Variations in cardiac performance and heat shock protein expression to thermal stress in two differently zoned limpets on a tropical rocky shore

Understanding variation in physiological adaptations to thermal stress is vital when investigating intertidal species' distribution patterns. The thermal sensitivities of two limpets, Cellana grata and C. tore uma, differed in accordance with their vertical distributions. Cardiac performance was maintained at higher temperatures similar to 47 degrees C) for the high-zone C. grata than the mid-zone C. toreuma (similar to 42 degrees C). At 40 degrees C, C. grata maintained regular heart function for similar to 4 h, while heart function of C. toreuma decreased rapidly. Heat shock protein expression revealed that C. toreuma had two constitutive isoforms, Hsp77 and Hsp72, and C. grata one inducible form, Hsp75, which was upregulated at 40 degrees C, suggesting C. grata has a more effective heat shock response than C. toreuma. The temperature-adaptive differences in cardiac thermal tolerance and Hsp expression match observed differences in thermally induced mortalities with the onset of summer and may help predict differential effects of climate change on the two congeners.