Humans are rapidly transforming the structural configuration of the planet's ecosystems, but these changes and their ecological consequences remain poorly quantified in underwater habitats. Here, we ...show that the loss of forest‐forming seaweeds and the rise of ground‐covering ‘turfs’ across four continents consistently resulted in the miniaturization of underwater habitat structure, with seascapes converging towards flattened habitats with smaller habitable spaces. Globally, turf seascapes occupied a smaller architectural trait space and were structurally more similar across regions than marine forests, evidencing habitat homogenization. Surprisingly, such habitat convergence occurred despite turf seascapes consisting of vastly different species richness and with different taxa providing habitat architecture, as well as across disparate drivers of marine forest decline. Turf seascapes contained high sediment loads, with the miniaturization of habitat across 100s of km in mid‐Western Australia resulting in reefs retaining an additional ~242 million tons of sediment (four orders of magnitude more than the sediments delivered fluvially annually). Together, this work demonstrates that the replacement of marine forests by turfs is a generalizable phenomenon that has profound consequences for the ecology of temperate reefs.
We show that the loss of forest‐forming seaweeds and the rise of ground‐covering ‘turfs’ across four continents consistently resulted in the homogenization and miniaturization of underwater habitat structure across regions. We estimate that this miniaturization led some reefs to retain several hundred million tons of additional sediment. This work demonstrates that the replacement of marine forests by turfs is a generalizable phenomenon that has profound consequences for the ecology of temperate reefs.
Predicting where state-changing thresholds lie can be inherently complex in ecosystems characterized by nonlinear dynamics. Unpacking the mechanisms underlying these transitions can help considerably ...reduce this unpredictability. We used empirical observations, field and laboratory experiments, and mathematical models to examine how differences in nutrient regimes mediate the capacity of macrophyte communities to sustain sea urchin grazing. In relatively nutrient-rich conditions, macrophyte systems were more resilient to grazing, shifting to barrens beyond 1 800 g m−2 (urchin biomass), more than twice the threshold of nutrient-poor conditions. The mechanisms driving these differences are linked to how nutrients mediate urchin foraging and algal growth: controlled experiments showed that low-nutrient regimes trigger compensatory feeding and reduce plant growth, mechanisms supported by our consumer–resource model. These mechanisms act together to halve macrophyte community resilience. Our study demonstrates that by mediating the underlying drivers, inherent conditions can strongly influence the buffer capacity of nonlinear systems.
Plant–herbivore interactions are often regulated by a series of direct and indirect buffer mechanisms (compensatory or defensive plant responses, population control, alternative resources) that can ...determine the relative stability of the system. In plant‐dominated marine environments, these mechanisms are particularly important given how vulnerable these systems are to strong consumer pressure. Here, we evaluate the presence and, where possible, the strength, of five mechanisms that get activated under high herbivory pressure and are capable of dampening their effects in a seagrass meadow ecosystem: 1) seagrass compensatory growth, 2) increase in plant resistance, 3) availability of alternative resources, 4) predatory control and 5) density‐dependent control. We assessed these mechanisms for the interaction between the Mediterranean seagrass Posidonia oceanica and the sea urchin Paracentrotus lividus through a short‐term series of controlled field and laboratory experiments after simulated or natural herbivory events. Of the five mechanisms tested, we found that three mechanisms – availability of alternative resources, increased predation rate and reduction in sea urchin numbers – effectively dampened herbivory and worked as potential buffering mechanisms. In contrast, plant compensatory growth and resistance did not show clear responses. While compensatory growth and plant resistance are direct plant mechanism to tolerate the effects of herbivory, the rest are indirect mechanisms that begin with a modification of a plant trait (i.e. canopy height) that influences other species preference and/or behaviour, which in turn influences plant consumption. These adaptive behaviours may be a crucial and often overlooked factor in the remarkable resilience that Mediterranean seagrass ecosystems show to herbivory.
