Effects of temperature on responses to anoxia and oxygen reperfusion in Drosophila melanogaster

Insects in general, and Drosophila in particular, are much more capable of surviving anoxia than vertebrates, and the mechanisms involved are of considerable biomedical and ecological interest. Temperature is likely to strongly affect both the rates of damage occurring in anoxia and the recovery processes in normoxia, but as yet there is no information on the effect of this crucial variable on recovery rates from anoxia in any animal. We studied the effects of temperature, and thus indirectly of metabolic flux rates, on survival and recovery times of individual male Drosophila melanogaster following anoxia and O2 reperfusion. Individual flies were reared at 25° and exposed to an anoxic period of 7.5, 25, 42.5 or 60?min at 20, 25 or 30°. Before, during and after anoxic exposure the flies' metabolic rates (MRs), rates of water loss and activity indices were recorded. Temperature strongly affected the MR of the flies, with a Q10 of 2.21. Temperature did not affect the slope of the relationship between time to recovery and duration of anoxic exposure, suggesting that thermal effects on damage and repair rates were similar. However, the intercept of that relationship was significantly lower (i.e. recovery was most rapid) at 25°, which was the rearing temperature. When temperatures during exposure to anoxia and during recovery were switched, recovery times matched those predicted from a model in which the accumulation and clearance of metabolic end-products share a similar dependence on temperature. ©2011. Published by The Company of Biologists Ltd.Fil:Schilman, P.E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Scaling of insect metabolic rate is inconsistent with the nutrient supply network model

1. The nutrient supply network model of the metabolic theory of ecology predicts that metabolic rate scales as mass0.75 at all hierarchical levels. 2. An alternative, cell size, model suggests that the scaling of metabolic rate is a by-product of the way in which body size changes, by cell size or number, or some combination thereof. It predicts a scaling exponent of mass0.75 at the widest interspecific level, but values of mass 0.67-1.0 for lower taxonomic groups or within species. 3. Here these predictions are tested in insects using 391 species for the interspecific analysis, and the size-polymorphic workers of eight ant species at the intraspecific level. In the latter, the contribution of ommatidium size and number to variation in body length, which is closely related to eye size, is used to assess the relative contributions of changes in cell size and number to variation in body size. 4. Before controlling for phylogeny, metabolic rate scaled interspecifically as mass0.82. Following phylogenetic correction, metabolic rate scaled as mass0.75. 5. By contrast, the intraspecific scaling exponents varied from 0.67 to 1.0. Moreover, in the species where metabolic rate scaled as mass1.0, cell size did not contribute significantly to models of body size variation, only cell number was significant. Where the scaling exponent was < 1.0, cell size played an increasingly important role in accounting for size variation. 6. Data for one of the largest groups of organisms on earth are therefore inconsistent with the nutrient supply network model, but provide support for the cell size alternative. © 2007 The Authors.Articl

Do insect metabolic rates at rest and during flight scale with body mass?

Energetically costly behaviours, such as flight, push physiological systems to their limits requiring metabolic rates (MR) that are highly elevated above the resting MR (RMR). Both RMR and MR during exercise (e.g. flight or running) in birds and mammals scale allometrically, although there is little consensus about the underlying mechanisms or the scaling relationships themselves. Even less is known about the allometric scaling of RMR and MR during exercise in insects. We analysed data on the resting and flight MR (FMR) of over 50 insect species that fly to determine whether RMR and FMR scale allometrically. RMR scaled with body mass to the power of 0.66 (M(0.66)), whereas FMR scaled with M(1.10). Further analysis suggested that FMR scaled with two separate relationships; insects weighing less than 10 mg had fourfold lower FMR than predicted from the scaling of FMR in insects weighing more than 10 mg, although both groups scaled with M(0.86). The scaling exponents of RMR and FMR in insects were not significantly different from those of birds and mammals, suggesting that they might be determined by similar factors. We argue that low FMR in small insects suggests these insects may be making considerable energy savings during flight, which could be extremely important for the physiology and evolution of insect flight

Scaling of gas exchange cycle frequency in insects

Previously, it has been suggested that insect gas exchange cycle frequency (fC) is mass independent, making insects different from most other animals where periods typically scale as mass−0.25. However, the claim for insects is based on studies of only a few closely related taxa encompassing a relatively small size range. Moreover, it is not known whether the type of gas exchange pattern (discontinuous versus cyclic) influences the fC–mass scaling relationship. Here, we analyse a large database to examine interspecific fC–mass scaling. In addition, we investigate the effect of mode of gas exchange on the fC–scaling relationship using both conventional and phylogenetically independent approaches. Cycle frequency is scaled as mass−0.280 (when accounting for phylogeneticnon-independence and gas exchange pattern), which did not differ significantly from mass−0.25. The slope of the fC–mass relationship was shallower with a significantly lower intercept for the species showing discontinuous gas exchange than for those showing the cyclic pattern, probably due to lower metabolic rates in the former. Insects therefore appear no different from other animals insofar as the scaling of gas exchange fC is concerned, although gas exchange fC may scale in distinct ways for different patterns