All at sea: aquatic life modifies mate-recognition modalities in sea snakes (Emydocephalus annulatus, Hydrophiidae)

Alternative sensory modalities (e.g. vision, chemoreception) differ in the spatial scale, permanence and reliability of cues they provide to mate-searching males. Males of terrestrial snake species use chemoreception to locate females over large distances, but phylogenetic shifts to aquatic life render such cues unavailable. Do male sea snakes use alternative modalities for identifying potential sexual partners and if so, are the novel systems as effective for mate-finding as the ancestral ones? Observations and experiments show that free-ranging male turtle-headed sea snakes (Emydocephalus annulatus) in shallow-water reef habitats in New Caledonia use visual cues (including size, movement and color pattern) to assess whether snake-shaped objects are potential sexual partners. Skin lipids (pheromones) are important only after the male comes into physical contact with the stimulus. Visual cues provide unreliable information about potential mates, and function over short distances only (generally, <1 m). In consequence, mate-searching male snakes frequently failed to find nearby females, rarely managed to maintain contact with females they did find, and wasted time and energy investigating inappropriate stimuli (e.g. fishes, sea cucumbers, divers). The loss of effective pheromonal mate-location systems means that mate recognition by aquatic snakes functions over smaller distances than in their terrestrial relatives. Phylogenetic transitions among habitat types thus may directly modify central features of the mating system.