Influence of temperature and activity on the metabolic rate of adult Drosophila melanogaster

We measured metabolic rates of adult male Drosophila melanogaster allowed to evolve in the laboratory at 18 and 25°C and compared these with measurements of metabolic rates of flies collected along a latitudinal gradient in Australia. Metabolic rates of flies that had evolved in the laboratory at low temperature were 5–7% higher than those of flies allowed to evolve at high temperature. Metabolic rates of field collected increased with latitude when measured at 18°C but not at higher temperature (25°C) and were about 9% greater in high latitude (∼41′00) flies than low latitude (16′53) flies. Metabolic rate was strongly influenced by measurement temperature; estimated Q₁₀s ranged from 1.79 to 2.5 for measurements made at 18 and 25°C. Metabolic rate scaled isometrically with body mass; the estimated slope of a ln-ln regression of metabolic rate and body mass was 1.03 ± 0.1. We used our measures of metabolic rate and activity to estimate the minimum cost of transport (MCOT) while walking. The estimates of MCOT have high standard errors (lab, 34.30 ± 14.2 ml O₂/g/km; and field, 38.0 ± 17.0 ml O₂/g/km); however, they differ by only 3–9% from predicted values based on allometric relationships reported in the literature.