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6082 results, page 1 of 10

Phylogeography and conservation genetics of a distinct lineage of sunfish in the Cuatro Ciénegas Valley of Mexico


"The valley of Cuatro Ciénegas, an aquatic oasis located in the Mexican Chihuahuan Desert, exhibits the highest level of endemism in North America and is a Mexican National Protected Area. However, little is known about the evolutionary distinctiveness of several vertebrate species present in the Cuatro Ciénegas valley. We conducted a phylogeographic study using mitochondrial haplotypes from the centrarchid fish Lepomis megalotis to determine if the populations found within the valley were evolutionarily distinct from populations outside the valley. We also examined if there was evidence of unique haplotypes of this sunfish within the valley. Genetic divergence of L. megalotis suggests populations within the valley are evolutionarily unique when compared to L. megalotis outside the valley. Significant mitochondrial sequence divergence was also discovered between L. megalotis populations on either side of the Sierra de San Marcos that bisects the valley. Our results reinforce previous studies that suggest the organisms occupying aquatic habitats not only within Cuatro Ciénegas but also in each of the two lobes of the valley generally deserve independent consideration during management decisions."


Sunfish, phylogeography, conservation genetics, Cuatro Ciénegas, Mexico BIOLOGÍA Y QUÍMICA CIENCIAS DE LA VIDA GENÉTICA GENÉTICA DE POBLACIONES

Modelo econométrico de la demanda del agua de los acuíferos Valle de Cuatro Ciénegas y Valle El Hundido.


Tesis (Maestría en Ciencias, especialista en Economía).- Colegio de Postgraduados, 2015.

La expansión agrícola y pecuaria ha originado un incremento en la demanda de agua en Cuatro Ciénegas, Coahuila. La presión por el uso del agua pone en peligro de destrucción los cauces y pozas naturales, así como las diferentes especies endémicas presentes en la región. Para determinar la relación, de la demanda de agua y su precio se estimó un modelo de ecuaciones simultáneas compuesto de tres funciones de demanda (pecuario, agrícola y doméstico) y cuatro identidades. Se utilizaron datos anuales con series históricas de 1993-2013. Los resultados muestran que la demanda precio del agua es inelástica en los tres sectores, con elasticidades de -0.045 para el sector agrícola de riego, -0.160 para el sector pecuario y -0.034 para el doméstico. Los resultados indican que el consumo del agua en el doméstico es insensible a cambio en el precio, los interesados sobre el uso y consumo del agua y las políticas que tratan de diseñar e implementar que deben considerar el aumento de los precios en los sectores. Una disminución de 1% sobre el consumo de agua en los tres sectores agrícola, pecuario y residencial podría lograrse mediante un aumento en el precio del agua en 22.2, 6.3 y 29.4%, respectivamente. Debido a la importancia de Cuatro Ciénegas en la preservación de pozas y especies, que convierten al valle un laboratorio natural, se recomienda disminuir el consumo de agua en aquel sector con un menor valor de uso como es el sector agrícola. _______________ ECONOMETRIC MODEL OF THE WATER DEMAND FROM AQUIFERS FROM “CUATRO CIENEGAS” AND “HUNDIDO” VALLEYS. ABSTRACT: The agricultural and livestock expansion has caused an increase in the water demand in Cuatro Ciénegas, Coahuila. The pressure due to the use of water puts riverbeds and natural pools at risk, as well as the different endemic species in the region. To determine the ratio of water demand and its price a model of simultaneous equations composed of three demand functions (livestock, agricultural and domestic) and four identities are estimated. Annual data with historical series from 1993 to 2013 was used in order to calculate elasticities. The results of the equation show that the demand of water regarding the change in prices is inelastic, showing elasticities of -0.045 for the irrigation agricultural sector, -0.160 for the livestock sector, and -0.034 for the domestic sector. The results indicate that water consumption in the agricultural and domestic sectors is imperceptible towards changes in prices. People interested in the use and consumption, and in the policies intended to be designed and implemented, should consider the increase in prices sectors. A decrease of 1% on water consumption in the three agricultural, livestock and residential sectors could be achieved by increasing the price of water to 22.22, 6.25, and 29.41%, respectively. Due to the importance of Cuatro Ciénegas regarding the natural pools and species conservation, which turns the valley into a natural laboratory, it is recommended to reduce water consumption in that sector, which owns a less-value use just like the agricultural sector.

Master thesis

Cuatro Ciénegas Demanda de agua Elasticidades Sector agrícola, pecuario y doméstico Modelo ecuaciones simultáneas Water demand Elasticities Agricultural, livestock, and domestic sectors Simultaneous equations models Economía Maestría CIENCIAS SOCIALES CIENCIAS ECONÓMICAS ECONOMETRÍA MODELOS ECONOMÉTRICOS

The effect of aquatic plant abundance on shell crushing resistance in a freshwater snail


"Most of the shell material in snails is composed of calcium carbonate but the organic shell matrix determines the properties of calcium carbonate crystals. It has been shown that the deposition of calcium carbonate is affected by the ingestion of organic compounds. We hypothesize that organic compounds not synthesized by the snails are important for shell strength and must be obtained from the diet. We tested this idea indirectly by evaluating whether the abundance of the organic matter that snails eat is related to the strength of their shells. We measured shell crushing resistance in the snail Mexipyrgus churinceanus and the abundance of the most common aquatic macrophyte, the water lily Nymphaea ampla, in ten bodies of water in the valley of Cuatro Cienegas, Mexico. We used stable isotopes to test the assumption that these snails feed on water lily organic matter. We also measured other factors that can affect crushing resistance, such as the density of crushing predators, snail density, water pH, and the concentration of calcium and phosphorus in the water. The isotope analysis suggested that snails assimilate water lily organic matter that is metabolized by sediment bacteria. The variable that best explained the variation in crushing resistance found among sites was the local abundance of water lilies. We propose that the local amount of water lily organic matter provides organic compounds important in shell biomineralization, thus determining crushing resistance. Hence, we propose that a third trophic level could be important in the coevolution of snail defensive traits and predatory structures."


