Date of Award

Spring 2009


© 2009 Emily Zimmermann

Document Type



Marine Science

First Advisor

Philip O. Yund

Second Advisor

Markus Frederich

Third Advisor

Charles Tilburg


Populations of the gastropod Nucella lapillus are polymorphic for shell color, with light-colored shells predominating on warmer, wave-protected shores and dark-colored shells limited primarily to cooler, wave-exposed shores. During thermal stress, darker shells attain higher body temperatures than lighter shells. These results suggest that heat stress may determine field distribution patterns. However, there is currently little evidence of physiological consequences of thermal stress in these organisms. Following the guiding hypothesis that heat stress leads to cellular energy depletion, we explored whether the central energy regulator AMP-activated Protein Kinase (AMPK) is activated by heat stress. We compared this response in both color morphs to the expression of a heat shock protein (Hsp70) in field and lab experiments. For the field experiments, two color morphs of snails were tethered to a rock and exposed to heat stress on two hot summer days. For the laboratory experiments, snails were exposed to 24°C, 28°C, and 34°C using a heat lamp, and sampled after 0, 2 and 4 hours of heat stress. Samples were analyzed using western blot and quantitative real-time PCR. AMPK activity increased after 2 hours exposure to 28-30°C in dark morphs and 34°C in light morphs. In contrast, Hsp70 began to show increased mRNA expression after 4 hours at 34°C in light morphs, but no increased in Hsp70 protein was observed. Interestingly, AMPK activity had decreased again by the onset of Hsp70 expression. Our results suggest that AMPK may be an early indicator of thermal stress in gastropods and a useful tool for studying thermal stress. The delayed stress response in light morphs relative to dark morphs suggests that light morphs are more thermotolerant to higher temperatures. The predicted temperature rise due to climate change will increase stress events, possibly causing mortality in dark morphs, favoring the spread of white morphs. This change in color morph distribution may be a useful integrative indicator of climate change.


Honors thesis