Insect exoskeletons react to hypergravity

A typical feature of biological materials is their ability to adapt to mechanical load. However, it is not known whether the cuticle exoskeleton, one of the most common biological structures, also shares this trait. Here, we show direct experimental evidence that prolonged exposure to hypergravity conditions affects the morphology and biomechanics of an insect exoskeleton. Locusts were raised for several weeks in a custom-designed centrifuge at various levels of hypergravity. Biomechanical measurements and X-ray microtomography show that up to 3 g load Young's modulus of the tibiae increased by about 67%. Higher gravitational loads however decreased the survival rate, body mass and endocuticle thickness. These results directly show that cuticle exoskeletons can react to hypergravity. This ability has so far only been known for bone endoskeletons and plants. Our findings thus add important context to the discussion on general ultimate factors in the evolution of adaptive biological materials and skeletal systems.