Thermal tolerance of fish to heatwaves in agricultural streams: What does not kill you makes you stronger?

Abstract

Heatwaves are increasing in frequency and intensity under climate change. Freshwater ecosystems are among the most thermally impacted systems, within which agricultural streams are experiencing the most extreme heatwaves and deserve prioritised focus. Heatwaves are approaching the upper thermal limits of many fishes but have received little attention to date. To study whether and how fish tolerate heatwaves from a physiological perspective, we simulated single, multiple, and extended heatwaves at 32 and 34°C in the laboratory, based on high‐resolution summer temperatures recorded in agricultural versus forested streams in Illinois, U.S.A. By investigating the effects of heatwaves on 25°C acclimated fathead minnow Pimephales promelas, an important prey species across North America, we witnessed its high thermal resilience, including a rapid return to metabolic homeostasis after single and multiple heatwaves, measured by oxygen consumption rate. During an extended heatwave, fathead minnow were still able to partially lower oxygen consumption rate after the initial exposure. We also found transient increases in their critical thermal maximum, especially after higher intensity and frequency of heatwaves. However, the thermal resilience of fathead minnow did come with costs, including reduced anaerobic capacity indicated by decreased lactate dehydrogenase activity and impaired antioxidant defence indicated by reduced superoxide dismutase in white muscle. By monitoring metabolic costs and physiological adjustments of fish during and after heatwaves, we showed that fathead minnow were resilient to simulated current and near‐future heatwaves, which may allow them to cope with thermal extremes expected in agricultural streams. Overall, the real‐time monitoring of fish responses to heatwaves incorporates natural dynamics of thermal patterns. It facilitates mechanistic understandings of how fish react to thermal challenges in the real world and offers opportunities to incorporate high‐resolution metabolic costs into future bioenergetic modelling.

Role of climatic variability in shaping intraspecific variation of thermal tolerance in Mediterranean water beetles

“…, 2018; Dai et al. , 2022). Empirical research has demonstrated that extreme events can drive directional selection toward more resistant phenotypes (Pauls et al.…”

“…As for the differences in acclimation capacity between the populations of the hydrophilid species studied, they might be related to the higher intensity and frequency of extreme events with ongoing climate change, such as heat waves, which could have an impact on the plasticity of the upper thermal limit at the micro-evolutionary level (Baudier et al, 2018;Dai et al, 2022). Empirical research has demonstrated that extreme events can drive directional selection toward more resistant phenotypes (Pauls et al, 2013; and cause a loss of genetic diversity (e.g., Gurgel et al, 2020).…”

Thermal tolerance in an extremophile fish from Mexico is not affected by environmental hypoxia

“…Anthropogenic global warming may lead to seasonal temperature increases by up to 4°C by 2100, along with an increase in the frequency of localized acute and extreme warming events ( Comte and Olden, 2017 ; Bierbach et al, 2022 preprint). These changes are likely to cause population declines, or even extinction of species that are poorly adapted to cope with these novel environmental conditions ( Pacifici et al, 2015 ; Dai et al, 2022 ). A key trait and a critical factor for survival in this regard is an organism's ability to survive and function within a specific temperature range, which is referred to as thermal tolerance.…”

“…critical thermal limits, CT min and CT max , ( Beitinger and Lutterschmidt, 2011 )], although growth and reproduction may require a narrower range thus higher minima and lower maxima ( Pörtner, 2001 ; Burleson and Silva, 2011 ; Illing et al, 2020 ). Understanding how organisms deal with increased or even extreme temperature regimes that will become more frequent becomes crucial for predicting the effects of climate change on populations and species, and ultimately may help to take suitable measures and actions to counteract local population declines or extinction events ( Dai et al, 2022 ; Earhart et al, 2022 ; Desforges et al, 2023 ).…”

“…These effects at the biochemical level cascade up to affect processes across levels of biological organization, with profound effects on complex physiological processes, such as cardiovascular function, muscle contraction, metabolism, energy budgets, which impact organismal growth and performance as well as thermal and hypoxia tolerance ( McBryan et al, 2013 ; Little et al, 2020 ; Ern et al, 2023 ). Since chronic extreme conditions as well as periodic extreme thermal events are predicted to become more common also in yet normal habitats, the combination of high temperature and hypoxia in the environment can become particularly devastating as reports of heat-related mass die-offs of fishes and other higher aquatic organisms are further increasing in frequency ( Dai et al, 2022 ). For example, the mass mortality events known as ‘summerkill’ that occur in lakes in the north-temperate zone, due to relatively transient episodes of high temperature and low oxygen, are predicted to increase more than fourfold by 2100 ( Till et al, 2019 ).…”