ABSTRACT
Studies of genetic differentiation in fragmented environments help us to identify those landscape features that most affect gene flow and dispersal patterns. Particularly, the assessment of the relative significance of intrinsic biological and environmental factors affecting the genetic structure of populations becomes crucial. In this work, we assess the current dispersal patterns and population structure of Ctenomys "chasiquensis", a vulnerable and endemic subterranean rodent distributed on a small area in Central Argentina, using 9 polymorphic microsatellite loci. We use landscape genetics approaches to assess the relationship between genetic connectivity among populations and environmental attributes. Our analyses show that populations of C. "chasiquensis" are moderately to highly structured at a regional level. This pattern is most likely the outcome of substantial gene flow on the more homogeneous sand dune habitat of the Northwest of its distributional range, in conjunction with an important degree of isolation of eastern and southwestern populations, where the optimal habitat is surrounded by a highly fragmented landscape. Landscape genetics analysis suggests that habitat quality and longitude were the environmental factors most strongly associated with genetic differentiation/uniqueness of populations. In conclusion, our results indicate an important genetic structure in this species, even at a small spatial scale, suggesting that contemporary habitat fragmentation increases population differentiation.
Subject(s)
Rodentia/genetics , Animals , Argentina , Ecosystem , Gene Flow , Genetic Variation , Genotyping Techniques , Linkage Disequilibrium , Microsatellite Repeats , PhylogeographyABSTRACT
In this study we combine information from landscape characteristics, demographic inference and species distribution modelling to identify environmental factors that shape the genetic distribution of the fossorial rodent Ctenomys. We sequenced the mtDNA control region and amplified 12 microsatellites from 27 populations distributed across the Iberá wetland ecosystem. Hierarchical Bayesian modelling was used to construct phylogenies and estimate divergence times. We developed species distribution models to determine what climatic variables and soil parameters predicted species presence by comparing the current to the historic and predicted future distribution of the species. Finally, we explore the impact of environmental variables on the genetic structure of Ctenomys based on current and past species distributions. The variables that consistently correlated with the predicted distribution of the species and explained the observed genetic differentiation among populations included the distribution of well-drained sandy soils and temperature seasonality. A core region of stable suitable habitat was identified from the Last Interglacial, which is projected to remain stable into the future. This region is also the most genetically diverse and is currently under strong anthropogenic pressure. Results reveal complex demographic dynamics, which have been in constant change in both time and space, and are likely linked to the evolution of the Paraná River. We suggest that any alteration of soil properties (climatic or anthropic) may significantly impact the availability of suitable habitat and consequently the ability of individuals to disperse. The protection of this core stable habitat is of prime importance given the increasing levels of human disturbance across this wetland system and the threat of climate change.
Subject(s)
Environment , Rodentia/genetics , Animals , DNA, Mitochondrial/genetics , Genetic Variation , Models, Statistical , PhylogenyABSTRACT
The chromosomal speciation hypothesis suggests that irregularities in synapsis, recombination, and segregation in heterozygotes for chromosome rearrangements may restrict gene flow between karyotypically distinct populations and promote speciation. Ctenomys talarum is a South American subterranean rodent inhabiting the coastal regions of Argentina, whose populations polymorphic for Robertsonian and tandem translocations seem to have a very restricted gene flow. To test if chromosomal differences are involved in isolation among its populations, we examined chromosome pairing, recombination, and meiotic silencing of unsynapsed chromatin in male meiosis of simple and complex translocation heterozygotes using immunolocalization of the MLH1 marking mature recombination nodules and phosphorylated histone γH2A.X marking unrepaired double-strand breaks. We observed small asynaptic areas labeled by γH2A.X in pericentromeric regions of the chromosomes involved in the trivalents and quadrivalents. We also observed a decrease of recombination frequency and a distalization of the crossover distribution in the heterozygotes and metacentric homozygotes compared to acrocentric homozygotes. We suggest that the asynapsis of the pericentromeric regions are unlikely to induce germ cell death and decrease fertility of the heterozygotes; however, suppressed recombination in pericentromeric areas of the multivalents may reduce gene flow between chromosomally different populations of the Talas tuco-tuco.
