Investigation of the relationships between basin morphology, tectonic uplift, and denudation from the study of an active fold belt in the Siwalik Hills, central Nepal

The present study investigates correlations between an extensive range of geomorphic properties that can be estimated from a digital elevation model and the uplift rate on geological timescales. The analysis focuses on an area in the Siwalik Hills (central Nepal), where lithology and climate can be considered as uniform. This area undergoes rapid tectonic uplift at rates of up to 15 mm yr^(−1), which are derived from the geometric pattern of a fault-bend model of fold growth. The selected geomorphic properties can be divided in two categories, depending on whether or not the vertical dimension is taken into account. None of the planar properties are significantly correlated to uplift rate, unlike those that include the vertical dimension, such as the mean elevation of basins, hypsometric curve, and hypsometric integral, and relief defined by the amplitude factor of length scaling analysis. Correlation between relief and uplift rate is observed for all length scales of topography shorter than 600 m, which suggests that all orders of the streams are able to adjust to the tectonic signal. Simple mass balance considerations imply that the average elevation is only 10% of surface uplift, suggesting that a dynamic equilibrium has been reached quite rapidly. Using a simple two-process model for erosion, we find that fairly high diffusion coefficients (order of 10 m^2 yr^(−1)) and efficient transport of the material by rivers are required. This unusually high value for mass diffusivity at small length scales may be obtained by either a very efficient linear diffusion or by landsliding. Actually, both processes may be active, which appears likely given the nature of the unconsolidated substratum and the favorable climatic conditions. Local relief in the study area may therefore be used to predict either uplift or denudation, but the prediction is calibrated only for that specific climatic and lithologic conditions and cannot be systematically applied to other contexts

Self-fertilization, long-distance flash invasion andbiogeography shape the population structure ofPseudosuccinea columella at the worldwide scale

International audiencePopulation genetic studies are efficient for inferring the invasion history based on acomparison of native and invasive populations, especially when conducted at speciesscale. An expected outcome in invasive populations is variability loss, and this is especiallytrue in self-fertilizing species. We here focus on the self-fertilizing Pseudosuccineacolumella, an invasive hermaphroditic freshwater snail that has greatly expandedits geographic distribution and that acts as intermediate host of Fasciola hepatica, thecausative agent of human and veterinary fasciolosis. We evaluated the distribution ofgenetic diversity at the largest geographic scale analysed to date in this species by surveying80 populations collected during 16 years from 14 countries, using eight nuclearmicrosatellites and two mitochondrial genes. As expected, populations from NorthAmerica, the putative origin area, were strongly structured by selfing and history andharboured much more genetic variability than invasive populations. We found highselfing rates (when it was possible to infer it), none-to-low genetic variability andstrong population structure in most invasive populations. Strikingly, we found aunique genotype/haplotype in populations from eight invaded regions sampled allover the world. Moreover, snail populations resistant to infection by the parasite aregenetically distinct from susceptible populations. Our results are compatible withrepeated introductions in South America and flash worldwide invasion by this uniquegenotype/haplotype. Our study illustrates the population genetic consequences of bio-logical invasion in a highly selfing species at very large geographic scale. We discusshow such a large-scale flash invasion may affect the spread of fasciolosi