Stage-specific sensitivity and the attribution of altered-gravity responses in Drosophila melanogaster: a critical appraisal of spaceflight and ground-based platforms

Drosophila melanogaster has flown on rockets and spacecraft since 1947 and is one of the most widely used animals in gravitational biology, owing to its short life cycle, genetic tractability, modest hardware requirements and ability to develop and reproduce in orbit. Several recent reviews have catalogued its responses to spaceflight and altered gravity. This Mini Review addresses two questions. First, does sensitivity to altered gravity differ across developmental stages once differences in study design are taken into account? Second, how confidently can responses observed on ground-based platforms be attributed to altered gravity rather than to platform-specific physical or environmental factors? The available evidence identifies oogenesis, embryogenesis and metamorphosis as candidate gravity-sensitive windows, but studies of different stages have used different strains, hardware, exposure durations, gravity levels, controls and endpoints, so the data do not yet support a ranking of stages by sensitivity. Adult responses in immunity, cardiac function, the nervous system and behavior are documented in spaceflight, and in-flight 1 g centrifuge controls show that only part of them can be attributed to reduced gravity. Each ground-based platform introduces characteristic confounders, including fluid motion and limited gas exchange on rotating devices, strong magnetic fields in diamagnetic levitation and Coriolis forces in centrifuges. We summarize, for each platform, the applicable sample scale, main confounders and required controls. Finally, we discuss acoustic levitation, a contact-free technique that does not reproduce free fall and propose the validation steps it would require before use as an altered-gravity platform.