Thermal tolerance and routine oxygen consumption of convict cichlid, Archocentrus nigrofasciatus, acclimated to constant temperatures (20 °C and 30 °C) and a daily temperature cycle (20 °C → 30 °C)
Cooper, Cassidy; Eme, John; Kristan, William (2021), Thermal tolerance and routine oxygen consumption of convict cichlid, Archocentrus nigrofasciatus, acclimated to constant temperatures (20 °C and 30 °C) and a daily temperature cycle (20 °C → 30 °C), Dryad, Dataset, https://doi.org/10.25338/B8CG94
Organismal temperature tolerance and metabolic responses are correlated to recent thermal history, but responses to thermal variability are less frequently assessed. There is great interest in whether organisms that experience greater thermal variability can gain metabolic or tolerance advantages through phenotypic plasticity. We compared thermal tolerance and routine aerobic metabolism of Convict cichlid acclimated for 2 weeks to constant 20°C, constant 30°C, or a daily cycle of 20→30°C (1.7°C/hr). Acute routine mass-specific oxygen consumption (Ṁo 2 ) and Critical Thermal Maxima/Minima (CTMax/CTMin) were compared between groups, with cycle acclimated fish sampled from the daily minimum (20°C, 0900 hrs) and maximum (30°C, 1600 hrs). Cycle-acclimated fish demonstrated statistically similar CTMax at the daily minimum and maximum (39.0°C, 38.6°C) but distinct CTMin values, with CTMin 2.4°C higher for fish sampled from the daily 30°C maximum (14.8°C) compared to the daily 20°C minimum (12.4°C). Measured acutely at 30°C, Ṁo 2 decreased with increasing acclimation temperature; 20°C acclimated fish had an 85% higher average Ṁo 2 than 30°C acclimated fish. Similarly, acute Ṁo 2 at 20°C was 139% higher in 20°C acclimated fish compared to 30°C acclimated fish. Chronic Ṁo 2 was measured in separate fish continually across the 20→30°C daily cycle for all 3 acclimation groups. Chronic Ṁo 2 responses were very similar between groups between average individual hourly values, as temperatures increased or decreased (1.7°C/hr). Acute Ṁo 2 and thermal tolerance responses highlight “classic” trends, but dynamic, chronic trials suggest acclimation history has little effect on the relative change in oxygen consumption during a thermal cycle. Our results strongly suggest that the minimum and maximum temperatures experienced more strongly influence fish physiology, rather than the thermal cycle itself. This research highlights the importance of collecting data in both cycling and static (constant) thermal conditions, and further research should seek to understand whether ectotherm metabolism does respond uniquely to fluctuating temperatures.