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

Shuran Li,Yongpu Zhang,Zhiwang Xu,Lei Xie,Wei Chen,Jinhuan Li

doi:10.3389/fevo.2021.704105

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.

Highlights

The global average air temperature has increased by approximately 0.85◦C over the past century and may increase by a further 0.3–4.8◦C by the end of this century (IPCC, 2014)
The current study demonstrated that the effects of a simulated heat wave on the biochemistry and physiology of the aquatic turtle M. mutica were complex and transient
After exposure to a 1-week heat wave, no significant oxidative damage was found, and only GSH-Px activity of the antioxidant indices was enhanced in M. mutica

Summary

INTRODUCTION

The global average air temperature has increased by approximately 0.85◦C over the past century and may increase by a further 0.3–4.8◦C by the end of this century (IPCC, 2014). Many studies have exposed animals to different acute constant temperature heat waves, which neglects the diurnal fluctuations in temperature under natural conditions (Dittmar et al, 2014; Leicht et al, 2019). This lack of ecological relevance may lead to misleading interpretations, as the performance of ectotherms is not always identical under constant and fluctuating thermal conditions (Bozinovic et al, 2011; Moore et al, 2021). We conducted an experiment in M. mutica to reveal the effects of heat waves on its antioxidant responses, immune function, and gene expression. We predicted that heat waves would induce oxidative stress and depress immune function in M. mutica, whereas antioxidant capacity and expression of HSPs would be enhanced to protect M. mutica from heat waves

Experimental Procedure

RESULTS

DISCUSSION