Temperature Tolerance in Three Mycophagous Drosophila Species: Relationships with Community Structure

Patterns of host use at several spatial and temporal scales suggest that temperature tolerance may influence the structure of mycophagous fly communities. For instance, Drosophila putrida is more abundant than D. falleni and D. tripunctata in dry sites, at dry periods, and in small, desiccation-prone mushrooms. In this experiment, we acclimated flies from these species at different temperatures (15°C, 20°C, 25°C, and 30°C) for 5 d, and then measured their responses to acute thermal stress (increasing temperature 0.5°C/min). ANOVA were used to describe the effects of sex, species, and acclimation temperature on: 1) survivorship after 5 d, and 2) Critical Thermal Maxima (CTMax). Critical Thermal Maximum was measured as the temperature at which 50% of the flies in a sample were incapable of righting themselves. Survivorship was uniformly high for all species from 15°C to 25°C. However, at 30°C, D. putrida survival (74%) was significantly higher than either D. falleni (39%) or D. tripunctata (23%). When averaged across all acclimation temperatures, D. putrida also had a higher CTMax than the other species (40.7°C, compared to 40.2°C for D. falleni and 39.9°C for D. tripunctata). D. putrida was the only species with a CTMax that increased significantly after acclimation at 30°C. Thus, D. putrida was more tolerant to chronic and acute thermal stress than the other species, and was the only species to show an adaptive physiological response to high temperature exposure. These species differences are consistent with spatial and temporal abundance patterns, and may contribute to patterns in community structure.