Subject(s)
Chromosome Pairing/genetics , Chromosomes, Mammalian/genetics , Recombination, Genetic , Rodentia/genetics , Animals , Heterozygote , Histones/metabolism , Male , Nuclear Proteins/metabolism , Spermatocytes/metabolismABSTRACT
Delimiting species is very conflicting in the case of very young taxa that are in the process of diversification, and even more difficult if the species inhabit a heterogeneous environment. In this case, even population delimitation is controversial. The South American genus of subterranean rodents Ctenomys is highly speciose, with 62 species that appeared in the lapse of 3 Myr. Within the genus, the 'perrensi' group, formed by three named species and a group of forms of unknown taxonomic status, inhabits the Iberá wetland, in northern Argentina. Almost every locality shows a particular chromosomal complement. To understand the relationships and the evolutionary process among species and populations, we examined mitochondrial DNA sequences and microsatellite genotypes. We found an isolation-by-distance pattern with evidence of cluster-like behaviour of the system. The mitochondrial DNA network revealed two different groups, separated by one of the main rivers of the region. Clustering methods delimited 12 different populations and five metapopulation lineages that seem to be evolving independently. We found evidence of ancient migration among localities at the centre of the distribution but no signals of current migration among the 12 delimited clusters. Some of the genetic clusters found included localities with different chromosomal numbers, which points to the existence of gene flow despite chromosomal variation. The evolutionary future of these five lineages is controlled by the dynamics of their habitat: if stable, they may become distinct species; otherwise, they may collapse into a hybrid swarm, forming a single evolving metapopulation.
Subject(s)
Genetic Speciation , Phylogeography , Rodentia/genetics , Animals , Argentina , Cluster Analysis , DNA, Mitochondrial/genetics , Gene Flow , Genetic Variation , Genotype , Microsatellite Repeats , Rodentia/classification , Sequence Analysis, DNAABSTRACT
El objetivo del trabajo es evaluar en forma retrospectiva la utilización de la TC para diagnóstico de TEP en un hospital privado e identificar su verdadera utilidad y correcta indicación ante tal sospecha diagnóstica.
Subject(s)
Humans , Pulmonary Embolism/diagnosis , Pulmonary Embolism/pathology , Pulmonary Embolism , Pulmonary Embolism/therapy , Tomography, Spiral ComputedABSTRACT
La utilización de la tomografía helicoidal en el diagnóstico de tromboembolismo pulmonar, data de más de una década. Desde entonces múltiples estudios han intentado definir su utilidad y a pesar de la falta de protocolos correctamente diseñados, esta metodología está ganando rápidamente aceptación como primer estudio a solicitar ante la sospecha de TEP. El objetivo del trabajo es evaluar en forma retrospectiva la utilización de la TC para diagnóstico de TEP en un hospital privado e identificar suverdadera utilidad y correcta indicación ante tal sospecha diagnóstica
Subject(s)
Humans , Angiography , Medical Records , Pulmonary Embolism , Tomography, Spiral Computed , Ventilation-Perfusion RatioABSTRACT
La utilización de la tomografía helicoidal en el diagnóstico de tromboembolismo pulmonar, data de más de una década. Desde entonces múltiples estudios han intentado definir su utilidad y a pesar de la falta de protocolos correctamente diseñados, esta metodología está ganando rápidamente aceptación como primer estudio a solicitar ante la sospecha de TEP. El objetivo del trabajo es evaluar en forma retrospectiva la utilización de la TC para diagnóstico de TEP en un hospital privado e identificar suverdadera utilidad y correcta indicación ante tal sospecha diagnóstica
