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 an
aquatic environment. To address the biomechanics of locomotion on rigid
substrates, we studied the 'somersaulting' locomotion in Hydra.
We applied atomic force microscopy to measure the local mechanical
properties of Hydra's body column and identified the existence of
differential Young's modulus between the shoulder region versus rest
of the body column at 3:1 ratio. We show that somersault primarily depends
on differential 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 variation in the body column by modulating the extracellular
matrix (ECM) polymerization impairs the 'somersault' movement.
These results provide mechanistic basis for the evolutionary significance
of differential extracellular matrix properties and tissue stiffness.