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AbstractClimate change is causing an increase in the frequency and intensity of marine heatwaves (MHWs) and mass mortality events (MMEs) of marine organisms are one of their main ecological impacts. Here, we show that during the 2015–2019 period, the Mediterranean Sea has experienced exceptional thermal conditions resulting in the onset of five consecutive years of widespread MMEs across the basin. These MMEs affected thousands of kilometers of coastline from the surface to 45 m, across a range of marine habitats and taxa (50 taxa across 8 phyla). Significant relationships were found between the incidence of MMEs and the heat exposure associated with MHWs observed both at the surface and across depths. Our findings reveal that the Mediterranean Sea is experiencing an acceleration of the ecological impacts of MHWs which poses an unprecedented threat to its ecosystems' health and functioning. Overall, we show that increasing the resolution of empirical observation is critical to enhancing our ability to more effectively understand and manage the consequences of climate change.

Global environmental change is affecting species distribution and their interactions with other species. In particular, the main drivers of environmental change strongly affect the strength of interspecific interactions with considerable consequences to biodiversity. However, extrapolating the effects observed on pair-wise interactions to entire ecological networks is challenging. Here we propose a framework to estimate the tolerance to changes in the strength of mutualistic interaction that species in mutualistic networks can sustain before becoming extinct. We identify the scenarios where generalist species can be the least tolerant. We show that the least tolerant species across different scenarios do not appear to have uniquely common characteristics. Species tolerance is extremely sensitive to the direction of change in the strength of mutualistic interaction, as well as to the observed mutualistic trade-offs between the number of partners and the strength of the interactions. Nature Communications 4, Article number: 2350, (2013)

27 pages, 11 figures, 2 tables.-- PMID: 9481143 [PubMed]. The major light-absorbing pigments in purple photosynthetic bacteria are the bacteriochlorophylls (a and b) (BChl) and the carotenoids. These pigments are noncovalently attached to two types of integral membrane protein forming the reaction centers and the light-harvesting or antenna complexes (Hawthornthwaite and Cogdell, 1991; Hunter, 1995; Zuber and Cogdell, 1995). Photosynthesis in purple bacteria usually begins with the absorption of a photon in the light-harvesting system. The absorbed energy is then rapidly (in less than ~100 ps) and efficiently transferred to the reaction center (~95% quantum efficiency). In the reaction center this energy is used to drive the initial charge separation reaction and the energy is then "trapped" (Feher and Okamura, 1978; Feher et al., 1989; Deisenhofer et al., 1995). The combination of antenna complexes with a reaction center constitutes the photosynthetic unit (PSU). For most commonly studied purple bacteria the number of PSUs per cell and their size are variable. Depending on such factors as the light-intensity at which cells are grown, the size of the PSU can vary from about 30 BChls per reaction center up to 200-300 BChls per reaction center (Aagaard and Sistrom, 1972; Drews, 1985). This arrangement of reaction centers surrounded by an antenna system ensures that each reaction center is kept well supplied with incoming solar energy and effectively acts to increase their cross-sectional area for photon capture. It is interesting to note that in most species the same pigments are found in both reaction centers and antenna complexes, and it is the protein that determines which function a given pigment is destined to fulfil. When BChl a is dissolved in an organic solvent such as 7:2 v/v acetone:methanol its NIR absorption band is located at 772 nm. This is the typical Qy absorption band of monomeric BChl a. However, when the BChl a is non-covalently bound into an antenna complex, this NIR absorption band is red shifted between 800-940 nm, depending on the species (Fig. 1) (Thornber et al., 1978; Hawthornthwaite and Cogdell, 1991). In most species this red shift is associated with an increase in spectral complexity, with several peaks/shoulders clearly visible in the in vivo absorption spectrum. This red shift arises from pigment-pigment and pigment-protein interactions within the antenna complexes and is regularly used to both identify them and judge their integrity. Since they are integral membrane proteins, the isolation of a purple bacterial antenna complex begins with the solubilization of the photosynthetic membrane with a suitable detergent (Cogdell and Thorber, 1979; Hawthornthwaite and Cogdell, 1991). Very often the solubilized complexes are then initially fractionated by sucrose gradient centrifugation (Fig. 2). In most species this fractionation reveals two types of antenna complex, called LH1 and LH2. LH1 forms the so called "core" complex. It is closely associated with the reaction center and forms a stoichiometric complex with it (usually ~32 BChls per reaction center (Gall, 1995; Karrasch et al., 1995; Zuber and Cogdell, 1995). LH2, also sometimes called the "variable" or "peripheral" antenna complex, is the topic for the remainder of this review. Readers who want to obtain more information on the overall subject of the structure and function of the bacterial PSU should consult the following general reviews (Somsen et al., 1993; Blankenship et al., 1995; Loach and Parkes-Loach, 1995; Cogdell et al., 1996; Papiz et al., 1996). Some of the work described in this review was supported by grants from the BBSRC, the EU and the Human Frontiers of Science Programme. RJC would like to thank the Alexander von Humboldt Foundation for financial support during the writing of this review. Peer reviewed

