261 research outputs found
THE USE OF SIMULATIONS IN EVOLUTIONARY POPULATION GENETICS: APPLICATIONS ON HUMANS, OWLS AND VIRTUAL ORGANISMS
Summary (in English)
Computer simulations provide a practical way to address scientific questions that would be otherwise intractable. In evolutionary biology, and in population genetics in particular, the investigation of evolutionary processes frequently involves the implementation of complex models, making simulations a particularly valuable tool in the area. In this thesis work, I explored three questions involving the geographical range expansion of populations, taking advantage of spatially explicit simulations coupled with approximate Bayesian computation. First, the neutral evolutionary history of the human spread around the world was investigated, leading to a surprisingly simple model: A straightforward diffusion process of migrations from east Africa throughout a world map with homogeneous landmasses replicated to very large extent the complex patterns observed in real human populations, suggesting a more continuous (as opposed to structured) view of the distribution of modern human genetic diversity, which may play a better role as a base model for further studies. Second, the postglacial evolution of the European barn owl, with the formation of a remarkable coat-color cline, was inspected with two rounds of simulations: (i) determine the demographic background history and (ii) test the probability of a phenotypic cline, like the one observed in the natural populations, to appear without natural selection. We verified that the modern barn owl population originated from a single Iberian refugium and that they formed their color cline, not due to neutral evolution, but with the necessary participation of selection. The third and last part of this thesis refers to a simulation-only study inspired by the barn owl case above. In this chapter, we showed that selection is, indeed, effective during range expansions and that it leaves a distinguished signature, which can then be used to detect and measure natural selection in range-expanding populations.
ReĢsumeĢ (en francĢ§ais)
Les simulations fournissent un moyen pratique pour reĢpondre aĢ des questions scientifiques qui seraient inabordable autrement. En geĢneĢtique des populations, l'eĢtude des processus eĢvolutifs implique souvent la mise en oeuvre de modeĢles complexes, et les simulations sont un outil particulieĢrement preĢcieux dans ce domaine. Dans cette theĢse, j'ai exploreĢ trois questions en utilisant des simulations spatialement explicites dans un cadre de calculs BayeĢsiens approximeĢs (approximate Bayesian computation : ABC). Tout d'abord, l'histoire de la colonisation humaine mondiale et de l'eĢvolution de parties neutres du geĢnome a eĢteĢ eĢtudieĢe graĢce aĢ un modeĢle eĢtonnement simple. Un processus de diffusion des migrants de l'Afrique orientale aĢ travers un monde avec des masses terrestres homogeĢnes a reproduit, dans une treĢs large mesure, les signatures geĢneĢtiques complexes observeĢes dans les populations humaines reĢelles. Un tel modeĢle continu (opposeĢ aĢ un modeĢle structureĢ en populations) pourrait eĢtre treĢs utile comme modeĢle de base dans l'eĢtude de geĢneĢtique humaine aĢ l'avenir. DeuxieĢmement, l'eĢvolution postglaciaire d'un gradient de couleur chez l'Effraie des clocher (Tyto alba) EuropeĢenne, a eĢteĢ examineĢ avec deux seĢries de simulations pour : (i) deĢterminer l'histoire deĢmographique de base et (ii) tester la probabiliteĢ qu'un gradient pheĢnotypique, tel qu'observeĢ dans les populations naturelles puisse apparaiĢtre sans seĢlection naturelle. Nous avons montreĢ que la population actuelle des chouettes est sortie d'un unique refuge ibeĢrique et que le gradient de couleur ne peux pas s'eĢtre formeĢ de manieĢre neutre (sans l'action de la seĢlection naturelle). La troisieĢme partie de cette theĢse se reĢfeĢre aĢ une eĢtude par simulations inspireĢe par l'eĢtude de l'Effraie. Dans ce dernier chapitre, nous avons montreĢ que la seĢlection est, en effet, aussi efficace dans les cas d'expansion d'aire de distribution et qu'elle laisse une signature unique, qui peut eĢtre utiliseĢe pour la deĢtecter et estimer sa force
Impurity intrusion in radio-frequency micro-plasma jets operated in ambient air
Space and time resolved concentrations of helium metastable atoms in an
atmospheric pressure radio-frequency micro-plasma jet were measured using
tunable diode laser absorption spectroscopy. Spatial profiles as well as
lifetime measurements show significant influences of air entering the discharge
from the front nozzle and of impurities originating from the gas supply system.
