 0.001), although very clear geographic clusters are not formed. Genetic diversity, haplotype network and Approximate Bayesian Computation (ABC) demographic analyses suggest a population expansion estimated to have taken place in the Last Interglacial (123.04 kya, 95% CI 115.3–130.03). The species palaeodistribution is consistent with the ABC analyses and indicates that the potential area of palaedistribution and climatic suitability were larger during the Last Interglacial and Holocene than in the Last Glacial Maximum. Overall, these results suggest that C. columna-trajani experienced an expansion following the warm conditions of interglacials, in accordance with the GRH

Quaternary origin and genetic divergence of the endemic cactus Mammillaria pectinifera in a changing landscape in the Tehuacán Valley, Mexico

The endemic Mexican cactus, Mammillaria pectinifera, shows low dispersal capabilities and isolated populations within the highly dissected landscape of Tehuacan Valley. These characteristics can restrict gene flow and act upon the genetic divergence and speciation in arid plants. We conducted a phylogeographic study to determine if the origin, current distribution, and genetic structure of M. pectinifera were driven by Quaternary geomorphic processes. Sequences of the plastids psbA-trnH and trnT-trnL obtained from 66 individuals from seven populations were used to estimate genetic diversity. Population differentiation was assessed by an analysis of molecular variance. We applied a stepwise phylogenetic calibration test to determine whether species origin and genetic divergence among haplotypes were temporally concordant with recognizable episodes of geomorphic evolution. The combination of plastid markers yielded six haplotypes, with high levels of haplotype diversity (h = 0.622) and low nucleotide diversity (p = 0.00085). The populations were found to be genetically structured (F-ST = 0.682; P < 0.00001), indicating that geographic isolation and limited dispersal were the primary causes of genetic population differentiation. The estimated origin and divergence time among haplotypes were 0.017-2.39 and 0.019-1.237 mya, respectively, which correlates with Pleistocene tectonics and erosion events, supporting a hypothesis of geomorphically-driven geographical isolation. Based on a Bayesian skyline plot, these populations showed long term demographic stability, indicating that persistence in confined habitats has been the main response of this species to landscape changes. We conclude that the origin and haplotype divergence of M. pectinifera were a response to local Quaternary geomorphic evolution

Diversidad de maiz en la sierra sur de Oaxaca, México: conocimiento y manejo tradicional.

El estado de Oaxaca representa un importante acervo de maíz en México. Estudios previos han indicado la presencia de muchas variedades locales y razas agronómicas en la Sierra Norte y Valles Centrales. La Sierra Sur ha sido poco estudiada a pesar de la presencia de comunidades indígenas zapotecas, las cuales cultivan maíz, entre otras especies, y han preservado las variedades locales. El presente estudio responde a las siguientes preguntas: ¿cuál es la diversidad de maíz en términos de variedades tradicionales y razas agronómicas en la región zapoteca de Los Loxicha?, ¿la diversidad de maíz sigue un patrón de distribución a lo largo de un gradiente altitudinal?, ¿cuáles prácticas promueven y mantienen esta diversidad? Para contestar estas preguntas se realizó un estudio en cinco municipios de la Sierra Sur de Oaxaca. Durante 2007 se aplicaron entrevistas estructuradas a 930 agricultores para describir el proceso de manejo de semilla. La caracterización morfológica de las razas agronómicas se basó en muestras de mazorcas obtenidas en 375 milpas, con 20 plantas por milpa. Se encontraron altos niveles de diversidad local de maíz, con 36 variedades tradicionales correspondientes a 10 razas agronómicas. Las razas exhibieron diferencias en términos de variación fenotípica, distribución altitudinal y algunas muestran adaptación local. Los agricultores practican algunas formas de manejo ancestral para la selección de mazorcas y semillas, manteniendo, así, ciertos niveles de diferenciación entre las variedades y las razas agronómicas. Sin embargo, al sembrar diferentes variedades dentro de la misma parcela, se promueve el flujo génico y la introgresión entre ellas, manteniendo y promoviendo la diversidad fenotípica y genética

Educación cooperativa : experiencias escolares significativas

Fil: Ferreyra, Horacio Ademar. Universidad Católica de Córdoba. Facultad de Educación; Argentin

Educación cooperativa: experiencias escolares significativas

Fil: Ferreyra, Horacio Ademar. Universidad Católica de Córdoba. Facultad de Educación; Argentin

Population expansion and genetic structure in Cephalocereus nizandensis (Cactaceae), a microendemic cactus of rocky outcrops of the Tehuantepec basin, Mexico

Background and aims – Cephalocereus nizandensis is a microendemic columnar cactus that grows isolated in xerophytic enclaves associated with rocky outcrops in the Isthmus of Tehuantepec, in the south of Mexico. Its demographic history and genetic structure were assessed to determine the main events that shaped its current restricted distribution.Material and methods – Chloroplast intergenic sequences of 40 individuals and inter simple sequence repeats (ISSRs) of 45 individuals from four isolated populations were used to estimate haplotypic and nucleotide diversity, using expected heterozygosity and the Shannon index. AMOVA, population pair-wise FST, and Bayesian clustering analyses were performed to explore the genetic structure. Demographic history was estimated with neutrality tests, mismatch distribution analysis, and Bayesian skyline plots. Phylogenetic relationships and divergence times were determined using a median joining network and a Bayesian molecular clock.Key results – C. nizandensis has a high diversity and moderate genetic differentiation. The lowest elevation locality was found to be the most genetically distinct. The species has undergone a process of population expansion that began 150,000 years ago and has remained without evidence of a population contraction in the transition from the Pleistocene to the Holocene (11,700 years ago).Conclusions – C. nizandensis presents moderate but significant genetic differentiation, which may be due to an early divergence of its populations. Currently observed levels of genetic diversity are the result of historical maintenance of high population sizes and a population expansion approximately in the last 150,000 years, which was sustained independently of the climatic fluctuations of the Early Quaternary, due in part to the stability of the rocky habitat