The effects of temperature on heart rate redox state and metabolic reserves of chiton species

Abstract

Temperature is an essential factor that affects all levels of biological organisation. A move towards thermal optimum can negatively change growth, reproduction, and survival. Polyplacophora is particularly susceptible to temperature change as its internal temperature closely matches that of the environment. Metabolic processes are sensitive to temperature, thus energetic processes of organisms are negatively impacted if exposed to extreme temperatures. Previous work has suggested that the heart sets the upper thermal limits of species. However, with increased temperature, mitochondria become less efficient at producing adequate ATP to meet increasing demands, leading to a setback in ATP supply and demand. This suggests that mitochondrial dysfunction may be a limiting factor in acute heat stress. Mitochondrial fluorescence and heart function of three closely related chiton species (Sypharochiton pelliserpentis, Chiton glaucus, and Ischnochiton maorianus) were assessed at increasing temperatures (20°C - 40°C). It was found that at 22°C, there was a decrease in mitochondrial function for subtidal I. maorianus. In comparison, subtidal C. glaucus and intertidal S. pelliserpentis maintained mitochondrial demand at high temperatures. Disruption in heart function was evident from 32°C in subtidal I. maorianus and C. glaucus. These results showed that heart and mitochondrial function significantly affect thermal tolerance limits and can be species-dependent. The mitochondria manage metabolite-producing pathways required for survival and reproduction, thus mitochondrial metabolites influence the thermal sensitivity of species. Mitochondrial metabolites of all species were assessed at high temperatures (30°C) to determine biochemical limitations in acute thermal stress. It was found that metabolic capacity is increased at 30° for intertidal, S. pelliserpentis, compared to subtidal, C. glaucus and I. maorianus. These results showed that mitochondrial metabolites provide further insight into mitochondrial function at increased temperature. Key Words: Thermal Tolerance, Mitochondria, Heart, Polyplacophora