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.


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  • Seasonal bone growth and physiology in endotherms shed light on dinosaur physiology (2012)

    Köhler, Meike (ICP)

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    Seasonal bone growth and physiology in endotherms shed light on dinosaur physiology

    Cyclical growth leaves marks in bone tissue that are in the forefront of discussions about physiologies of extinct vertebrates. Ectotherms show pronounced annual cycles of growth arrest that correlate with a decrease in body temperature and metabolic rate; endotherms are assumed to grow continuously until they attain maturity because of their constant high body temperature and sustained metabolic rate. This apparent dichotomy has driven the argument that zonal bone denotes ectotherm-like physiologies, thus fuelling the controversy on dinosaur thermophysiology and the evolution of endothermy in birds and mammal-like reptiles.

    Our comprehensive global study of wild ruminants from tropical to polar environments shows that cyclical growth is a universal trait of homoeothermic endotherms. Growth is arrested during the unfavourable season concurrently with decreases in body temperature, metabolic rate and bone-growth-mediating plasma insulin-like growth factor-1 levels, forming part of a plesiomorphic thermometabolic strategy for energy conservation. Conversely, bouts of intense tissue growth coincide with peak metabolic rates and correlated hormonal changes at the beginning of the favourable season, indicating an increased efficiency in acquiring and using seasonal resources. Our study supplies the strongest evidence so far that homeothermic endotherms arrest growth seasonally, which precludes the use of lines of arrested growth as an argument in support of ectothermy. However, high growth rates are a distinctive trait of mammals, suggesting the capacity for endogenous heat generation. The ruminant annual cycle provides an extant model on which to base inferences regarding the thermophysiology of dinosaurs and other extinct taxa.

  • Interactions between amino acid sites guide protein evolution (2012)

    Kondrashov, Fyodor (CRG)

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    Interactions between amino acid sites guide protein evolution

    Amino acid sequences of proteins encoded in genomes of all walks of life change overtime. The study the changes, substitutions, of amino acids is one of the important pieces of the puzzle in trying to understand how genetic information predetermines species to show the features that they do. The prevailing debate in the field has focused on the issue of the mechanism that leads an emerging mutation to become common in the population and alters to fix, to completely replace the state that was present before the mutation arose. This question is formulated around the short-term timescales of evolution, focusing on individual mutations in isolation from each other and from other substitutions that may have occurred a long time before.

    Our study in collaboration with another group at the CRG focused on the effect of recent substitutions in relation to other substitutions that happened a long time ago. We asked the question of whether or not amino acid states that are observed in across the animal phylogeny are accepted with equal ease in all species; we studied whether or not an amino acid state that is observed in one animal would be inhibited from occurring in a different species. To this end we constructed large multiple alignments and measured the distribution of different amino acids across the sites in the protein. We then contrasted the short-term rates of substitution observed between closely related animals with the overall amino acid diversity across the animal clade. We observed that the overall amino acid diversity across long-term evolution is much larger than predicted by the short-term rates of evolution. Short-term substitutions are inhibited from occurring in one species, even if this substitution is creating an amino acid state that is present in some other species.

    Thus, if an amino acid state is present in one species in many cases it will be deleterious if placed into another species. How is this possible? The most straightforward explanation is that the impact of an amino acid is not independent of all other substitutions that make one species different from another. The impact of an amino acid substitution is not universal and in many cases must depend on the right combination with other substitutions to contribute positively to the phenotype of the organism. The map that relates sequence and fitness, the fitness landscape, is, therefore, highly rugged, with instances when the impact of a specific substitution may be highly deleterious in one combination but beneficial in another (Figure 1)

  • Mutations in cancer genomes (2012)

    Lehner, Ben (CRG)

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    Mutations in cancer genomes

    Cancer is primarily caused by somatic mutations - mutations that occur during our lifetime, not those that we inherit from our parents. But are all of our genes equally likely to mutate? Cancer genome sequencing projects allow this question to be properly addressed for the first time. Using publicly available data from different cancer genome sequencing projects shows that the rate at which genes mutate varies quite extensively in different regions of the human genome. Strikingly this regional variation in mutation rates seems to be quite consistent in different cell types (lung, breast, etc.) and for different types of mutations. What causes this regional variation? One important aspect seems to be how the genome is packaged. This may affect various cellular processes and can explain more than half of region-to-region variation. This suggests that the arrangement of the genome into 'closed' (heterochromatin) and 'open' (euchromatin) domains is a dominant influence on regional mutation-rate variation in human cells.

