Dramatic changes in mitochondrial substrate use at critically high temperatures: a comparative study using Drosophila

Area of Science:

• Physiology
• Biochemistry
• Ecology

Background:

• Ectotherm thermal tolerance is crucial for species distribution but poorly understood.
• Mitochondrial function may be a key factor, with impaired oxidative phosphorylation (OXPHOS) linked to heat sensitivity in insects.

Purpose of the Study:

• To investigate the physiological basis of heat tolerance in *Drosophila* species.
• To determine how temperature affects mitochondrial function, specifically oxidative phosphorylation (OXPHOS) and substrate oxidation.

Main Methods:

• High-resolution respirometry was used to measure mitochondrial oxygen consumption rates in six *Drosophila* species.
• A substrate-uncoupler-inhibitor titration protocol assessed electron transport system function across a range of temperatures.

Main Results:

• Complex I-supported OXPHOS (CI-OXPHOS) decreased significantly at higher temperatures (34-46°C).
• Maximal OXPHOS capacity was maintained through alternative substrate oxidation (proline, succinate, glycerol-3-phosphate), indicating mitochondrial flexibility.
• The temperature at which CI-OXPHOS failed correlated with species' heat tolerance.

Conclusions:

• Mitochondrial flexibility allows *Drosophila* to maintain maximal OXPHOS capacity above organismal heat limits.
• The failure of CI-OXPHOS at high temperatures is a key physiological indicator of heat tolerance.
• Further research is needed to understand the mechanisms behind CI-OXPHOS perturbation and its impact on ATP production.