25 research outputs found
Is oxygen limitation in warming waters a valid mechanism to explain decreased body sizes in aquatic ectotherms?
Aim:The negative correlation between temperature and body size of ectothermic animals (broadly known as the temperatureâsize rule or TSR) is a widely observed pattern, especially in aquatic organisms. Studies have claimed that the TSR arises due to decreased oxygen solubility and increasing metabolic costs at warmer temperatures, whereby oxygen supply to a large body becomes increasingly difficult. However, mixed empirical evidence has led to a controversy about the mechanisms affecting speciesâ size and performance under different temperatures. We review the main competing genetic, physiological and ecological explanations for the TSR and suggest a roadmap to move the field forward.
Location: Global.
Taxa: Aquatic ectotherms.
Time period: 1980âpresent.
Results: We show that current studies cannot discriminate among alternative hypotheses and none of the hypotheses can explain all TSRârelated observations. To resolve this impasse, we need experiments and fieldâsampling programmes that specifically compare alternative mechanisms and formally consider energetics related to growth costs, oxygen supply and behaviour. We highlight the distinction between evolutionary and plastic mechanisms, and suggest that the oxygen limitation debate should separate processes operating on short, decadal and millennial timeâscales.
Conclusions: Despite decades of research, we remain uncertain whether the TSR is an adaptive response to temperatureârelated physiological (enzyme activity) or ecological changes (food, predation and other mortality), or a response to constraints operating at a cellular level (oxygen supply and associated costs). To make progress, ecologists, physiologists, modellers and geneticists should work together to develop a crossâdisciplinary research programme that integrates theory and data, explores timeâscales over which the TSR operates, and assesses limits to adaptation or plasticity. We identify four questions for such a programme. Answering these questions is crucial given the widespread impacts of climate change and reliance of management on models that are highly dependent on accurate representation of ecological and physiological responses to temperature
Marine fish traits follow fast-slow continuum across oceans
A fundamental challenge in ecology is to understand why species are found where they are and predict
where they are likely to occur in the future. Trait-based approaches may provide such understanding,
because it is the traits and adaptations of species that determine which environments they can inhabit.
It is therefore important to identify key traits that determine species distributions and investigate
how these traits relate to the environment. Based on scientific bottom-trawl surveys of marine fish
abundances and traits of >1,200 species, we investigate trait-environment relationships and project
the trait composition of marine fish communities across the continental shelf seas of the Northern
hemisphere. We show that traits related to growth, maturation and lifespan respond most strongly to
the environment. This is reflected by a pronounced âfast-slow continuumâ of fish life-histories, revealing
that traits vary with temperature at large spatial scales, but also with depth and seasonality at more
local scales. Our findings provide insight into the structure of marine fish communities and suggest that
global warming will favour an expansion of fast-living species. Knowledge of the global and local drivers
of trait distributions can thus be used to predict future responses of fish communities to environmental
change.Postprint2,92
Ontogenetic deepening of Northeast Atlantic fish stocks is not driven by fishing exploitation
For many marine fish species, the average size of individuals increases with depth. This phenomenon, first described a century ago, is known as ontogenetic deepening (1, 2). Several mechanisms have been proposed to explain it: optimal foraging; predation avoidance; and different optimal growth temperature for larger individuals, causing them to seek deeper and cooler waters to optimize growth and reproduction (3). In their recent paper in PNAS, Frank et al. (4) suggest an alternative explanation. They examined age-structured data from Atlantic cod (Gadus morhua) on the eastern Scotian Shelf, a stock that has experienced successive periods of intense, and absence of, fishing. In their study, fishing explained 72% of the variation in the observed age-related deepening, with the remaining variability attributed to ontogenetic deepening. They conclude that higher abundances of large fish in deeper waters is an artifact of greater fishing intensity at shallower depths and question whether ontogenetic deepening is a real ecological phenomenon
Role of neuroinflammation in neurodegeneration: new insights
Previously, the contribution of peripheral infection to cognitive decline was largely overlooked however, the past 15Â years have established a key role for infectious pathogens in the progression of age-related neurodegeneration. It is now accepted that the immune privilege of the brain is not absolute, and that cells of the central nervous system are sensitive to both the inflammatory events occurring in the periphery and to the infiltration of peripheral immune cells. This is particularly relevant for the progression of Alzheimerâs disease, in which it has been demonstrated that patients are more vulnerable to infection-related cognitive changes. This can occur from typical infectious challenges such as respiratory tract infections, although a number of specific viral, bacterial, and fungal pathogens have also been associated with the development of the disease. To date, it is not clear whether these microorganisms are directly related to Alzheimerâs disease progression or if they are opportune pathogens that easily colonize those with dementia and exacerbate the ongoing inflammation observed in these individuals. This review will discuss the impact of each of these challenges, and examine the changes known to occur with age in the peripheral immune system, which may contribute to the age-related vulnerability to infection-induced cognitive decline