High-Precision Calorimetry-Based Analysis of Pupal-Pharate Adult Development in Drosophila melanogaster.

In holometabolous insects, the larval body is almost completely decomposed and reconstructed into the adult body during the pupal-pharate adult stages. Therefore, the total energetic cost of this process is a key thermodynamic quantity necessary for evaluating the benefit of their life history. Here, we measured whole-body thermal dissipation of single pupae of the fruit fly, Drosophila melanogaster, during the period from puparium formation to adult eclosion as a function of age, using a high-precision isothermal calorimeter at T = 298 K. The mass-specific energy consumption during the period from the onset of larval-pupal apolysis to adult eclosion was determined to be 2.3 kJ/g for an individual of mass (adult) = 1.0 mg, while it was observed to follow Kleiber's law for individuals smaller than mass (adult) = 1.0 mg. During the pupal-pharate adult period, in addition to the U-shaped variation, several characteristic thermal dissipations related to various events, including somatic muscle contractions, ecdyses, pulsatile hormone secretion in a pharate adult, and vaporization of the exuvial fluid, were observed. The periodic bursts in the pharate adult stage grew exponentially, suggesting that the positive feedback in the metabolic system synchronized with the progression of development, making the energy consumption in this stage more efficient. The present study showed that high-precision calorimetry is a powerful and credible method for measuring not only the total energy spent during development but also the energy spent during every specific developmental event in an organism.

Temperature-independent energy expenditure in early development of the African clawed frog Xenopus laevis.

The thermal dissipation of activated eggs and embryos undergoing development from cleavage to the tailbud stage of the African clawed frog Xenopus laevis was measured as a function of incubation time at temperatures ranging from T = 288.2 K to 295.2 K, using a high-precision isothermal calorimeter. A23187-mediated activation of mature eggs induced stable periodic thermal oscillations lasting for 8-34 h. The frequency agreed well with the cell cycle frequency of initial cleavages at the identical temperature. In the developing embryo, energy metabolism switches from embryonic to adult features during gastrulation. The thermal dissipation after gastrulation fit well with a single modified Avrami equation, which has been used for modeling crystal-growth. Both the oscillation frequency of the activated egg and the growth rate of the embryo strongly depend on temperature with the same apparent activation energy of approximately 87 kJ mole(-1). This result suggests that early development proceeds as a single biological time, attributable to a single metabolic rate. A temperature-independent growth curve was derived by scaling the thermogram to the biological time, indicating that the amount of energy expenditure during each developmental stage is constant over the optimal temperature range.

Energy budget of Drosophila embryogenesis.

Eggs of oviparous animals must be prepared to develop rapidly and robustly until hatching. The balance between sugars, fats, and other macromolecules must therefore be carefully considered when loading the egg with nutrients. Clearly, packing too much or too little fuel would lead to suboptimal conditions for development. While many studies have measured the overall energy utilization of embryos, little is known of the identity of the molecular-level processes that contribute to the energy budget in the first place [1]. Here, we introduce Drosophila embryos as a platform to study the energy budget of embryogenesis. We demonstrate through three orthogonal measurements - respiration, calorimetry, and biochemical assays - that Drosophila melanogaster embryogenesis utilizes 10 mJ of energy generated by the oxidation of the maternal glycogen and triacylglycerol (TAG) stores (Figure 1). Normalized for mass, this is comparable to the resting metabolic rates of insects [2]. Interestingly, alongside data from earlier studies, our results imply that protein, RNA, and DNA polymerization require less than 10% of the total ATPs produced in the early embryo.

Mixing schemes in a urea-H2O system: a differential approach in solution thermodynamics.

The excess partial molar enthalpies of urea (UR), H U R (E ), were experimentally determined in UR-H 2O at 25 degrees C. The H U R (E ) data were determined accurately and in small increments in the mole fraction of UR, x U R , up to x U R approximately 0.22. Hence it was possible to evaluate one more x U R -derivative graphically without resorting to any fitting function, and the model-free UR-UR enthalpic interaction, H U R- U R (E ), was calculated. Using previous data for the excess chemical potential, mu U R (E ), the entropy analogue, S U R- U R (E ), was also calculated. The x U R -dependences of both H U R- U R (E ) and S U R- U R (E ) indicate that there is a boundary at x U R approximately 0.09 at which the aggregation nature of urea changes. From the results of our earlier works, we suggest that a few UR molecules aggregate at x U R approximately 0.09, while the integrity of H 2O is retained at least up to x U R approximately 0.20. Together with the findings from our previous studies, we suggest that in the concentration range x U R < 0.22, UR or its aggregate form hydrogen bonds to the H 2O network, reducing the degree of fluctuation characteristic to liquid H 2O. However, up to at least x U R = 0.20 the hydrogen bond network remains intact. Above x U R approximately 0.22, the integrity of H 2O is likely be lost. Thus, in discussing the effect of urea on H 2O and in relating it to the structure and function of biopolymers in aqueous solutions, the concentration region in question must be specified.