The importance of incorporating natural thermal variation when evaluating physiological performance in wild species

Abstract

Environmental variability in aquatic ecosystems makes the study of ectotherms complex and challenging. Physiologists have historically overcome this hurdle in the laboratory by using 'average' conditions, representative of the natural environment for any given animal. Temperature, in particular, has widespread impact on the physiology of animals, and it is becoming increasingly important to understand these effects as we face future climate challenges. The majority of research to date has focused on the expected global average increase in temperature; however, increases in climate variability are predicted to affect animals as much or more than climate warming. Physiological responses associated with the acclimation to a new stable temperature are distinct from those in thermally variable environments. Our goal is to highlight these physiological differences as they relate to both thermal acclimation and the 'fallacy of the average' or Jensen's inequality using theoretical models and novel empirical data. We encourage the use of more realistic thermal environments in experimental design to advance our understanding of these physiological responses such that we can better predict how aquatic animals will respond to future changes in our climate.

Diel cycling hypoxia enhances hypoxia-tolerance in rainbow trout (Oncorhynchus mykiss): evidence of physiological and metabolic plasticity

“…The intensifying eutrophication of freshwater systems, particularly around large urban centers (Smith, 2003), will undoubtedly increase the frequency and severity of DCH (Smith, 2003) and climate change models predict similar effects on temperatures (Caissie et al, 2014). There is also growing recognition that the response of animals to variable conditions cannot be accurately predicted based only on their response to the stable average of those conditions (Morash et al, 2018). Our current findings further underscore the necessity of incorporating environmentally relevant variability into studies examining the potential impacts of climate change on animals.…”

“…As climate change progresses, temperature and P O2 are likely to become more variable in aquatic environments (Caissie et al, 2013;Stocker et al, 2013). There is also increasing recognition that the responses of animals to variable environments differs from their responses to the mean of that variation (Morash et al, 2018). It is therefore essential to understand not only how animals will cope with static, chronic stressors, but also to variable and stochastic environments.…”

A new mesocosm system to study the effects of environmental variability on marine species and communities

“…An up-scaling from single species to the community and ecosystem level, from single to multiple driver experiments, and from short-term incubations to long-term adapted species and communities is therefore considered the logical next step (Andersson et al 2015;Riebesell and Gattuso 2015). However, a severe shortcoming of most marine studies at all levels of complexity, is the exclusion of fluctuations of abiotic (and biotic) drivers from the experimental designs (Thompson et al 2013;Boyd et al 2016;Gunderson et al 2016;Wahl et al 2016;Morash et al 2018).…”

Phenotypic plasticity in locomotor performance of a monophyletic group of weevils accords with the warmer is better hypothesis

“…Moreover, because microclimate temperatures and their variability may differ significantly from the macroclimatic setting (Woods et al, 2015;Suggitt et al, 2018), understanding of microclimatic variation may also alter expectations for particular phenotypic responses. How animals may respond under variable temperatures compared with more static settings is also not yet comprehensively understood Kingsolver and Buckley, 2017;Morash et al, 2018). Overall, therefore, it is not yet clear which of the several contrasting hypotheses to explain acclimation responses have most support, and under what conditions various forms of response might be expected.…”