Herbivore outbreaks often trigger catastrophic overgrazing events in marine macrophyte ecosystems. The sea urchin Paracentrotus lividus, the dominant herbivore of shallow Mediterranean seascapes, is ...capable of precipitating shifts to barrens when its populations explode. Paracentrotus lividus is found ubiquitously in rocky macroalgal communities and in sandy seagrass meadows of Posidonia oceanica, two of the most important subtidal habitats in the Mediterranean. We explored if habitat‐specific regulation across the principal stages of the urchin life cycle could help explain the persistence of these populations in connected mosaics. We measured each of three relevant ecological processes (i.e. settlement, post‐settlement survival and predation) across a wide stretch of the Mediterranean coast (ca 600 km). Our results show that habitat‐specific regulation is critical in determining urchin populations: each habitat limited urchin sub‐populations at different life stages. Settlement was never limiting; urchins settled at similar rates in both habitats across the coast. Post‐settlement survival was a clear bottleneck, particularly in seagrass meadows where no juvenile urchins were recorded. Despite this bottleneck in seagrasses, adult urchin populations were very similar in both seagrass and macroalgal habitats indicating that other processes (potentially migration) could be key in determining adult distributions across the mosaic. The fact that population regulation is clearly habitat‐specific suggests that sea urchin populations may be significantly buffered from bottlenecks in mixed seascapes where both habitats co‐occur. Sea urchin populations can therefore persist across the seascape despite strong habitat‐specific regulation either by maintaining reproductive output in one habitat or by migrating between them. By affording these regulatory escapes to habitat‐modifying species, patchy mosaics may be much more prone to herbivore outbreaks and a host of cascading effects that come in their wake.
Oxidative stress has been implicated in the pathogenesis of several neurodegenerative diseases including Alzheimer's disease (AD). Several proteins have been identified as targets of oxidative damage ...in AD dementia (usually stages V/VI of Braak) and in subjects with mild cognitive impairment associated with middle stages of AD pathology (stage IV of Braak). In this study, we investigate whether brain proteins are locally modified by oxidative stress at the first stages of AD‐related pathology when morphological lesions are restricted to the entorhinal and transentorhinal cortices of neurofibrillary pathology (stages I/II of Braak). Using a proteomic approach, we show that the α subunit of the mitochondrial adenosine triphosphate (ATP)‐synthase is distinctly lipoxidized in the entorhinal cortex at Braak stages I/II compared with age‐matched controls. In addition, ATP‐synthase activity is significantly lower in Braak stages I/II than age‐matched control, while electron transport chain, expressed by the mitochondrial complex I activity, remains not affected. This is the first study showing oxidative damage in the first stage, and clinically silent period, of AD‐related pathology characterized by entorhinal and transentorhinal tauopathy.
Docosahexaenoic acid (DHA) is an essential fatty acid modulating key nervous system functions, including neuroinflammation, and regulation of pre- and postsynaptic membrane formation. DHA ...concentration decreases in the lumbar spinal cord (LSC) of amyotrophic lateral sclerosis (ALS) patients and murine preclinical models. Using a dietary supplementation, we increased DHA levels (2% mean increase,
p
< 0.01) in the LSC of the familial ALS murine model B6SJL-Tg(SOD1*G93A)1Gur/J. This DHA-enriched diet significantly increases male mouse survival by 7% (average 10 days over 130 days of life expectancy), and delays motor dysfunction (based on stride length) and transgene-associated weight loss (
p
< 0.01). DHA supplementation led to an increased anti-inflammatory fatty acid profile (
ca
30%,
p
< 0.01) and a lower concentration of circulating proinflammatory cytokine TNF-α (
p
< 0.001 in males). Furthermore, although DHA-treated mice did not exhibit generally decreased protein oxidative markers (glutamic and aminoadipic semialdehydes, carboxyethyllysine, carboxymethyllysine, and malondialdehydelysine), dietary intake of DHA reduced immunoreactivity towards DNA oxidative damage markers (8-oxo-dG) in the LSC.
