Browsing by Autor "Ximena Aguilera"

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Asexuality and polyploidy in Daphnia from the tropical Andes
(Wiley, 2007) Ximena Aguilera; Joachim Mergeay; An Wollebrants; Steven Declerck; Luc De Meester
We assessed genetic variation at microsatellite loci within and among populations of the planktonic crustacean Daphnia pulex in 12 Bolivian Andean lakes, located above 4,000 m above sea level. Genetic analyses show that all populations consisted of obligately asexual lineages, a fact that was confirmed by observations from laboratory cultures. Moreover, microsatellite phenotypes indicate that these tropical lineages are polyploid. Levels of genetic diversity were comparable to those found in polyploid Daphnia from arctic regions, indicating a local origin rather than an accidental colonization from arctic regions. This is the first record of polyploid cladocerans in a tropical region. We suggest that their origination and abundance have probably been facilitated by the extreme environmental conditions in Andean lakes. Our analysis of multilocus genotype frequencies in relation to variation in environmental conditions indicates lineage sorting along a food availability and fish predation gradient.
Distribution patterns, population status and conservation of Melanosuchus niger and Caiman yacare (Crocodylia, Alligatoridae) in oxbow lakes of the Ichilo river floodplain, Bolivia
(Vicerractoría Investigación, 2007) Ximena Aguilera; Jorge S. Coronel; Thierry Oberdorff; Paul A. Van Damme
Caiman yacare (lagarto) and Melanosuchus niger (black caiman), sympatric species in the Bolivian Amazon basin, have been severely overexploited in the past. We present the results of a standardized survey of C. yacare and M. niger populations in order to evaluate their actual population status in twelve oxbow lakes of the Ichilo River floodplain. Additionally we explored the effect of environmental and anthropogenic variables on caiman distribution patterns. The average density of C yacare and M niger in the shoreline of floodplain lakes was of 6 and 1 ind/km, respectively. For both species, the population was composed mainly of juvenile individuals. We used regression tree analysis (RTA) to assess patterns of M. niger and C. yacare densities with eight environmental and two anthropogenic variables. The RTA analysis showed that the variation in the densities of both C. yacare (52.4%) and M. niger (36.8 %) was related to water conductivity. For C yacare, higher densities occurred at higher values of water conductivity, while M. niger densities followed an opposite trend, resulting in relatively well spatially segregated populations of the two species. After excluding conductivity, Lake-River Distance (LRD) was shown to be the main splitting variable in the RTA analysis. The observed distribution patterns may be the result of the historical post-hunting situation, in combination with differences in habitat selection by the two species, and competitive exclusion processes between the two species. M. niger, a species reported to be recovering slowly from previous low population levels, appears relatively well protected in the Ichilo river floodplain.
Estructura de la comunidad zoobentónica de la laguna Bufeos (Cochabamba, Bolivia)
(1999) Ximena Aguilera; Edgar Goïtia
STRUCTURE OF THE ZOOBENTHIC COMMUNITY OF THE LAGUNA BUFEOS (COCHABAMBA, BOLIVIA) Las lagunas de la varzea del rio Ichilo sufren fluctuaciones hidrologicas estacionales producto de la inundacion, que determina dos epocas: aguas bajas yaguas altas. Este estudio describe la estructura de la comunidad zoobentonica de la laguna Bufeos, en estas dos epocas hidrologicas, estableciendo su relacion con los factores ambientales. Se encontraron 31 especies de macroinvertebrados, de las cuales se presentan 28 en aguas bajas (1877 org/m2) y 25 en aguas altas (1969 org/m2). Se determino que no existen diferencias significativas de composicion y abundancia zoobentonica, ni espacial ni temporalmente. Tanto en epoca de aguas bajas como altas, fue Chaoborus sp. (Diptera) la especie de mayor abundancia, seguida en orden de importancia por Procladius sp. (Diptera) y Oligochaeta, otras especies importantes numericamente fueron Pisidium sterkianum y Campsurus sp. Desde