| 1. |
- Breton, Gwenna
(författare)
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Human demographic history : Insights on the human past based on genomes from Southern through Central Africa
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Evidence from paleontology, archaeology and population genetics support that modern humans originated in Africa. While the out-of-Africa event and subsequent colonization of all continents are well documented, human history in Africa at that time and before is less studied. Some current-day hunter-gatherer populations trace most of their genetic lineages to populations who inhabited Sub-Saharan Africa until the arrival of farming. They are informative about human history before and after the arrival of farming.I studied high-coverage genomes from two such groups, the Khoe-San from Southern Africa and the rainforest hunter-gatherers from Central Africa. I generated a total of 74 genomes, significantly increasing the number of genomes from Sub-Saharan African hunter-gatherers. I compared several versions of a commonly used pipeline for high-coverage genomes and showed that using standard ascertained reference datasets has no significant impact on variant calling in populations from Sub-Saharan Africa. Using the full genome information, I described the genetic diversity in the Khoe-San and in the rainforest hunter-gatherers and showed that gene flow from agropastoralist groups increased the Khoe-San genetic diversity. I also detected a signal of population size decline in the Khoe-San around the time of the out-of-Africa event, and I evaluated the power of the method to detect bottlenecks by applying it to simulated data. I investigated the history of modern humans in Africa by estimating divergence times between populations and applying an Approximate Bayesian Computation analysis. We confirmed that the earliest divergence event was between the Khoe-San ancestral lineage and the rest of modern humans, ~250-350 kya. I also showed that the possibility of high gene flow should be incorporated in models of human evolution.I furthermore examined SNP array data for two BaTwa populations from Zambia and showed that 20-30% of their autosomal diversity is hunter-gatherer-like. The estimated times for the admixture between a presumably local hunter-gatherer population and incoming agropastoralist groups are consistent with archaeological records.In this thesis, I investigated questions related to human history in Sub-Saharan Africa, from the emergence of modern humans ~300 kya to recent events related to the expansion of farming.
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| 2. |
- Sjöstrand, Agnès E.
(författare)
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Origins and Adaptation in Humans : A Case Study of Taste and Lifestyle
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, I use population genetics and statistical approaches to investigate early human demography, infer local adaptation in diverse sets of populations, and study the genetic basis for taste perception.In the first paper, I examine the genomic evidence for a severe bottleneck, which has been suggested based on paleontological and climate studies to coincide with the emergence of anatomically modern humans. Using a Bayesian approach, I evaluate the genetic evidence of a bottleneck between 190,000 and 130,000 years ago and find that the data is in favor of a model without bottleneck at this time point.I further develop a method to detect local adaptation based on frequencies of private haplotypes. I first show, using simulated data, that this method can detect local adaption. Applied to large-scale human genotype data, this method detects known signals of positive selection in human data such as the positive selection around the lactase gene in Europeans and East Africans. Also, this method permits to improve knowledge on potential adaptation events in humans as it finds several regions potentially selected that were not previously described. I further investigate patterns of adaptation in whole genome data based on a diverse set of African populations. The results from the regions potentially selected show that diet and pathogens are the common driving forces of adaptation in all studied populations.There is evidence that taste perception have evolved in concert with diet, environment, and the organismal needs in humans. For this reason, I study taste perception in populations differing on lifestyle (hunter-gatherers, farmers and nomad herders). I present taste perception phenotypes for all tastes (sweet, bitter, sour, salty and umami) and relate them to high density genotype data. I show that taste and taste-involved genes have evolved with lifestyle. By performing an association study, I also show that variation in taste perception involves more genes than only the taste receptors genes.In this thesis, by analyzing human genetic data with a population genetics approaches, I covered several topics of human ancient demography and adaptation and show the utility of using large-scale genetic data to better understand human history.
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| 3. |
- Vandaele, Ann Carine, et al.
(författare)
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Martian dust storm impact on atmospheric H2O and D/H observed by ExoMars Trace Gas Orbiter
- 2019
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Ingår i: Nature. - : Springer. - 1476-4687 .- 1476-4687 .- 0028-0836. ; 568:7753, s. 521-525
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Global dust storms on Mars are rare1,2 but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere3, primarily owing to solar heating of the dust3. In turn, changes in atmospheric dynamics can affect the distribution of atmospheric water vapour, with potential implications for the atmospheric photochemistry and climate on Mars4. Recent observations of the water vapour abundance in the Martian atmosphere during dust storm conditions revealed a high-altitude increase in atmospheric water vapour that was more pronounced at high northern latitudes5,6, as well as a decrease in the water column at low latitudes7,8. Here we present concurrent, high-resolution measurements of dust, water and semiheavy water (HDO) at the onset of a global dust storm, obtained by the NOMAD and ACS instruments onboard the ExoMars Trace Gas Orbiter. We report the vertical distribution of the HDO/H2O ratio (D/H) from the planetary boundary layer up to an altitude of 80 kilometres. Our findings suggest that before the onset of the dust storm, HDO abundances were reduced to levels below detectability at altitudes above 40 kilometres. This decrease in HDO coincided with the presence of water-ice clouds. During the storm, an increase in the abundance of H2O and HDO was observed at altitudes between 40 and 80 kilometres. We propose that these increased abundances may be the result of warmer temperatures during the dust storm causing stronger atmospheric circulation and preventing ice cloud formation, which may confine water vapour to lower altitudes through gravitational fall and subsequent sublimation of ice crystals3. The observed changes in H2O and HDO abundance occurred within a few days during the development of the dust storm, suggesting a fast impact of dust storms on the Martian atmosphere.
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