Recent thermal history influences thermal tolerance in freshwater mussel species (Bivalvia: Unionoida)

Understanding species' temperature tolerances in the context of concurrent environmental stressors is critical because thermal regimes of freshwater ecosystems are changing. We evaluated the critical thermal maximum (CTM) of 3 freshwater mussel species (Alasmidonta varicosa, Elliptio complanata, and Strophitus undulatus) acclimated to 2 temperatures (15 and 25 degrees C) and exposed to 2 aeration treatments (aerated vs unaerated) during CTM testing. Responses varied by species, but mussels acclimated to 25 degrees C generally had a higher CTM than mussels acclimated to 15 degrees C. For E. complanata, the effects of acclimation temperature and aeration were interactive, such that CTM was highest at 15 degrees C but only under aerated conditions. Our results indicate that recent thermal history affects thermal tolerance, combinations of environmental stressors may influence thermal tolerance, and such responses vary among species.