un punto de vista funcional, la composicion y abundancia muestran que los organismos zoobentonicos son depredadores en su mayor parte. La abundancia de los organismos se correlaciona con la profundidad, temperatura y oxigeno disuelto. Se concluye que la comunidad zoobentonica de la laguna Bufeos, es estable espacial y temporalmente, condicionada por los cortos periodos de inundacion. Palabras clave: Zoobentos, varzea, Laguna Bufeos, Bolivia. ABSTRACT The lakes on the ffood plain of the Ichilo river suffer seasonal hidrological ffuctuations caused by the ffood. It determine two periods in the place: wet season and dry season. This study describes the structure of the zoobenthic community of one of this lakes (Laguna Bufeos) in these two hidrological periods and at the same time the relationships between zoobenthic structure and environmental factors are try to established. 31 species were found, only 28 of this in dry season (1877 org./m2) and 25 in wet season (1969 org./m2). The Stadistic analysis dind't find significative differences on benthic community between dry season and wet season. In both seasons Chaoborus sp. had the majar abundance followed by Procladius sp. (Diptera) and Oligochaeta. Other important species were Pisidium sterkianum and Campsurus sp.. The functional composition of the benthic community and its relative abundance shows that the predators are the most abundant. The relationship between the environmental factors and the structure of zoobentic community show be important with deep, temperature and dissolved oxigen in both seasons. The zoobenthic community of the Laguna Bufeos is stable in time and space, the small periods of ffood determine a relatively stable environment for this zoobenthic organismo Key words: Zoobentos, varzea, Laguna Bufeos, Bolivia.
Resúmenes de la Primera Jornada del Grupo de Catálisis de la Universidad Pedagógica y Tecnológica de Colombia (GC-UPTC)
(Pedagogical and Technological University of Colombia, 2022) Carlos Cifuentes-Espitia; Jaime Portilla; Ximena Aguilera; Laura Barbelli; D. Lick; M. Casella; L. Pizzio; Manuel Gregorio Loza-Murguia; Eliana Nope; Ángel G. Sathicq
Se presentan los resúmenes de la primera Jornada de Catálisis de la Universidad Pedagógica y Tecnológica de Colombia. Esta conferencia permitirá en poco tiempo potencializar la apropiación social del conocimiento en esta área de la ciencia a nivel regional, brindando oportunidades para que los participantes expongan sus trabajos, y facilitando la difusión del conocimiento científico en esta área.
The genetic legacy of polyploid Bolivian Daphnia: the tropical Andes as a source for the North and South American D. pulicaria complex
(Wiley, 2008) Joachim Mergeay; Ximena Aguilera; Steven Declerck; Adam Petrusek; Tine Huyse; Luc De Meester
We investigated genetic variation in asexual polyploid members of the water flea Daphnia pulex complex from a set of 12 Bolivian high-altitude lakes. We used nuclear microsatellite markers to study genetic relationships among all encountered multilocus genotypes, and combined this with a phylogenetic approach using DNA sequence data of three mitochondrial genes. Analyses of mitochondrial gene sequence divergence showed the presence of three very distinct clades that likely represent cryptic undescribed species. Our phylogenetic results suggest that the Daphnia pulicaria group, a complex of predominantly North American species that has diversified rapidly since the Pleistocene, has its origin in South America, as specific tests of topology indicated that all three South American lineages are ancestral to the North American members of this species group. A comparison between variation of nuclear and mitochondrial markers revealed that closely related polyploid nuclear genotypes sometimes belonged to very divergent mitochondrial lineages, while distantly related nuclear genotypes often belonged to the same mitochondrial lineage. This discrepancy suggests that these South American water fleas originated through reciprocal hybridization between different endemic, sexually reproducing parental lineages. It is also likely that polyploidy of the investigated lineages resulted from this hybridization. Nevertheless, no putative diploid parental lineages were found in the studied region.