Mexipyrgus churinceanus, Nymphaea ampla, freshwater snail, Cuatro Ciénegas, Mexico BIOLOGÍA Y QUÍMICA CIENCIAS DE LA VIDA BIOLOGÍA ANIMAL (ZOOLOGÍA) DESARROLLO ANIMAL

Genetic structure and diversity in an isolated population of an endemic mole salamander (Ambystoma rivulare Taylor, 1940) of central Mexico


Human activities are affecting the distribution of species worldwide by causing fragmentation and isolation of populations. Isolation and fragmentation lead to populations with lower genetic variability and an increased chance of inbreeding and genetic drift, which results in a loss of biological fitness over time. Studies of the genetic structure of small and isolated populations are critically important for management and conservation decisions. Ambystoma rivulare is a micro-endemic Mexican mole salamander from central Mexico. It is found in the most ecologically disturbed region in Mexico, the Trans-Mexican Volcanic Belt. The goal of this study of the population genetics of the micro-endemic mole salamander was to provide information to be used as a basis for future research and conservation planning of this species and other species of the Ambystoma genus in Mexico. The structural analysis found two subpopulations, one for each river sampled, with no signs of admixture and very high levels of genetic differentiation. Medium to high levels of heterozygosity and few alleles and genotypes were observed. Evidence of an ancestral genetic bottleneck, low values of effective population size, small inbreeding coefficients, and low gene flow were also found.

The Universidad Autónoma del Estado de México funded the study (3047-2011E). R.L.H-B is grateful to CONACYT and COMECYT (359990 and 16BTID0028) for scholarships.


Mole salamander Conservation genetics Micro-endemic species M Microsatellites Co Conservation Int MEDICINA Y CIENCIAS DE LA SALUD

Algoritmo genético multi-objetivo para el descubrimiento de secuencias reguladoras


In some areas such as biology and medicine, it is important to understand de

behavior and functionality of living organism in a genetic level. The main reason is that

every organism is controlled by short strings of genetic code called genes. To active

gen it must receive a directive of the DNA and RNA segments known as regulatory

sequence. To find a regulatory sequence is fundamental to search motives inside of

the genetic code. A motive is a short sequence made of nucleotides that repeat in

certain region of the DNA, commonly near a gen. One technique that has been used to

search regulatory sequence is Genetic Algorithm. These stochastic searches, based on

evolution of the species, are based on the improvement of individual characteristic

through breeding of itself. Since the motive and different characteristic complexity an

approach of a mono-objective is not enough since motives have many qualities and

not every quality is in all motives. Because of this, the use of a multi-objective

algorithm is proposed. This is in order to find most of the motives and, in this way, be

able regulatory sequences. The obtained results show that this method is well suited

to do the task. This is because it found high conserved regions and, also, there are

sequences inside those founded by other methods. Another advantage is that our

algorithm was capable on finding big sequence with a length of 18bp (base pair). This is

important because is less probable to find a random patron without biological meaning

with big sequences.

En algunas áreas como la biología y la medicina, es de suma importancia

entender el comportamiento y funcionamiento de los seres vivos a un nivel genético.

Esto se debe, principalmente, a que los seres vivos son regulados por segmentos de

código llamados genes. Para que un gen se active debe recibir una directriz de

segmentos del ADN y ARN conocidos como secuencias reguladoras. Para encontrar una

secuencia reguladora es fundamental buscar motivos dentro del código genético. Un

motivo es una secuencia de nucleótidos que se repite en determinadas regiones del

ADN, comúnmente cerca de los genes. Una de las técnicas que se han utilizado para

realizar la búsqueda de secuencias reguladoras son los Algoritmos Genéticos. Estas

búsquedas estocásticas, basadas en la evolución de las especies, se basan en el

perfeccionamiento de las características de los individuos mediante el

entrecruzamiento (reproducción) de los mismos, con una continua evaluación. Dada la

complejidad de los motivos y las diferentes características que tienen, un

acercamiento con un solo objetivo es insuficiente dado que cada motivo puede tener

diferentes cualidades y no todas las cualidades se repiten en todos los motivos. Debido

a esto, se plantea el uso de varios objetivos (optimización multi-objetivo). Esto se hace

para encontrar la mayor cantidad de motivos y de esta forma obtener las secuencias

reguladoras. Los resultados obtenidos muestran que el método es competente para la

tarea, ya que ha encontrado regiones altamente conservadas y, también, se han

encontrado secuencias dentro de las cuales se han observado subsecuencias

obtenidas por otros métodos. Otra ventaja del método propuesto es que fue capaz de

encontrar secuencias de gran tamaño con una longitud de hasta 18bp (“base pair” o

pares de bases). Esto es importante debido que, entre más larga es la cadena, menos

probable es que sea un patrón aleatorio sin significado biológico.

Master thesis