Quenching of metastables was used to deduce quantitative concentrations of
intruding impurities. The impurity profile along the jet axis was determined
from optical emission spectroscopy as well as their dependance on the feed gas
flow through the jet.Comment: Journal of Physics D: Applied Physics (accepted), 6 page
A Reevaluation of the Native American MtDNA Genome Diversity and Its Bearing on the Models of Early Colonization of Beringia
The Americas were the last continents to be populated by humans, and their colonization represents a very interesting chapter in our species' evolution in which important issues are still contentious or largely unknown. One difficult topic concerns the details of the early peopling of Beringia, such as for how long it was colonized before people moved into the Americas and the demography of this occupation. A recent work using mitochondrial genome (mtDNA) data presented evidence for a so called āthree-stage modelā consisting of a very early expansion into Beringia followed by ā¼20,000 years of population stability before the final entry into the Americas. However, these results are in disagreement with other recent studies using similar data and methods. Here, we reanalyze their data to check the robustness of this model and test the ability of Native American mtDNA to discriminate details of the early colonization of Beringia. We apply the Bayesian Skyline Plot approach to recover the past demographic dynamic underpinning these events using different mtDNA data sets. Our results refute the specific details of the āthree-stage modelā, since the early stage of expansion into Beringia followed by a long period of stasis could not be reproduced in any mtDNA data set cleaned from non-Native American haplotypes. Nevertheless, they are consistent with a moderate population bottleneck in Beringia associated with the Last Glacial Maximum followed by a strong population growth around 18,000 years ago as suggested by other recent studies. We suggest that this bottleneck erased the signals of ancient demographic history from recent Native American mtDNA pool, and conclude that the proposed early expansion and occupation of Beringia is an artifact caused by the misincorporation of non-Native American haplotypes
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Radiative effect of aerosols above the northern and southern Atlantic Ocean as determined from shipborne lidar observations
The direct solar radiative effect of aerosols over the Atlantic Ocean was investigated on the basis of aerosol Raman/polarization lidar observations aboard the research vessel Polarsternbetween Germany (50Ā°N) and either South America (50Ā°S) or South Africa (40Ā°S) in 2009 and 2010. First, a case study of complex aerosol conditions with marine aerosol, dust, and smoke particles in the boundary layer and free troposphere is presented to demonstrate that detailed knowledge of aerosol layering (boundary layer, free troposphere) and aerosol mixing state is required for an accurate determination of the resulting radiative effects. A statistical analysis based on all lidar observations revealed the highest daily mean radiative effect (ā43Ā±59āWāmā2at the surface, ā14Ā±18āWāmā2at top of atmosphere) in the latitudinal belt from 0Ā°Nā15Ā°N in the Saharan dust outflow region. Mean aerosol radiative effects of the polluted northern and clean southern midlatitudes were contrasted. In the northern midlatitudes, the averaged aerosol radiative effect of all simulations was ā24Ā±33āWāmā2at the surface which is a factor of 1.6 higher than at similar southern hemispheric latitudes. The simulations based on the lidar observations are in good agreement with colocated pyranometer measurements
Profiling of Saharan dust from the Caribbean to western Africa - Part 1: Layering structures and optical properties from shipborne polarization/Raman lidar observations
We present final and quality-assured results of multiwavelength polarization/Raman lidar observations of the Saharan air layer (SAL) over the tropical Atlantic. Observations were performed aboard the German research vessel R/V Meteor during the 1-month transatlantic cruise from Guadeloupe to Cabo Verde over 4500 km from 61.5 to 20 degrees W at 14-15 degrees N in April-May 2013. First results of the ship-borne lidar measurements, conducted in the framework of SALTRACE (Saharan Aerosol Long-range Transport and Aerosol-Cloud Interaction Experiment), were reported by Kanitz et al. (2014). Here, we present four observational cases representing key stages of the SAL evolution between Africa and the Caribbean in detail in terms of layering structures and optical properties of the mixture of predominantly dust and aged smoke in the SAL. We discuss to what extent the lidar results confirm the validity of the SAL conceptual model which describes the dust long-range transport and removal processes over the tropical Atlantic. Our observations of a clean marine aerosol layer (MAL, layer from the surface to the SAL base) confirm the conceptual model and suggest that the removal of dust from the MAL, below the SAL, is very efficient. However, the removal of dust from the SAL assumed in the conceptual model to be caused by gravitational settling in combination with large-scale subsidence is weaker than expected. To explain the observed homogenous (height-independent) dust optical properties from the SAL base to the SAL top, from the African coast to the Caribbean, we have to assume that the particle sedimentation strength is reduced and dust vertical mixing and upward transport