In vitro
we demonstrate that DHA and α-tocopherol addition to a model of motor neuron demise (neonatal rat organotypic spinal cord model under chronic excitotoxicity) also preserves motor neuron number, in comparison with untreated spinal cords. Also, beneficial effects on cell viability were evidenced for the motor neuron cell line NSC-34 in front of H
2
O
2
insult (
p
< 0.001). Globally we show a sex-specific benefit of dietary DHA supplementation in the G93A ALS mouse model, compared with mice fed an isocaloric control or a n-3-depleted diet. These changes were associated with an increased DHA concentration in the LSC and were compatible with
in vitro
results showing DHA neuroprotective properties. These results suggest the need for further study on the interaction of gender-influenced biological parameters and DHA in ALS pathogenesis.
Light gradients are ubiquitous in marine systems as light reduces exponentially with depth. Seagrasses have a set of mechanisms that help them to cope with light stress gradients. Physiological ...photoacclimation and clonal integration help to maximize light capture and minimize carbon losses. These mechanisms can shape plants minimum light requirements (MLR), which establish critical thresholds for seagrass survival and help us predict ecosystem responses to the alarming reduction in light availability.
Using the seagrass
as a case study, we compare the MLR under different carbon model scenarios, which include photoacclimation and/or self-facilitation (based on clonal integration) and that where parameterized with values from field experiments.
Physiological photoacclimation conferred plants with increased tolerance to reducing light, approximately halving their MLR from 5-6% surface irradiance (SI) to ≈ 3% SI. In oligotrophic waters, this change in MLR could translate to an increase of several meters in their depth colonization limit. In addition, we show that reduced mortality rates derived from self-facilitation mechanisms (promoted by high biomass) induce bistability of seagrass meadows along the light stress gradient, leading to abrupt shifts and hysteretic behaviors at their deep limit.
The results from our models point to (i) the critical role of physiological photoacclimation in conferring greater resistance and ability to recover (i.e., resilience), to seagrasses facing light deprivation and (ii) the importance of self-facilitating reinforcing mechanisms in driving the resilience and recovery of seagrass systems exposed to severe light reduction events.
Metabolomic and lipidomic analyses have been used for the profiling of neurodegenerative processes, both in targeted and untargeted approaches. In this work we have applied these techniques to the ...study of CSF samples of multiple sclerosis (MS) patients (n = 9), compared with samples of non‐MS individuals (n = 9) using mass‐spectrometry. We have used western‐blot and analyzed cell culture to confirm pathogenic pathways suggested by mass‐spectrometric measurements. The results of the untargeted approach of metabolomics and lipidomics suggest the existence of several metabolites and lipids discriminating both populations. Applying targeted lipidomic analyses focused to a pathogenic pathway in MS, oxidative stress, reveal that the lipid peroxidation marker 8‐iso‐prostaglandin F2α is increased in CSF from MS patients. Furthermore, as lipid peroxidation exerts its pathogenical effects through protein modification, we studied the incidence of protein lipoxidation, revealing specific increases in carboxymethylated, neuroketal and malondialdehyde‐mediated protein modifications in proteins of CSF from MS patients, despite the absence of their precursors glyoxal and methylglyoxal. Finally, we report that the level of neuroketal‐modified proteins correlated with a hitherto unknown increased amount of autoantibodies against lipid peroxidation‐modified proteins in CSF, without compensation by signaling induced by lipid peroxidation via peroxisome proliferator‐activated receptor γ (PPARγ). The results, despite the limitation of being obtained in a small population, strongly suggest that autoimmunity against in situ produced epitopes derived from lipid peroxidation can be a relevant pathogenic factor in MS.
