Are reactive oxygen species always bad? Lessons from hypoxic ectotherms.

Area of Science:

• Physiology
• Biochemistry
• Environmental Science

Background:

• Oxygen is vital for aerobic metabolism but generates reactive oxygen species (ROS), impacting cellular functions from damage (oxidative distress) to signaling (oxidative eustress).
• The balance of ROS generation and scavenging is influenced by factors like oxygen availability, crucial for ectotherms.
• Hypoxia-tolerant ectotherms are thought to avoid oxidative damage, but its link to ecological fitness remains unclear.

Approach:

• This review differentiates oxidative distress and eustress, exploring their mechanistic understanding and effects on ectothermic physiology.
• It examines evidence of hypoxia-induced oxidative damage in ectotherms.
• The review discusses two potential avoidance strategies: enhanced antioxidant systems or reduced ROS generation.

Key Points:

• Ectotherms may mitigate hypoxia-induced oxidative damage by either increasing antioxidant defenses or decreasing ROS production.
• Reduced ROS generation is proposed as a more adaptable strategy for ectotherms due to metabolic variability and conflicting literature on antioxidant enzyme activity.
• Observed alterations in ROS production and oxidative status during hypoxia might serve as adaptive signaling mechanisms.

Conclusions:

• Hypoxia can induce oxidative stress in ectotherms, but adaptive strategies exist.
• Reducing ROS generation appears more advantageous for ectotherms than solely relying on antioxidant systems.
• Changes in ROS and oxidative status during hypoxia may represent an adaptive signaling mechanism for ectotherms.