The small body size of insects offers the opportunity of continuously monitoring the total energy metabolism of a whole population over their total life span. This results in a ''metabolic picture.'' One can then test the influence of different treatments (e.g., temperature, light program, drugs, mating, virginity) on the energy consumption. We performed such measurements with Phormia using an infrared CO2 monitoring system (URAS). Due to the restriction on carbohydrates as energy-providing substrate, the CO2 output equals the O2 input and therefore gives a true picture of energy metabolism. Thirty-five flies were placed in a respiration chamber and fed in the usual manner with sugar and water. The relatively big volume of the chamber allows unrestricted flying and walking activity. Figure 21.4 shows an example of such a measurement.
The CO2 production per 30 min was calculated from the continuous monitoring. Males and females exhibit a very different energy profile. In both sexes, however, a well-developed day-night rhythm of activity could be found. With increasing age, a decline of maximum (flight) and minimum (walking) activity can be observed. The basal metabolic rate (night values) in contrast is independent from age and is constant over the life span in males.
Different light regimes influence the adult life span. At least in Drosophila, constant light has a life-shortening effect (Sheeba et al., 2000). Under such conditions, a very high egg production rate can be observed, which might be responsible for the early death. After results from Pittendrigh (1972), the light-dark cycle under which larvae of Drosophila were reared had strong influence on the longevity of the adults. It is generally known that a desynchronization of endogenous rhythms affects many physiological parameters and is therefore of major e x x
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Metabolism. There isn’t perhaps a more frequently used word in the weight loss (and weight gain) vocabulary than this. Indeed, it’s not uncommon to overhear people talking about their struggles or triumphs over the holiday bulge or love handles in terms of whether their metabolism is working, or not.