A wrong response against wrong lipids: lipid peroxidation autoantibodies in multiple sclerosis. This study was aimed at obtaining a metabolomic and lipidomic fingerprint of multiple sclerosis. The results reveal both increased and specific lipid peroxidation in this disease, which is associated to the presence of autoantibodies against proteins modified with lipid peroxidation. This data uncovers a potential novel, lipid‐peroxidation based, autoimmune response in multiple sclerosis pathophysiology
1 Grup de Metabolisme Energètic i Nutrició, Departament de Biologia Fonamental i Ciències de la Salut, Institut Universitari dInvestigació en Ciències de la Salut, Universitat de les Illes Balears, ...Palma de Mallorca; and 2 Unitat de Biofísica, Departament de Ciències Fisiològiques II, Universitat de Barcelona, Barcelona, Spain
Submitted 27 January 2005
; accepted in final form 25 March 2005
In the present study, we have investigated gender differences in rat liver mitochondrial oxidative metabolism. Total mitochondrial population (M) as well as the heavy (M1), medium (M3), and light (M8) mitochondrial fractions obtained by means of differential centrifugation steps at 1,000, 3,000, and 8,000 g , respectively, were isolated. Electron microscopic analysis was performed and mitochondrial protein content and cardiolipin levels, mitochondrial O 2 flux, ATP synthase activity, mitochondrial membrane potential, and mitochondrial transcription factor A (TFAM) protein levels were measured in each sample. Our results indicate that mitochondria from females have higher protein content and higher cardiolipin levels, greater respiratory and phosphorylative capacities, and more-energized mitochondria in respiratory state 3 . Moreover, protein levels of TFAM were four times greater in females than in males. Gender differences in the aforementioned parameters were more patent in the isolated heavy M1 and M3 mitochondrial fractions. The present study demonstrates that gender-related differences in liver mitochondrial function are due mainly to a higher capacity and efficiency of substrate oxidation, likely related to greater mitochondrial machinery in females than in males, which is in accord with greater mitochondrial differentiation in females.
energy metabolism; mitochondrial biogenesis; high-resolution respirometry; mitochondrial membrane potential; mitochondrial transcription factor A
Address for reprint requests and other correspondence: M. Gianotti, Departament de Biologia Fonamental i Ciències de la Salut, Universitat de les Illes Balears, Carretera de Valldemossa km 7.5, E-07122 Palma de Mallorca, Spain (e-mail: magdalena.gianotti{at}uib.es )
Multiple anthropogenic stressors are causing a global decline in foundation species, including macrophytes, often resulting in the expansion of functionally different, more stressor‐tolerant ...macrophytes. Previously subdominant species may experience further positive demographic feedback if they are exposed to weaker plant–herbivore interactions, possibly via decreased palatability or being structurally different from the species they are replacing. However, the consequences of the spread of opportunistic macrophytes for the local distribution and life history of herbivores are unknown.
The green alga, Caulerpa filiformis, previously a subdominant macrophyte on low intertidal‐shallow subtidal rock shores, is becoming locally more abundant and has spread into warmer waters across the coast of New South Wales, Australia.
In this study, we measured (a) the distribution and abundance of a key consumer, the sea urchin Heliocidaris erythrogramma, across a seascape at sites where C. filiformis has become dominant, (b) performed behavioral field experiments to test the role of habitat selection in determining the local distribution of H. erythrogramma, and (c) consumer experiments to test differential palatability between previously dominant higher quality species like Ecklonia radiata and Sargassum sp. and C. filiformis and the physiological consequences of consuming it.
At all sites, urchin densities were positively correlated with distance away from C. filiformis beds, and they actively moved away from beds. Feeding experiments showed that, while urchins consumed C. filiformis, sometimes in equal amounts to higher quality algae, there were strong sublethal consequences associated with C. filiformis consumption, mainly on reproductive potential (gonad size). Specifically, the gonad size of urchins that fed on C. filiformis was equivalent to that in starved urchins. There was also a tendency for urchin mortality to be greater when fed C. filiformis.
Overall, strong negative effects on herbivore life‐history traits and potentially their survivorship may establish further positive feedback on C. filiformis abundance that contributes to its spread and may mediate shifts from top‐down to bottom‐up control at locations where C. filiformis has become dominant.
The spread of the previously subdominant Caulerpa filiformis along the coast of NSW, Australia has strong lethal and sublethal effects on a key herbivore population. We performed sea urchin surveys, behavioral experiments, and consumer experiments and found that Caulerpa has strong negative effects on their populations. These results may establish reinforcing feedbacks on the spreading algae and mediate shifts from top‐down to bottom‐up control.
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