Highlights

Every year, a committee of experts sits down with a tough job to do: from among all ICREA publications, they must find a handful that stand out from all the others. This is indeed a challenge. The debates are sometimes heated and always difficult but, in the end, a shortlist of  the most outstanding publications of the year is produced. No prize is awarded, and the only additional acknowledge is the honour of being chosen and highlighted by ICREA. Each piece has something unique about it, whether it be a particularly elegant solution, the huge impact it has in the media or the sheer fascination it generates as a truly new idea. For whatever the reason, these are the best of the best and, as such, we are proud to share them here.

LIST OF SCIENTIFIC HIGHLIGHTS

Format: yyyy

  • Dwarfing in Hipparions - selection for size o selection for age at maturity? (2018)

    Köhler, Meike (ICP)

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    Dwarfing in Hipparions - selection for size o selection for age at maturity?

    Hipparions, the classical three-toed horses, repeatedly evolved dwarf forms, some of them as small as medium-sized dogs. Such size shifts are not unusual amongst insular mammals (fossil and extant), but they are less frequent in continental settings. Dwarfism on islands is commonly considered as a result of low resource availability directly limiting body size; however a more recent model by Palkovacs (2003) proposes that selection instead may act on key life cycle traits such as age at maturity or the age at first reproduction, and that shifts in body size are a simple byproduct. This approach has predictive power and enjoys empirical support. It allows a better understanding of the environmental conditions as it predicts the magnitude of selection pressure exerted by either predation or resource availability. 

    We adopted this approach to predict the paleoenvironment of continental dwarf hipparions from Eastern and Western Mediterranian bioprovinces, where the ecological conditions are still heavily debated. We reconstructed growth rates from bone histology for different-sized hipparionins from Greece and Spain, and found that dwarfing was triggered by different mechanisms in these regions. While Greek hipparions  ceased growth early at a small size, thus advancing maturity, Spanish hipparions grew at slower rates and matured later, however at a similar small size. Based on Palkovacs' model, we infer that the Greek dwarfs suffered high adult mortality by predation, while the Spanish dwarfs faced low resource supply associated with high juvenile mortality.

    We conclude that different selective pressures - high predation pressure, low resource availability - trigger different changes in key life history traits (age at maturity) that result in similar shifts towards smaller size. Thus, there is no direct relation between observed body size and environmental conditions as hitherto believed, which calls for analyses within the framework of life history theory to resolve the mechanisms underlying size changes. 

  • Mimicking solid state with ultracold atoms in optical lattices: Toy models of phonons (2018)

    Lewenstein, Maciej Andrzej (ICFO)

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    Mimicking solid state with ultracold atoms in optical lattices: Toy models of phonons

    Phonons, that is, excitations of modulations of the crystalline lattices being the basic structures of solid state, play fundamental role in condensed matter physics, leading to various phonon induced phenomena from semiconduction to Peierls instability, i.e., formation of antiferromagnetism, and topological order.  We have introduced a family of lattice models were phonon dynamics is reduced to that of two state models. This allows to simulate such systems efficiently in one or two dimensions and study their peculiar properties, such as spontaneous formation of stable antiferromagnetism, formation of topological order, etc.

  • The mysterious periodicity of the genome (2018)

    López-Bigas, Núria (IRB Barcelona)

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    The mysterious periodicity of the genome

    Meters of DNA are highly compacted into each cell’s nucleus. The most basic structure of this compaction are nucleosomes. 147 bps of DNA wrapped around proteins called histones. Every 10bps, the minor groove of the DNA faces towards or away from histones.

    Through the study of the distribution of somatic mutations in more than 3,000 human tumours, we have discovered that this 10bp periodic structure of the DNA around nucleosomes produces a periodicity in the rate of generation of somatic mutations. The periodic pattern was also observed in germline mutations, which are passed on to the offspring.

    Along the genomes of eukaryotes, A/T di-nucleotides are more likely to occur with a10bp- periodicity (WW periodicity) , which has long been associated to the presence of nucleosomes. This WW periodicity has been speculated to have arisen through selection of mutations conducive to sequences that favor the bending of DNA around nucleosomes. We propose that the periodic rate of somatic and germline mutations that we observed could have contributed through evolutionary time to the generation of the WW periodic pattern in the genomes of eukaryotes (Figure).

    The findings presented here have strong implications for understanding mutational and repair processes in human DNA, understanding the evolution of eukaryotic genomes, and for the study somatic and germline evolutionary processes.

