Serpent Research: Dehydration and drinking in sea snakes

A new article (Lillywhite et al. 2015) in the Journal of Zoology reports on the drinking behavior a sea snakes. It had been assumed sea snakes had a salt gland located under their tongue and that it was involved in the regulation of sodium ions,allowing the snakes to drink sea water. However, experimental work suggested that sea snakes, while in sea water do not drink. Instead, marine snakes dehydrate at sea and are dependent on environmental sources of fresh water to maintain water balance. They may drink freshwater off the surface of the ocean that comes from rain, or from the mouths of rivers (freshwater being less dense that salt water tends to stay on top until it is mixed with sea water; but only if it is available. Lillywhite et al (2015) investigated the dehydration and drinking responses of five species of hydrophiin sea snakes collected during the dry season in northern Australia. None of these snakes would drink sea water, even when dehydrated. Dehydrated individuals of Hydrophis curtus, H. elegans and H. zweifeli drank fresh water, and the mean threshold levels of dehydration that first elicited drinking were deficits of −26, −29 and −27% of body mass, respectively. Individuals of Aipysurus mosaicus and H. peronii did not drink fresh water when similarly dehydrated. Few snakes they collected following more than four months of drought drank fresh water immediately after capture. Species of Hydrophiin appear to have a high resistance to dehydration, which they evidently tolerate in marine habitats for extended periods during drought. Thirst in these species is significantly less sensitive than in other species, suggesting that marine snakes have variable requirements for drinking fresh water. The results illustrate that sea snakes are characterized by diverse responses to dehydration and likely have different osmoregulatory strategies for survival, with implications for better understanding the evolutionary success of secondarily marine vertebrates and their potential responses to future changes in tropical precipitation.