mechanisms must be active in the SAL. Based on lidar observations on 20 nights at different longitudes in May 2013, we found, on average, MAL and SAL layer mean values (at 532 nm) of the extinction-to-backscatter ratio (lidar ratio) of 17 +/- 5 sr (MAL) and 43 +/- 8 sr (SAL), of the particle linear depolarization ratio of 0.025 +/- 0 : 015 (MAL) and 0.19 +/- 0.09 (SAL), and of the particle extinction coefficient of 67 +/- 45Mm(-1) (MAL) and 68 +/- 37Mm(-1) (SAL). The 532 nm optical depth of the lofted SAL was found to be, on average, 0.15 +/- 0.13 during the ship cruise. The comparably low values of the SAL mean lidar ratio and depolarization ratio (compared to typical pure dust values of 50-60 sr and 0.3, respectively) in combination with backward trajectories indicate a smoke contribution to light extinction of the order of 20% during May 2013, at the end of the burning season in central-western Africa
Surface matters: Limitations of CALIPSO V3 aerosol typing in coastal regions
In the CALIPSO data analysis, surface type (land/ocean) is used to augment the aerosol characterization. However, this surface-dependent aerosol typing prohibits a correct classification of marine aerosol over land that is advected from ocean to land. This might result in a systematic overestimation of the particle extinction coefficient and of the aerosol optical thickness (AOT) of up to a factor of 3.5 over land in coastal areas. We present a long-term comparison of CALIPSO and ground-based lidar observations of the aerosol conditions in the coastal environment of southern South America (Punta Arenas, Chile, 53Ā° S), performed in December 2009āApril 2010. Punta Arenas is almost entirely influenced by marine particles throughout the year, indicated by a rather low AOT of 0.02ā0.04. However, we found an unexpectedly high fraction of continental aerosol in the aerosol types inferred by means of CALIOP observations and, correspondingly, too high values of particle extinction. Similar features of the CALIOP data analysis are presented for four other coastal areas around the world. Since CALIOP data serve as important input for global climate models, the influence of this systematic error was estimated by means of simplified radiative-transfer calculations
Mobilizing professorsā support of digital change: Multi-level insights on IT resources as a boundary condition
The success of top-down digital change initiatives in higher education institutions (HEIs) largely depends on the support of professors as change recipients and catalysts within their departments. For effectively managing change, a better understanding of how process factors under management control (i.e., vision communication, change facilitation, participation opportunities, change coordination) simultaneously relate to professorsā cognitive and behavioral change support is crucial. Moreover, we examine how department-level IT
resources as a context factor shape process-reaction relationships. Based on data from 1,400 professors nested in 258 departments within German HEIs, multilevel regression analyses support the relevance of vision communication, change facilitation, and participation opportunities ā but not of change coordination. As department-level IT resources increase, vision communication more strongly relates to cognitive change support, pointing to unexplored higher-level boundary conditions of vision communication. Our study advances
knowledge about mobilizing change support and managing top-down change with limited top-down influence to impose change
An overview of the first decade of PollyNET : an emerging network of automated Raman-polarization lidars for continuous aerosol profiling
Ā© Author(s) 2016. This work is distributed under the Creative Commons Attribution 3.0 LicenseA global vertically resolved aerosol data set covering more than 10 years of observations at more than 20 measurement sites distributed from 63Ā°āÆN to 52Ā°āÆS and 72Ā°āÆW to 124Ā°āÆE has been achieved within the Raman and polarization lidar network PollyNET. This network consists of portable, remote-controlled multiwavelength-polarization-Raman lidars (Polly) for automated and continuous 24/7 observations of clouds and aerosols. PollyNET is an independent, voluntary, and scientific network. All Polly lidars feature a standardized instrument design with different capabilities ranging from single wavelength to multiwavelength systems, and now apply unified calibration, quality control, and data analysis. The observations are processed in near-real time without manual intervention, and are presented online at http://polly.tropos.de/. The paper gives an overview of the observations on four continents and two research vessels obtained with eight Polly systems. The specific aerosol types at these locations (mineral dust, smoke, dust-smoke and other dusty mixtures, urban haze, and volcanic ash) are identified by their Ć
ngstrƶm exponent, lidar ratio, and depolarization ratio. The vertical aerosol distribution at the PollyNET locations is discussed on the basis of more than 55āÆ000 automatically retrieved 30āÆmin particle backscatter coefficient profiles at 532āÆnm as this operating wavelength is available for all Polly lidar systems. A seasonal analysis of measurements at selected sites revealed typical and extraordinary aerosol conditions as well as seasonal differences. These studies show the potential of PollyNET to support the establishment of a global aerosol climatology that covers the entire troposphere.Peer reviewe
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