Differential tissue stiffness of body column facilitates locomotion of Hydra on solid substrates

The bell-shaped members of Cnidaria typically move around by swimming whereas the Hydra polyp can perform locomotion on solid substrates in aquatic environment. To address the biomechanics of locomotion on rigid substrates, we studied the 9somersaulting9 locomotion in Hydra. We applied atomic force microscopy on the whole animal to measure the local mechanical properties of body column and identified the existence of differential Young9s modulus between the shoulder region versus rest of the body column at 3:1 ratio. We show that this movement depends primarily on graded variations in tissue stiffness of the body column and is explained by computational models that accurately recapitulate the mechanics involved in this process. We demonstrate that perturbation of the observed stiffness gradient in hydra body column by modulating the extracellular matrix (ECM) polymerization impairs the 9somersault9 movement. These results provide mechanistic basis for the evolutionary significance of differential ECM properties and tissue stiffness.