Approachability in Stackelberg Stochastic Games with Vector Costs

The notion of approachability was introduced by Blackwell [1] in the context of vector-valued repeated games. The famous Blackwell's approachability theorem prescribes a strategy for approachability, i.e., for `steering' the average cost of a given agent towards a given target set, irrespective of the strategies of the other agents. In this paper, motivated by the multi-objective optimization/decision making problems in dynamically changing environments, we address the approachability problem in Stackelberg stochastic games with vector valued cost functions. We make two main contributions. Firstly, we give a simple and computationally tractable strategy for approachability for Stackelberg stochastic games along the lines of Blackwell's. Secondly, we give a reinforcement learning algorithm for learning the approachable strategy when the transition kernel is unknown. We also recover as a by-product Blackwell's necessary and sufficient condition for approachability for convex sets in this set up and thus a complete characterization. We also give sufficient conditions for non-convex sets.Comment: 18 Pages, Submitted to Dynamic Games and Application

Simulated future conditions of ocean warming and acidification disrupt the microbiome of the calcifying foraminifera Marginopora vertebralis across life stages

Foraminifera host diverse microbial communities that can shift in response to changing environmental conditions. To characterize climate change impacts on the foraminifera microbiome across life stages, we exposed adult\ua0Marginopora vertebralis\ua0(Large Benthic Foraminifera) to\ua0pCO2\ua0and temperature scenarios representing present day, 2050 and 2100 levels and raised juveniles under present day and 2050 conditions. While treatment condition had no significant effect on the seawater microbial communities, exposure to future scenarios significantly altered both adult and juvenile microbiomes. In adults, divergence between present day and 2050 or 2100 conditions was primarily driven by a reduced relative abundance of Oxyphotobacteria under elevated temperature and\ua0pCO2. In juveniles, the microbial shift predominantly resulted from changes in the proportion of Proteobacteria. Indicator species analysis identified numerous treatment‐specific indicator taxa, most of which were indicative of present day conditions. Oxyphotobacteria, previously reported as putative symbionts of foraminifera, were indicative of present day and 2050 conditions in adults, but of present day conditions only in juveniles. Overall, we show that the sensitivity of the\ua0M. vertebralis\ua0microbiome to climate change scenarios extends to both life stages and primarily correlates with declines in Oxyphotobacteria and shifts in Proteobacteria under elevated temperature and\ua0pCO2

A genomic view of the microbiome of coral reef demosponges

Sponges underpin the productivity of coral reefs, yet few of their microbial symbionts have been functionally characterised. Here we present an analysis of ~1200 metagenome-assembled genomes (MAGs) spanning seven sponge species and 25 microbial phyla. Compared to MAGs derived from reef seawater, sponge-associated MAGs were enriched in glycosyl hydrolases targeting components of sponge tissue, coral mucus and macroalgae, revealing a critical role for sponge symbionts in cycling reef organic matter. Further, visualisation of the distribution of these genes amongst symbiont taxa uncovered functional guilds for reef organic matter degradation. Genes for the utilisation of sialic acids and glycosaminoglycans present in sponge tissue were found in specific microbial lineages that also encoded genes for attachment to sponge-derived fibronectins and cadherins, suggesting these lineages can utilise specific structural elements of sponge tissue. Further, genes encoding CRISPR and restriction-modification systems used in defence against mobile genetic elements were enriched in sponge symbionts, along with eukaryote-like gene motifs thought to be involved in maintaining host association. Finally, we provide evidence that many of these sponge-enriched genes are laterally transferred between microbial taxa, suggesting they confer a selective advantage within the sponge niche and therefore play a critical role in host ecology and evolution

Learning Letters with the Whole Body: Visuo-Motor versus Visual Teaching in Kindergarten

International audienceIn early school years, children must learn letters; what constitutes effective teaching is still uncertain. In this study, we assessed the impact of a teacher-implemented visuo-motor intervention program to teach 5-year-olds' cursive letter knowledge. We compared a program in which letters were explored with the arm and whole body, with a typical visual training program. Children were tested before and after the intervention with different measures of letter knowledge. We showed a greater improvement in letter recognition following the visuo-motor intervention, compared to the visual intervention. Results were mixed for letter handwriting: higher scores on stroke direction and overall quality, but lower scores on fluency following visuo-motor teaching. We discuss these results in terms of the link between action and perception, the interaction between the different components of letter knowledge, and the link between fine and gross motor development and handwriting

Perception of the cursive handwriting movement in writers and pre-writers

International audienceThe objective of this study was to confirm the existence of knowledge relating to the cursive writing movement for French pupils in 3rd year of kindergarten, 2nd grade and 5th grade of elementary school. 141 pupils were asked to watch a visual presentation of cursive handwriting to determine whether they were able to detect violations of two rules of handwriting: continuity and sequentiality of the cursive handwriting movement. Our results showed progressive development of the understanding of characteristics of the cursive handwriting movement, with different developmental trajectories of knowledge for the different rules. The ability to detect continuity of the cursive writing movement developed earlier than the ability to detect sequentiality. Correct decisions were not always accompanied by correct justifications, which developed more slowly than detection of rule violations

Complex Endosymbioses II: The Nonphotosynthetic Plastid of Apicomplexa Parasites (The Apicoplast) and Its Integrated Metabolism

International audienceChloroplasts are essential organelles that are responsible for photosynthesis in a wide range of organisms that have colonized all biotopes on Earth such as plants and unicellular algae. Interestingly, a secondary endosymbiotic event of a red algal ancestor gave rise to a group of organisms that have adopted an obligate parasitic lifestyle named Apicomplexa parasites. Apicomplexa parasites are some of the most widespread and poorly controlled pathogens in the world. These infectious agents are responsible for major human diseases such as toxoplasmosis, caused by Toxoplasma gondii, and malaria caused by Plasmodium spp. Most of these parasites harbor this relict plastid named the apicoplast, which is essential for parasite survival. The apicoplast has lost photosynthetic capacities but are metabolically similar to plant and algal chloroplasts. The apicoplast is considered a novel and important drug target against Apicomplexa parasites. This chapter focuses on the apicoplast of apicomplexa parasites, its maintenance, and its metabolic pathways