Oxygen- and capacity-limited thermal tolerance: bridging ecology and physiology

Abstract

Observations of climate impacts on ecosystems highlight the need for an understanding of organismal thermal ranges and their implications at the ecosystem level. Where changes in aquatic animal populations have been observed, the integrative concept of oxygen-and capacitylimited thermal tolerance (OCLTT) has successfully characterised the onset of thermal limits to performance and field abundance. The OCLTT concept addresses the molecular to whole-animal mechanisms that define thermal constraints on the capacity for oxygen supply to the organism in relation to oxygen demand. The resulting 'total excess aerobic power budget' supports an animal's performance (e.g. comprising motor activity, reproduction and growth) within an individual's thermal range. The aerobic power budget is often approximated through measurements of aerobic scope for activity (i.e. the maximum difference between resting and the highest exerciseinduced rate of oxygen consumption), whereas most animals in the field rely on lower (i.e. routine) modes of activity. At thermal limits, OCLTT also integrates protective mechanisms that extend time-limited tolerance to temperature extremes -mechanisms such as chaperones, anaerobic metabolism and antioxidative defence. Here, we briefly summarise the OCLTT concept and update it by addressing the role of routine metabolism. We highlight potential pitfalls in applying the concept and discuss the variables measured that led to the development of OCLTT. We propose that OCLTT explains why thermal vulnerability is highest at the whole-animal level and lowest at the molecular level. We also discuss how OCLTT captures the thermal constraints on the evolution of aquatic animal life and supports an understanding of the benefits of transitioning from water to land.

Nonspecific stress response to temperature increase in Gammarus lacustris Sars with respect to oxygen-limited thermal tolerance concept

“…It is notable that accumulation of the most toxic lipid peroxides (triene conjugates and Schiff bases) in phospholipids occurs at the same time and temperature of exposure as the accumulation of lactate (Vereshchagina et al, 2016). This supports the concept of oxygen-and capacity-limited thermal tolerance (OCLTT) (Pörtner, Bock & Mark, 2017). The concept deals with molecular mechanisms sustaining oxygen metabolism, which determine the thermal tolerance limits for each species.…”

Phenotypic Plasticity in Animals Exposed to Osmotic Stress – Is it Always Adaptive?

“…Besides those phenotypic adjustments concerning osmoregulation, processes involving other physiological parameters have been intensely studied, especially those dealing with thermal acclimation, metabolic responses to hypoxia or excercise‐dependent plasticity in skeletal muscle . While we begin to understand the evolutionary principles of creating molecular diversity as the genetic basis for acclimation, there are only some initial trials to understand the underlying molecular mechanisms (sensing, signaling, gene transcription, RNA processing, post‐translational modifications, etc.)…”

Embryonic canalization and its limits—A view from temperature

“…Temperature is clearly a major environmental parameter affecting development and physiology (Fields, Dong, Meng, & Somero, 2015; Porcelli, Butlin, Gaston, Joly, & Snook, 2015; Pörtner, Bock, & Mark, 2017; Somero, Lockwood, & Tomanek, 2017). Temperature affects developmental rate, metabolic rate, biochemical reaction kinetics, protein folding and stability, pH, and can lead to oxidative and other cell stresses.…”