Interactions between Mycophagous Drosophila and Their Nematode Parasites: From Physiological to Community Ecology

Abstract

Although community-level effects of parasites have been documented where parasites invade new areas, there is relatively little information on such effects in natural host-parasite systems. The present study examines how an indigenous parasitic nematode, Howardula aoronymphium, may affect the structure of mycophagous Drosophila communities in eastern North America. A field-cage experiment demonstrated that the competitive superiority of Drosophila putrida over Drosophila falleni was diminished by the parasites. This probably results from D. putrida being more severely affected than D. falleni by the parasites. Across the eastern United States, the relative abundance of D. putrida is much greater in areas where H. aoronymphium is absent. The geographical distribution of H. aoronymphia appears to be governed largely by temperature, occurring only north of the 27°C isotherm of mean July temperature. In the laboratory, growth and reproduction of nematodes is arrested at 29°C, and transmission rates drop to zero at 27°C and above. Because potential hosts are abundant in the southern United States, the absence of H. aoronymphium from this region is most likely due to its intolerance of high temperature. These results suggest that the physiological ecology of a parasitic nematode contributes to geographical variation in the relative abundance of its host species