Significance Bacteria control biogeochemical cycles of elements and fluxes of energy in the ocean. Discovery of a membrane photoprotein widespread in marine bacteria—proteorhodopsin—expanded their potential importance for global energy budgets, providing a novel mechanism to harness light energy. Yet, how proteorhodopsin-derived energy is used for cell metabolism remains largely unexplored. We combined experiments in a model marine bacterium with gene expression analyses. Light-stimulated growth coincided with a shift in carbon acquisition pathways, with anaplerotic CO 2 fixation providing up to one-third of the cell carbon. Exposure to light resulted in the up-regulation of several central metabolism genes, including the glyoxylate shunt. Thus, light provides proteorhodopsin-containing bacteria with wider means to adapt to environmental variability than previously recognized.

Montane cloud forests are areas of high endemism, and are one of the more vulnerable terrestrial ecosystems to climate change. Thus, understanding how they both contribute to the generation of biodiversity, and will respond to ongoing climate change, are important and related challenges. The widely accepted model for montane cloud forest dynamics involves upslope forcing of their range limits with global climate warming. However, limited climate data provides some support for an alternative model, where range limits are forced downslope with climate warming. Testing between these two models is challenging, due to the inherent limitations of climate and pollen records. We overcome this with an alternative source of historical information, testing between competing model predictions using genomic data and demographic analyses for a species of beetle tightly associated to an oceanic island cloud forest. Results unequivocally support the alternative model: populations that were isolated at higher elevation peaks during the Last Glacial Maximum are now in contact and hybridizing at lower elevations. Our results suggest that genomic data are a rich source of information to further understand how montane cloud forest biodiversity originates, and how it is likely to be impacted by ongoing climate change.

Global environmental changes may have a profound impact on ecosystems. In this context, it is crucial to gather biological and ecological information of the main species in marine communities to predict and mitigate potential effects of shifts in their distribution, abundance, and interactions. Using genotyping by sequencing (GBS), we assessed the genetic structure of a keystone species in the Mediterranean shallow littoral ecosystems, the black sea urchin Arbacia lixula. This bioengineer species can shape their communities due to its grazing activity and it is experiencing an ongoing expansion with increasing temperatures. The population genomic analyses on 5,241 loci sequenced in 240 individuals from 11 Mediterranean sampled populations revealed that all populations were diverse and showed significant departure from equilibrium. Albeit genetic differentiation was in general shallow, a significant break separated the western and eastern Mediterranean populations, a break not detected in previous studies with less resolutive markers. Notably, no clear effect of the Almería-Oran front, an important break in the Atlanto-Mediterranean transition, could be detected among the western basin populations, where only a slight differentiation of the two northernmost populations was found. Despite the generally low levels of genetic differentiation found, we identified candidate regions for local adaptation by combining different genomic analysis with environmental data. Salinity, rather than temperature, seemed to be an important driver of genetic structure in A. lixula. Overall, from a population genomics standpoint, there is ample scope for A. lixula to continue thriving and adapting in the warming Mediterranean.