  • Experiments and modelling in quest for high fusion performance (2018)

    Mantsinen, Mervi Johanna (BSC-CNS)

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    Experiments and modelling in quest for high fusion performance

    Our recent research results have advanced the understanding of how to reach high fusion performance in fusion experiments in the Joint European Torus (JET), in preparation of ITER. JET is the largest experimental fusion device in operation today and the only one capable of using the fusion reactor relevant fuel mixture of heavy hydrogen isotopes deuterium (D) and tritium (T).

    Our research has focused on the impact of neutral beam injection (NBI) and ion cyclotron resonance frequency (ICRF) heating on the fusion yield. These heating methods will be used in ITER to heat the fuel to high temperatures required for fusion. The main ICRF scheme that we have studied both experimentally and computationally at JET is heating of minority hydrogen ions in a D plasma with D beam ions. Apart from the D plasma scenario, we have also investigated the deuterium-tritium (DT) plasma scenario through an extrapolation of D high-performance discharges.

    Our experimental and modelling results have allowed us to draw several important conclusions regarding the role of auxiliary heating on the fusion plasma performance, which helps us to improve the fusion plasma performance in the forthcoming campaign with D-T fuel mixture at JET. One of the main goals for this flagship campaign is to achieve world-record fusion performance for a duration of more than 5 s.

  • Holography, Hydrodynamics and the Quark-Gluon Plasma (2018)

    Mateos, David (UB)

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    Holography, Hydrodynamics and the Quark-Gluon Plasma

    At low energies quarks and gluons are confined inside the protons and neutrons contained in the atoms that we and the things around us are made of. However, at a temperature of one trillion degrees (a hundred thousand times the temperature at the centre of the Sun) thermal fluctuations are so violent that quarks and gluons become liberated and give rise to a new form of matter known as "Quark-Gluon Plasma" (QGP). The QGP filled the Universe about one microsecond after the Big Bang and it has been be recreated on Earth in so-called Heavy Ion Collision experiments (HIC). 

    One of the main discoveries of these experiments is that the QGP behaves as an almost-perfect fluid that is well described by hydrodynamics. This is crucial because hydrodynamics is the bridge that allows us to connect theory with experiment. We have investigated the applicability of hydrodynamics in the regime that will be explored by HIC experiments over the next decade. Since this is difficult with conventional methods, we have used a string-theoretical tool known as "holography", which maps the properties of matter in our four-dimensional world to those of … gravity in five dimensions! 

    We have discovered that the formulation of hydrodynamics that is almost universally used in hydrodynamic codes, the so-called Muller-Israel-Stewart (MIS) formulation, may not capture correctly the physics of the QGP in the new regime, which could potentially jeopardize our interpretation of the next generation of experiments. 

    Fortunately, by formulating the problem in terms of five-dimensional gravity, holography also suggests a solution that is currently under investigation.

  • Global trait–environment relationships of plant communities (2018)

    Mencuccini, Maurizio (CREAF)

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    Global trait–environment relationships of plant communities

    Terrestrial ecosystems (e.g., grasslands, forests) provide a variety of services to human societies, for example climate regulation, provision of water, energy and materials such as timber or animal fodder. These ecosystem ‘functions’ depend on the species (grasses, shrubs, trees) that make up these ecosystems. It is now known that it is not so much the taxonomy of the species that matter, but rather how their leaves, stems and roots are made, i.e., their ‘functional’ attributes, or traits. When a grassland or a forest community is composed of many species, it is the community-level average of the traits of all the component species that defines the level of the observed ecosystem function. Key questions are a) to what extent these community-level trait compositions differ globally, and b) whether environmental drivers at local and/or global scale affect community-level trait values. Here, we perform a global, plot-level analysis of trait–environment relationships, using a database with more than 1.1 million vegetation plots and 26,632 plant species with trait information. We find two main community-level trait axes that capture half of the global trait variation across these 1.1 million vegetation plots. These two axes represent plant stature and leaf traits controlling resource acquisitiveness (light, nutrients, etc), similar to prior results at the scale of individual species. We found that climate and soil conditions at the global scale exert only a weak control on community-level trait averages. Our results indicate that, at a fine spatial grain, macro-environmental drivers are much less important for functional trait composition than has been previously assumed. Instead, trait combinations seem to be predominantly filtered by local-scale factors such as disturbance, fine-scale soil conditions, niche partitioning and biotic interactions.

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