Abstract:
Temperature is a key factor that impacts all levels of organization. Minute shifts away from thermal optima results in detrimental effects that impact growth, reproduction & survival. Poikilothermic species are especially prone to temperature shifts as their body temperature closely matches that of the environment. Metabolic rates are sensitive to temperature and for organism exposed to high acute temperature, particularly intertidal ectotherms, energetic processes are negatively impacted. Previous investigations looking at acute heat stress implicate mitochondrial dysfunction in thermal tolerance and it is argued that the heart sets the upper thermal limits for species. The brain is, by weight, one of the most metabolically active and arguably the most temperature sensitive organ in the body. It is highly aerobic and as a result nearly entirely reliant on oxidative phosphorylation to meet energetic demands. As temperature rises mitochondria become less efficient at synthesising adequate amounts of ATP to meet the increasing demands leading to an energetic crisis. Using brain homogenates of three closely related triplefin species (Bellapiscis medius, Forsterygion lapillum, and Forsterygion varium) respiration and ATP dynamics were assessed at three temperatures (15, 25, and 30°C). It was found that at 30°C all species showed significant decreases in mitochondrial function. While B. medius maintained efficient OXPHOS at high temperatures. The balance of energetic supply and demand was disrupted in all three species at 30°C and only the intertidal B. medius maintained a high P/O at 30°C compared with F. lapillum and F. varium. These results showed that brain mitochondria become less efficient at temperatures below their respective CTmax and may play a significant role in thermal tolerance limits