Sea snakes

This is intriguing. Sea snakes are descended from venomous land-dwellers that reentered the oceans some 5 million years ago. While the terrestrial descendant of those snakes show a wide range of color patterns, sea snakes are pretty consistently banded. Why?

That's the question investigated by a group from the University of Sydney published recently in Proceedings of the Royal Society B. The researchers felt that sea snakes provide an excellent opportunity to investigate the evolutionary pressures of life in the sea as it compares to a terrestrial existence. We know that selection gave sea snakes a paddle-like tail and large lungs, but what about those bands?

Looks like it might be related to algal fouling. Fouling has been reported in some sea snakes, and has serious impacts on hydrodynamics when it occurs. To examine the potential effect of coloration on fouling, the research team utilized a population that exhibits exhibits considerable variation, with individuals ranging from a uniform black to a distinctive banding pattern. Over a four year period, the research team found that black individuals sported significantly more algae than the banded individuals. To ensure that it was actually coloration that was driving the difference, the team went the extra mile. They suspended plastic models of snakes in three different color morphs, black, while, and black/white, and followed the fouling process. Sure enough, the black models supported the highest algal density, with black-and-white, and white models trailing behind. This is apparently related to the fact that some algal spores actually settle out preferentially on darker substrates.

Of course, the question arises. Why are there black sea snakes? Why aren't they all white? The answer, no doubt, lies in that most universal of all evolutionary phenomena - trade-offs. No matter how many factors you've thought of, there's always one you haven't.