Effects of Simulated Heat Wave on Oxidative Physiology and Immunity in Asian Yellow Pond Turtle (Mauremys mutica)

Abstract

Global warming has led to an increase in the frequency, duration, and intensity of heat waves in the summer, which can cause frequent and acute heat stress on ectotherms. Thus, determining how ectothermic animals respond to heat waves has been attracting growing interest among ecologists. However, the physiological and biochemical responses to heat waves in reptiles, especially aquatic reptiles, are still poorly understood. The current study investigated the oxidant physiology, immunity, and expression levels of heat shock proteins (HSP) mRNA after exposure to a simulated heat wave (1 week, 35 ± 4°C), followed by a recovery period (1 week, 28 ± 4°C) in juvenile Asian yellow pond turtle (Mauremys mutica), a widely farmed aquatic turtle in East Asia. The contents of malondialdehyde (MDA) in the liver and muscle were not significantly affected by the heat wave or recovery. Of all antioxidant enzymes, only the activity of glutathione peroxidase (GSH-Px) in muscles increased after heat wave, while the total superoxide dismutase (T-SOD), catalase activity (CAT), and total antioxidant capacity (T-AOC) did not change during the study. The organo-somatic index for the liver and spleen of M. mutica decreased after the heat wave but increased to the initial level after recovery. In contrast, plasma lysozyme activity and serum complement C4 levels increased after the heat wave, returning to the control level after recovery. In addition, heat waves did not alter the relative expression of HSP60, HSP70, and HSP90 mRNA in the liver. Eventually, heat wave slightly increased the IBR/n index. Therefore, our results suggested that heat waves did not lead to oxidative damage to lipids in M. mutica, but deleteriously affected the turtles’ immune organs. Meanwhile, the constitutive levels of most antioxidative enzyme activities, HSPs and enhanced blood immune functions might protect the turtles from the threat of heat waves under the current climate scenarios.

Influence of High Temperatures and Heat Wave on Thermal Biology, Locomotor Performance, and Antioxidant System of High-Altitude Frog Nanorana pleskei Endemic to Qinghai-Tibet Plateau

“…Similar results were found in P. guttatus in the acclimation to simulated heat wave, in which the antioxidative capacity did not change but the oxidative damage level obviously decreased (Stahlschmidt et al, 2017). On the contrary, although the activity of T-SOD and CAT, and T-AOC are not affected by heat wave, the GPX activity in the muscle in M. mutica significantly increased (Li et al, 2021). The activities of antioxidant enzymes were attenuated for N. pleskei in the acclimation to simulated heat wave, but its oxidative damage level dramatically decreased.…”

“…However, the telomere length and overwinter survival of desert toad-headed agama (Phrynocephalus przewalskii) were shortened after exposure to a stimulated heat wave (Zhang et al, 2018). In Asian yellow pond turtle (Mauremys mutica), heat wave does not significantly affect the level of MDA in the liver and muscle (Li et al, 2021). Therefore, heat wave has different physiological effects on different species, positive or negative.…”

Heat wave induces oxidative damage in the Chinese pond turtle (Mauremys reevesii) from low latitudes

“…The antioxidant defense may be the most important physiological adjustment when animals are exposed to heat waves (Troschinski et al, 2014;Baker et al, 2020). Extremely high temperatures would seriously increase the metabolic rates and synchronously produce reactive oxygen species (ROS;Ben Ameur et al, 2012), which would react with the molecular components of cells, such as lipids, proteins, and nucleic acids, leading to oxidative damage in cell machinery, indicated by the content of malondialdehyde (MDA), carbonylated protein, and DNA injury (Li et al, 2021). The accumulation of oxidative damage then induces the collapse of functions such as immunity, and even leads to mortality of the individuals; hence, depressed immunity can serve as a proxy for oxidative damage.…”

“…In summary, heat waves induce oxidative damage (e.g., MDA) and affect immunity; however, individuals can enhance their antioxidant defense to reduce the potential threat of heat waves (Speakman and Garratt, 2014). For example, our previous study demonstrated that when yellow pond turtles (Mauremys mutica) faced heat waves, enhanced GPx facilitated antioxidant defense and plausibly reduced the production of MDA (i.e., oxidative damage), thereby sustaining innate immunity, including increased lysozyme activity and serum complement C4 levels (Li et al, 2021).…”

“…The latitudinal vulnerability of animals to heat waves is determined by the interaction between heat waves and how local animals physiologically resist them (Hall and Sun, 2021). Therefore, revealing the physiological resistance to heat waves across latitudes is critical for understanding the thermal adaptation to environments and for evaluating the vulnerability of animals to climate warming geographically (Carlo et al, 2018;Dahlke et al, 2020;Li et al, 2021).…”