Thursday, November 06, 2008

Sea Snakes Only Drink Fresh Water

Sea snakes may slither in saltwater, but they sip the sweet stuff.

So concludes a University of Florida zoologist in a paper appearing this month in the online edition of the November/December issue of the journal Physiological and Biochemical Zoology.

Harvey Lillywhite says it has been the "long-standing dogma" that the roughly 60 species of venomous sea snakes worldwide satisfy their drinking needs by drinking seawater, with internal salt glands filtering and excreting the salt. Experiments with three species of captive sea kraits captured near Taiwan, however, found that the snakes refused to drink saltwater even if thirsty — and then would drink only freshwater or heavily diluted saltwater.

"Our experiments demonstrate they actually dehydrate in sea water, and they'll only drink freshwater, or highly diluted brackish water with small concentrations of saltwater — 10 to 20 percent," Lilywhite said.

Harold Heatwole, a professor of zoology at North Carolina State University and expert on sea snakes, termed Lillywhite's conclusion "a very significant finding."

"This result probably holds the key to understanding the geographic distribution of sea snakes," Heatwole said.

The research may help explain why sea snakes tend to have patchy distributions and are most common in regions with abundant rainfall, Lillywhite said. Because global climate change tends to accentuate droughts in tropical regions, the findings also suggest that at least some species of sea snakes could be threatened now or in the future, he added.

"There may be places where sea snakes are barely getting enough water now," he said. "If the rainfall is reduced just a bit, they'll either die out or have to move."

This is something to be considered for the extinct diapsid lineages. They may not have been able to get water from the sea...somehow I doubt it for the ichthyosaurs, but you never know. Have any ever been found in deep river deposits? What about mosasaurs and the others?


Neil said...

Hmmm... I'll have to read that paper but it's worth noting that Laticauda is the least adapted sea snake and the sea kraits have likely adopted their ocean-going lifestyle independently from "true" sea snakes. Without knowing much about sea snake physiology I'm guessing that more pelagic forms, like Pelamis which has been known to cross the Pacific, are perfectly capable of drinking salt water as are other living marine diapsids (e.g. sea birds, turtles and marine iguanas). I'm also fairly confident that the vast majority of mesozoic marine reptiles drank sea water, and some (e.g. metriorynchids) even possess skeletal features that have been interpreted as housing salt excretion organs.

I'll bet that Mesozoic marine reptiles did venture into rivers on occasion, as due living marine mammals. The placodont Henodus is known from fresh water facies, but that's the only fossil example that comes to mind.

Neil said...

After a little digging I've tracked down several reports of plesiosaur remains in fluvial deposits, generally isolated teeth or bones from juveniles. So there may be an interesting life history pattern going on.

Also of interest is that most cases seem to be from high latitudes...not sure of the significance of that if there is any. I'd be happy to pass along the refs if you are interested

Will Baird said...

Yes, please!

It would be rather interesting to see if there was some sort of pattern for different aquatic paleodiapsids' life cycles.

an zha lyu -a-t- gmail doot commie