  • Publication book "Ultracold Atoms in Optical Lattices: Simulating Quantum Many-Body Systems" (2012)

    Lewenstein, Maciej Andrzej (ICFO)
    Sanpera Trigueros, Anna (UAB)

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    Publication book "Ultracold Atoms in Optical Lattices: Simulating Quantum Many-Body Systems"

    The book "Ultracold Atoms in Optical Lattices: Simulating Quantum Many-Body Systems" (Oxford University Press, Oxford, 2012), written by ICREA Research Professors Maciej Lewenstein and Anna Sanpera, and former ICREA researcher Veronica Ahufinger, is the first book ever that treats extensively (460 pages and several thousands references) the rapidly developing subject of quantum computers of special purpose, a.k.a. quantum simulators. Quantum simulators are currently being realized in various experiments, in particular in experiments with ultracold atoms or molecules in optical lattices, or ultracold trapped ions. It is expected that in the next future quantum simulators will help us to understand better quantum many-body phenomena, from high temperature superconductivity to quark confinement. The book focuses on atoms and molecules in optical lattices and, besides providing a general introduction to the subject, it discusses in great detail ultracold atomic/molecular systems that can simulate spin models, dipolar systems, disordered systems, frustrated systems and systems under influence of intense gauge fields. The book focuses on atoms and molecules in optical lattices and, apart of providing general introduction to the subject, discusses in great detail ultracold atomic/molecular systems that can simulate spin models, dipolar systems, disordered systems, frustrated systems and systems under influence of intense gauge fields.

  • The Discovery of a Higgs-Like Boson at the LHC (2012)

    Martínez Pérez, Mario (IFAE)

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    The Discovery of a Higgs-Like Boson at the LHC

    Since 2009, the Large Hadron Collider (LHC) at CERN (Geneva, Switzerland) collides protons at center-of-mass energies of up to 8 TeV, the highest energy ever reached by a particle accelerator. One of the main goals of the LHC is the search for the Higgs boson, the last missing piece of the Standard Model (SM). The Higgs boson is the particle associated with a quantum field postulated to permeate the Universe and responsible for endowing elementary particles with their mass. Unfortunately, the mass of the Higgs boson is not predicted, making its search particularly challenging.
    During the last 48 years, particle physicists have searched for the Higgs boson. In the 90's, the LEP electron-positron collider at CERN concluded that the Higgs boson, if it exists, should have a mass larger than 114.4 GeV at 95% confidence level (C.L). The search continued at the 1.96 TeV proton-antiproton Tevatron collider at Fermilab (Chicago, USA), till the accelerator was shut down on September 2011. While the Tevatron experiments achieved sensitivity to a SM Higgs boson up to a mass of 185 GeV, no definite signal was established.
    On July 4, 2012, under lots of excitement and extensive media coverage, the ATLAS and CMS experiments reported at a public seminar at CERN the results of their searches for the SM Higgs boson using the data collected during 2010-2012. In particular, the combination of searches at the ATLAS experiment excluded at 95% C.L. the presence of a Higgs boson with mass between 111 GeV and 559 GeV, with the exception of the range 122-131 GeV [1]. In this mass range a signal-like excess was observed at a mass of ~126 GeV, primarily in the searches targeting the decay modes into two photons (see Fig. 1) and into four charged leptons (see Fig. 2). The significance of the excess was estimated at 5.9 standard deviations from the background-only hypothesis, with a similar signal also observed by the CMS experiment [2]. This represents the discovery of a new boson with properties compatible with those of the SM Higgs boson, marking the beginning of a new era in particle physics. The ATLAS discovery has been recently discussed in a special edition of the Science journal [3].
    In order to unravel the nature of this particle, precise measurements of its properties are of crucial importance. A. Juste and M. Martínez lead the analysis effort of the ATLAS data at IFAE, playing a central role in those channels where the Higgs boson is produced in association with a pair of top quarks or a Z boson in the final state, and decay

  • Global convergence in the vulnerability of forests to drought (2012)

    Mencuccini, Maurizio (CREAF)

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    Global convergence in the vulnerability of forests to drought

    Shifts in rainfall patterns and increasing temperatures associated with climate change are likely to cause widespread forest decline in regions where droughts are predicted to increase in duration and severity. One primary cause of productivity loss and plant mortality during drought is hydraulic failure. Drought stress creates trapped gas emboli in the water transport system, which reduces the ability of plants to supply water to leaves for photosynthetic gas exchange and can ultimately result in desiccation and mortality. At present we lack a clear picture of how thresholds to hydraulic failure vary across a broad range of species and environments, despite many individual experiments. Here we draw together published and unpublished data on the vulnerability of the transport system to drought-induced embolism for a large number of woody species, with a view to examining the likely consequences of climate change for forest biomes. We show that 70% of 226 forest species from 81 sites worldwide operate with narrow hydraulic safety margins against injurious levels of drought stress and therefore potentially face long-term reductions in productivity and survival if temperature and aridity increase as predicted for many regions across the globe. Safety margins are largely independent of mean annual precipitation, showing that there is global convergence in the vulnerability of forests to drought, with all forest biomes equally vulnerable to hydraulic failure regardless of their current rainfall environment. These findings provide insight into why drought-induced forest decline is occurring not only in arid regions but also in wet forests not normally considered at drought risk.