Greenhouse gas emissions in Sub-Saharan Africa

Current and future carbon emissions from land-use change and energy consumption were analyzed for Sub-Saharan Africa. The energy sector analysis was based on UN energy data tapes while the land-use analysis was based on a spatially-explicit land-use model developed specifically for this project. The impacts of different energy and land-use strategies on future carbon emissions were considered. (A review of anthropogenic emissions of methane, nitrous oxides, and chlorofluorocarbons in Sub-Saharan Africa indicated that they were probably minor in both a global and a regional context. The study therefore was focused on emissions of carbon dioxide.) The land-use model predicts carbon emissions from land use change and the amount of carbon stored in vegetation (carbon inventory) on a yearly basis between 1985 and 2001. Emissions and inventory are modeled at 9000 regularly-spaced point locations in Sub-Saharan Africa using location-specific information on vegetation type, soils, climate and deforestation. Vegetation, soils, and climate information were derived from continental-scale maps while relative deforestation rates(% of forest land lost each year) were developed from country-specific forest and deforestation statistics (FAO Tropical Forest Resources Assessment for Africa, 1980). The carbon emissions under different land use strategies in Sub-Saharan Africa were analyzed by modifying deforestation rates and altering the amount of carbon stored under different land uses. The considered strategies were: preservation of existing forests, implementation of agroforestry, and establishment of industrial tree plantations. 82 refs., 16 figs., 25 tabs

Quantitative Evidence for the Effects of Multiple Drivers on Continental-Scale Amphibian Declines

Since amphibian declines were first proposed as a global phenomenon over a quarter century ago, the conservation community has made little progress in halting or reversing these trends. The early search for a “smoking gun” was replaced with the expectation that declines are caused by multiple drivers. While field observations and experiments have identified factors leading to increased local extinction risk, evidence for effects of these drivers is lacking at large spatial scales. Here, we use observations of 389 time-series of 83 species and complexes from 61 study areas across North America to test the effects of 4 of the major hypothesized drivers of declines. While we find that local amphibian populations are being lost from metapopulations at an average rate of 3.79% per year, these declines are not related to any particular threat at the continental scale; likewise the effect of each stressor is variable at regional scales. This result - that exposure to threats varies spatially, and populations vary in their response - provides little generality in the development of conservation strategies. Greater emphasis on local solutions to this globally shared phenomenon is needed

Quantitative Evidence for the Effects of Multiple Drivers on Continental-Scale Amphibian Declines

Since amphibian declines were first proposed as a global phenomenon over a quarter century ago, the conservation community has made little progress in halting or reversing these trends. The early search for a “smoking gun” was replaced with the expectation that declines are caused by multiple drivers. While field observations and experiments have identified factors leading to increased local extinction risk, evidence for effects of these drivers is lacking at large spatial scales. Here, we use observations of 389 time-series of 83 species and complexes from 61 study areas across North America to test the effects of 4 of the major hypothesized drivers of declines. While we find that local amphibian populations are being lost from metapopulations at an average rate of 3.79% per year, these declines are not related to any particular threat at the continental scale; likewise the effect of each stressor is variable at regional scales. This result - that exposure to threats varies spatially, and populations vary in their response - provides little generality in the development of conservation strategies. Greater emphasis on local solutions to this globally shared phenomenon is needed

Large-Scale Selective Sweep among Segregation Distorter Chromosomes in African Populations of Drosophila melanogaster

Segregation Distorter (SD) is a selfish, coadapted gene complex on chromosome 2 of Drosophila melanogaster that strongly distorts Mendelian transmission; heterozygous SD/SD+ males sire almost exclusively SD-bearing progeny. Fifty years of genetic, molecular, and theory work have made SD one of the best-characterized meiotic drive systems, but surprisingly the details of its evolutionary origins and population dynamics remain unclear. Earlier analyses suggested that the SD system arose recently in the Mediterranean basin and then spread to a low, stable equilibrium frequency (1–5%) in most natural populations worldwide. In this report, we show, first, that SD chromosomes occur in populations in sub-Saharan Africa, the ancestral range of D. melanogaster, at a similarly low frequency (∼2%), providing evidence for the robustness of its equilibrium frequency but raising doubts about the Mediterranean-origins hypothesis. Second, our genetic analyses reveal two kinds of SD chromosomes in Africa: inversion-free SD chromosomes with little or no transmission advantage; and an African-endemic inversion-bearing SD chromosome, SD-Mal, with a perfect transmission advantage. Third, our population genetic analyses show that SD-Mal chromosomes swept across the African continent very recently, causing linkage disequilibrium and an absence of variability over 39% of the length of the second chromosome. Thus, despite a seemingly stable equilibrium frequency, SD chromosomes continue to evolve, to compete with one another, or evade suppressors in the genome

Very High Order Masking: Efficient Implementation and Security Evaluation

In this paper, we study the performances and security of recent masking algorithms specialized to parallel implementations in a 32-bit embedded software platform, for the standard AES Rijndael and the bitslice cipher Fantomas. By exploiting the excellent features of these algorithms for bitslice implementations, we first extend the recent speed records of Goudarzi and Rivain (presented at Eurocrypt 2017) and report realistic timings for masked implementations with 32 shares. We then observe that the security level provided by such implementations is uneasy to quantify with current evaluation tools. We therefore propose a new ``multi-model evaluation methodology which takes advantage of different (more or less abstract) security models introduced in the literature. This methodology allows us to both bound the security level of our implementations in a principled manner and to assess the risks of overstated security based on well understood parameters. Concretely, it leads us to conclude that these implementations withstand worst-case adversaries with >2^64 measurements under falsifiable assumptions

Epigenomic and functional analyses reveal roles of epialleles in the loss of photoperiod sensitivity during domestication of allotetraploid cottons

Abstract Background Polyploidy is a pervasive evolutionary feature of all flowering plants and some animals, leading to genetic and epigenetic changes that affect gene expression and morphology. DNA methylation changes can produce meiotically stable epialleles, which are transmissible through selection and breeding. However, the relationship between DNA methylation and polyploid plant domestication remains elusive. Results We report comprehensive epigenomic and functional analyses, including ~12 million differentially methylated cytosines in domesticated allotetraploid cottons and their tetraploid and diploid relatives. Methylated genes evolve faster than unmethylated genes; DNA methylation changes between homoeologous loci are associated with homoeolog-expression bias in the allotetraploids. Significantly, methylation changes induced in the interspecific hybrids are largely maintained in the allotetraploids. Among 519 differentially methylated genes identified between wild and cultivated cottons, some contribute to domestication traits, including flowering time and seed dormancy. CONSTANS (CO) and CO-LIKE (COL) genes regulate photoperiodicity in Arabidopsis. COL2 is an epiallele in allotetraploid cottons. COL2A is hypermethylated and silenced, while COL2D is repressed in wild cottons but highly expressed due to methylation loss in all domesticated cottons tested. Inhibiting DNA methylation activates COL2 expression, and repressing COL2 in cultivated cotton delays flowering. Conclusions We uncover epigenomic signatures of domestication traits during cotton evolution. Demethylation of COL2 increases its expression, inducing photoperiodic flowering, which could have contributed to the suitability of cotton for cultivation worldwide. These resources should facilitate epigenetic engineering, breeding, and improvement of polyploid crops