Parasitic Effects of Amoebidium appalachense on Daphnia magna Heart Rate, Hopping Frequency, and Metabolic Rate

Daphnia magna are a crustacean that inhabits multiple different types of freshwater ecosystems and thus is plays a part in many different types of interspecies interactions, one of which is parasitism. Amoebidium appalachense is a Mesomycetozoean parasite of aquatic arthropods that colonizes the antenna of D. magna. Previous research has shown that A. appalachense infection will reduce the fecundity and increase mortality rate of D. magna but how it causes these effects is unknown. To determine if A. appalachense causes these effects on D. magna by either stealing nutrients inside the D. magna like a tick or by compromising D. magna’s ability to swim and find food, heart rate, hopping frequency, and metabolic rate of infected D. magna were compared to those of uninfected D. magna. I found that over the five weeks of the experiment, heart rate and hopping frequency decreased more in infected organisms than uninfected organisms. In the last three weeks of the experiment when intensity of the infection increased, the metabolic rate of the infected organisms decreased even though the metabolic rate of the uninfected increased. Interestingly, during the last three weeks of the experiment, the heart rate and hopping frequency of infected organisms did not change significantly. These results could indicate that younger organism’s heart rate and hopping frequency are more affected by the parasite, and that A. appalachense alters how it affects its host once infection intensity reaches a certain threshold.