(full paper is archived in the Miller Library)
Title: Temperature effects on heart rate
and valve movement in Mytilus
Student Author(s): McDonald, Laura
Faculty Advisor(s): Somero, George
Location: Final Papers Biology 175H
Date: June 2007
Abstract: When a mussel is subjected to rapidly increasing temperatures, its heart rate will sharply decrease above a critical temperature (Hcrit). Previous studies have suggested that this sudden drop in heart rate may be triggered by a behavioral adaptation to environmental stress, valve closure. This behavior would lower the amount of oxygen available for aerobic metabolism, which could necessitate a decrease in cardiac activity. My study examined the temporal patterns of heart rate and relative valve position (open versus closed) in specimens of ribbed mussel (Mytilus californianus) exposed to controlled heating in water. Heart rate data and valve motion were gathered using, respectively, impedance electrodes inserted into the pericardial space and Hall-effect sensors attached to the mussel valves. The mussels were monitored over the course of a 2.7 hour period, during which water temperature was increased from 14 degrees C to 34 degrees C. On average valves were more closed after Hcrit than before (P< 0.0001). However, valve closure began prior to Hcrit, and the mussels reached their most closed position after Hcrit had been surpassed. Thus there was no evidence that complete valve closure occurred before heart rate decline. Therefore, the fall in heart rate above Hcrit cannot be ascribed to a simple behavioral response, complete value closure. Future studies should quantify the responses of valve movement to other factors, such as decreasing water salinity and emersion effects, that are also linked to changes in mussel heart rates to gain further insight into the relationship between valve movement and heart function.