Helen Gloege, a student in Mount Holyoke College, worked in the lab of Dr. Andy Davis

Abstract Daphnia and other animals face a multitude of different stressors in their daily lives. Parasites can cause various physiological changes in animals, yet few prior studies have looked at the combination of parasitism and stress in animal models. This study used Daphnia which are microscopic plankton that may have ectoparasite-like organisms attached to their surface. Vorticella, a single-celled ectoparasite, is one of these organisms that can be found attached to Daphnia. During this experiment, when Daphnia ambigua were exposed to a “stressor” the vorticella parasite led to an increased heart rate in the Daphnia. The “stressor” was made of macerated Daphnia and aimed to simulate a predation event. Daphnia without vorticella present appeared to have no discernable reaction to the stressor. While Daphnia with vorticella increase the heart rate and physiological stress reaction in Daphnia. When over twenty vorticella were present on the daphnia the heart rate continued to increase during the study period.