Mytilus californianus regularly experiences fluctuations in temperature and food availability during periods of exposure within a tidal cycle. Previous research has shown that diet and thermal history influence the ability of mussels to tolerate heat stress, which may in part be regulated by sirtuins, a class of NAD-dependent deacetylases involved in the control and removal of reactive oxygen species. To test the interactions of sirtuins, diet, and heat stress, we monitored siphon activity (a direct proxy for feeding activity) of mussels acclimated to varying thermal and dietary conditions. Mussels were acclimated to either ambient (20°C) or warm (30°C) air temperatures and fed a low or high diet (0.25% and 1.5% algae·g mussel dry wt-1·day-1, respectively) for 3 weeks. Half of the mussels were exposed to nicotinamide and suramin, two sirtuin inhibitors, following acclimation. All mussels were then exposed to an acute heat shock (33°C) during a low tide cycle. We recorded siphon activity during submersion for 48 h before and after inhibition and heat shock. Videos were analyzed using ImageJ to estimate percent time the siphons were exposed. We used a non-linear mixed effects model to determine the effects of acclimation, heat shock, and sirtuin inhibition on siphon activity.
Results/Conclusions
Following heat shock, sirtuin inhibition significantly reduced siphon activity (p=0.001), and the percent of time spent filtering increased at night (p=0.04). There were no statistically significant effects of food and temperature acclimation conditions, though these have had a documented impact in previous siphon opening studies. Sirtuin activity appeared to be an integral part of recovery following heat shock, which supports our hypothesis that these proteins play a vital role in the Mytilus stress response. Diurnal patterns in feeding activity only emerged after acute heat shock, which may support results seen in previous studies that sirtuin activity varies diurnally. Understanding this response and the drivers behind it will be integral to understanding the intertidal community as a whole, especially as the effects of climate change intensify. Anthropogenic climate change is causing an increase in average temperatures, a decrease in food availability, and an increase in the frequency of acute heat stress events. By better understanding the mechanistic processes driving this organism’s response to multiple stressors, and the role acclimation plays in this, we can determine how intensely this foundational species will be impacted by climate change.