Mechanoreception in Hydrophis sea snakes: Drivers of ecological adaptation

Hydrophis sea snakes, like most squamate reptiles, possess small protruding mechanoreceptors on their head called scale sensilla whose function is to detect both tactile and hydrodynamic stimuli. Light and scanning electron microscopy have revealed that in Hydrophis major there are two sensilla types, called “smooth dome” and “mountains”. The former is rounded, the latter is taller and thorn-shaped. Sensilla traits were investigated using 3D imaging followed by a principal component analysis in order to identify ecological clusters for 12 species of sea snake. Sensilla height allowed to classify the study species into three groups characterised by their feeding ecology: open water specialist on spiny prey, benthic ambush predators on elongate prey and open water generalists. To resolve the question whether mechanoreception is a primary sense in Hydrophis sea snakes, the trigeminal nerve, which is the main mediator of mechanoreceptive information to the brain, was studied. Light and electron microscopy have revealed that axon count, axon caliber and myelin sheath thickness place H. major on equal footing with terrestrial tactile specialists, but below the level of specialisation of other aquatic tactile specialists.