Seibel, Brad [faculty advisor, Department of Biological Sciences]




squid, visual interactions hypothesis, citrate synthase, enzymes


It has been shown that the metabolic rates of deep-living species of particular pelagic groups are significantly lower than those that live closer to the surface in the water column. Various theories as to why have been presented, including the visual interactions hypothesis, which states that because there is a greatly minimized ability to visually interact in the light-limited deep, predators have a reduced need for high metabolic rates because they do not actively go after their prey. Citrate synthase is a mitochondrial enzyme found at the beginning of the citric acid cycle, which plays an integral role in cellular aerobic respiration. The products formed by the citric acid cycle go on to contribute to the electron transport chain, which produces energy for sustained activity. Due to the fact that it is the first enzyme active during the citric acid cycle, it acts as an indicator of citric acid cycle activity. Research done previously has investigated the activity of enzymes involved in the citric acid cycle, an aerobic process in different tissues of fish. The results of these experiments have shown that the activities of these enzymes decline with depth in muscle tissue. Therefore, because the highest levels of enzyme activity were seen in fish that actively go after their prey and the lowest levels of enzyme activity were in those that sit and wait for their prey to swim by, it can be inferred that the decline in enzymatic activity with depth is correlated to the greatly reduced locomotion and the more relaxed methods of feeding of organisms living in the deep. This experiment was designed to test the amount of enzymatic activity, specifically citrate synthase activity, in the brain tissue of squid living in both shallow and deep waters. It was hypothesized that there would be no difference in enzymatic activity because brain tissue is not involved in locomotion. Brain tissue samples of different species of squid were homogenized and added to a solution containing an indicator and acetyl-CoA. This solution was placed in a spectrophotometer and oxaloacetate was added. The absorbance of the reaction of oxaloacetate and acetyl-CoA, which is catalyzed by citrate synthase, was measured. It was determined that there was no significant difference in enzyme activity in the brain tissue of deep-living and shallower species. These results signify the validity of the visual interactions hypothesis, since there was no difference in enzymatic activity in tissues that are not involved in locomotion.