Relationships between protein supplies and B-vitamin requirements, in axenically cultured Drosophila

Regulation of Body Size and Growth Control

The control of body and organ growth is essential for the development of adults with proper size and proportions, which is important for survival and reproduction. In animals, adult body size is determined by the rate and duration of juvenile growth, which are influenced by the environment. In nutrient-scarce environments in which more time is needed for growth, the juvenile growth period can be extended by delaying maturation, whereas juvenile development is rapidly completed in nutrient-rich conditions. This flexibility requires the integration of environmental cues with developmental signals that govern internal checkpoints to ensure that maturation does not begin until sufficient tissue growth has occurred to reach a proper adult size. The Target of Rapamycin (TOR) pathway is the primary cell-autonomous nutrient sensor, while circulating hormones such as steroids and insulin-like growth factors are the main systemic regulators of growth and maturation in animals. We discuss recent findings in Drosophila melanogaster showing that cell-autonomous environment and growth-sensing mechanisms, involving TOR and other growth-regulatory pathways, that converge on insulin and steroid relay centers are responsible for adjusting systemic growth, and development, in response to external and internal conditions. In addition to this, proper organ growth is also monitored and coordinated with whole-body growth and the timing of maturation through modulation of steroid signaling. This coordination involves interorgan communication mediated by Drosophila insulin-like peptide 8 in response to tissue growth status. Together, these multiple nutritional and developmental cues feed into neuroendocrine hubs controlling insulin and steroid signaling, serving as checkpoints at which developmental progression toward maturation can be delayed. This review focuses on these mechanisms by which external and internal conditions can modulate developmental growth and ensure proper adult body size, and highlights the conserved architecture of this system, which has made Drosophila a prime model for understanding the coordination of growth and maturation in animals.

Gut microbiota dictates the metabolic response of Drosophila to diet

Animal nutrition is profoundly influenced by the gut microbiota, but knowledge of the scope and core mechanisms of the underlying animal-microbiota interactions is fragmentary. To investigate the nutritional traits shaped by the gut microbiota of Drosophila, we determined the microbiota-dependent response of multiple metabolic and performance indices to systematically varied diet composition. Diet-dependent differences between Drosophila bearing its unmanipulated microbiota (conventional flies) and experimentally deprived of its microbiota (axenic flies) revealed evidence for: microbial sparing of dietary B vitamins, especially riboflavin, on low-yeast diets; microbial promotion of protein nutrition, particularly in females; and microbiota-mediated suppression of lipid/carbohydrate storage, especially on high sugar diets. The microbiota also sets the relationship between energy storage and body mass, indicative of microbial modulation of the host signaling networks that coordinate metabolism with body size. This analysis identifies the multiple impacts of the microbiota on the metabolism of Drosophila, and demonstrates that the significance of these different interactions varies with diet composition and host sex.

Nutritional requirements of inbred lines and crosses ofDrosophila melanogaster

1. The problem of whether or not hybrids are more efficient, less variable and have less stringent nutritional needs than their parents is examined by finding the dose-responses of four inbredDrosophilalines and their crosses to casein, choline, RNA, riboflavine, nicotinic acid, pyridoxine and folic acid, under germ-free conditions.

2. Under more or less optimal conditions, survival, development rate and weight of the hybrids are generally superior to those of the inbreds; the 4-way cross is not inferior to the 2-way crosses. Variability of the crosses is not necessarily lower than that of the inbreds, and the 4-way cross is no more variable than the 2-way crosses.

3. As measured by growth rate, the hybrids use casein more effectively than the pure lines, but their relative efficiency declines as the casein supply is decreased. There is a positive correlation between casein requirements for optimal growth and minimum requirements of pyridoxine. Hybrids also tend to be more efficient in their use of choline, but not of the other nutrients examined.

4. Deficiencies of particular nutrients (and also of excess provision of the non-vitamins) affect the lines and crosses differently, so that their relationships to one another are altered. The hybrids show no special advantage in resisting departures from the optimum. Variability is also changed significantly under sub-optimal conditions and, in some situations, the hybrids may then be more variable than the inbreds.

5. Each line and each cross is found to have its own optimal nutritional environment, and its particular reactions to departure from this. The full potential of the genotypes cannot be manifest, therefore, by tests in a single, standard environment.

Effects of varying the dietary nitrogen to carbohydrate ratio upon the biological performance of adult Dacus oleae. (Diptera Tephritidae)

By varying the dietary proportions of nitrogen to carbohydrate in a chemically defined diet, it was found that the olive fruit adult fly cannot utilize amino nitrogen as an energy source, while the most critical ingredient for prolonged survival was the carbohydrate part of the diet. Increase of the nitrogen contents above 2.6%, up to 6.4%, shortened adult life span by 50%. The best reproduction rate was scored under a N/C ratio of 1.6/40, while higher nitrogen contents reduced egg deposition. Fertility was adversely affected by low sucrose concentrations as well as by total absence of amino nitrogen, while higher nitrogen concentrations proved also detrimental egg hatchability.