The move from life on land to life in the sea has led to the evolution of a new sense for sea snakes, potentially making them more likely to be able to sense vibrations from all directions, an Australian study suggests.
The international team studied tiny and poorly understood structures on the heads of snakes called 'scale sensilla'.
"Land snakes and many lizards have small raised structures on the scales on their heads -- called scale sensilla -- that they use to sense objects by direct touch," said lead author Jenna Crowe-Riddell from the University of Adelaide in Australia.
"We found that the scale sensilla of sea snakes were much more dome-shaped than the sensilla of land snakes, with the organs protruded further from the animals' scales, potentially making them more likely to be able to sense vibrations from all directions," Crowe-Riddell noted.
The researchers also found that scale sensilla on some of the fully aquatic snakes covered a much higher proportion of the scales' surface.
"We believe sea snakes use these organs to sense objects at a distance by 'feeling' movements in the water. This hydrodynamic sense is not an option for land animals. In water, a new way of sensing the environment becomes possible," Crowe-Riddell noted.
The researchers looked at 19 species of snakes, including fully-aquatic, semi-aquatic and land species, and measured the coverage of sensilla over single scales on their heads.
They used DNA sequencing to reconstruct the evolutionary relationships between the snakes, and used microscope imaging and specially developed software to automatically detect the small organs from silicone casts of snake heads. They also examined the shape of the sensilla using scanning electron microscopy.
The research was published in the Royal Society journal Open Biology.