Abstract
The ability of an organism to alter its physiology in response to environmental conditions offers a short-term defense mechanism in the face of weather extremes resulting from climate change. These often manifest as multiple, interacting drivers, especially pH and temperature. In particular, decreased pH can impose constraints on the biological mechanisms which define thermal limits by throwing off energetic equilibrium and diminishing physiological functions (e.g., in many marine ectotherms). For many species, however, we do not have a detailed understanding of these interactive effects, especially on short-term acclimation responses. Here, we investigated the metabolic plasticity of a tropical subtidal gastropod (Trochus maculatus) to increased levels of CO2 (700 ppm) and heating (+3°C), measuring metabolic performance (Q10 coefficient) and thermal sensitivity [temperature of maximum metabolic rate (TMMR), and upper lethal temperature (ULT)]. Individuals demonstrated metabolic acclimation in response to the stressors, with TMMR increasing by +4.1°C under higher temperatures, +2.7°C under elevated CO2, and +4.4°C under the combined stressors. In contrast, the ULT only increased marginally in response to heating (+0.3°C), but decreased by −2.3°C under CO2, and −8.7°C under combined stressors. Therefore, although phenotypic plasticity is evident with metabolic acclimation, acute lethal temperature limits seem to be less flexible during short-term acclimation.
Highlights
Physiological responses to abiotic conditions, mediated by individual organisms, manifest as population- and community-level responses
Metabolic rates of the gastropods across thermal ramps were well described by the Exponentially Modified Gaussian Function, demonstrating a positive relationship with temperature up until the temperature of maximum metabolic rate (TMMR) followed by a sharp decline to lethal limits which resulted in mortality (ULT)
Elevated CO2 negatively affected the temperature coefficients (Q10 rates) of T. maculatus, with individuals exposed to elevated CO2 having Q10 values >25% lower than under ambient CO2 [two-way ANOVA, F(1, 1) = 4.3, P = 0.04, Figure 2 and Table 2]
Summary
Physiological responses to abiotic conditions, mediated by individual organisms, manifest as population- and community-level responses. CO2 Exposure Increases Thermal Sensitivity a broad range of physiological responses due to variation among and within species (Harley et al, 2017; Wang et al, 2018). Even within a species, highlights that genetic variation and variability in physiological plasticity can affect the likelihood that populations survive short-term extremes (Wang et al, 2018). Phenotypic plasticity allows organisms to respond to stressful environmental conditions and is thought to be determined by environmental selection pressure and an organism’s sensitivity to change (Parmesan and Yohe, 2003; Hoffmann and Sgró, 2011). Intertidal species generally demonstrate at least phenotypic plasticity in their thermal optima but little capability of increasing upper lethal limits (Stillman and Somero, 2000; Nguyen et al, 2011). Subtidal organisms are generally considered to live in a relatively stable environment and thought to exhibit lower plasticity but potentially a greater capacity for acclimation
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