Sirtuin-dependent recovery from aerial heat shock: The effects of food ration, thermal history, and sirtuin inhibition on clearance rates and valve gape activity of the California mussel, Mytilus californianus (Conrad)

Abstract

Intertidal mussels regularly experience seasonal fluctuations in food availability and heat stress over the course of a tidal cycle, yet little is known about the biochemical mechanisms linking food ration and thermal tolerance, despite evidence that food enhances stress tolerance at the organismal level. We hypothesized that sirtuins (food-dependent protein regulators of cellular homeostasis), which may regulate the cellular stress response of mytilids during heat stress, also affect organismal performance during recovery from heat stress. As part of a broader study, we investigated the effects of acclimation food ration, acclimation emersion (air) temperature, and sirtuin inhibitors on the feeding behavior of the California mussel, Mytilus californianus, during recovery from acute aerial heat shock. Mussels were acclimated for 3 wk. to either a low (0.25% algae·g mussel dry wt−1) or high (1.5% algae·g mussel dry wt−1) algal ration and low (20 °C) or high (30 °C) emersion temperatures, in tidal simulator tanks capable of maintaining standard circadian and circatidal rhythms. Following acclimation, mussels were exposed to two sirtuin inhibitors (nicotinamide and suramin) or no inhibitors for one high tide cycle. During the subsequent low tide cycle, all mussels were exposed to an acute aerial heat shock (33 °C) and then allowed to recover in their respective acclimation conditions. Every 12 h during the 48 h before sirtuin inhibition and 48 h following acute heat shock (in the corresponding high tide periods), we recorded clearance rates and valve gape activity. Mussels acclimated to a low food ration significantly reduced clearance rates with heat shock and sirtuin inhibition, but not with heat shock alone, relative to pre-treatment values regardless of emersion temperature. Mussels acclimated to a low food ration and high emersion temperature showed significant reductions in valve gape activity following an acute heat shock following sirtuin inhibition, but not in any of the other acclimation groups. Unexpectedly, heat shock alone reduced clearance rates of mussels acclimated to high food and high emersion temperatures only, without any additional effect by heat shock and sirtuin inhibition. Together, these findings suggest an important role for sirtuins at the organismal level during recovery from heat shock following acclimation to a low food ration.