Melanism is the unusual darkening of the body tissues caused by excessive production of melanin (a dark pigment in the skin), especially as a form of colour variation in animals. And it has been discovered that pollution from mining activities encourage some sea snakes to evolve black skins.
This may be the first evidence of industrial melanism in a marine species.
It has long been observed that there exists the industrial melanism in invertebrate species -- the most renowned being the peppered moth. The frequency of dark-coloured moths skyrocketed during England's Industrial Revolution. We have all been taught that such creatures blend in well with the bark of trees in industrial locations, therefore increasing their odds of survival and reproduction (although this might very well be an oversimplification).
Rick Shine at the University of Sydney and his colleagues' study about the Indo-Pacific snakes provide a good example of the ceasing rarity of industrial melanism in vertebrates.
Emydocephalus annulatus, also known as the turtle-headed sea snake, is generally found in particular tropical oceans near Australia. The snakes usually look a lot like monochromatic banded candy canes. However, in a nearby barrier reef in the polluted areas on the French island territory of New Caledonia, north-east of Brisbane, were snakes totally enveloped in black skin. Shine and his colleagues already knew that pollutants such as arsenic or lead can truss to melanin, so they speculated whether this might explain the colour of the found snakes.
To find out, the group made time to collect and analyze the skins naturally shed by these creatures in industrial and non-industrial waters. The sea snakes characteristically shed or slough their skin a few times a year.
Shine and his colleagues found that the concentrations of 13 trace elements among the 17 sloughs (cobalt, manganese, lead, zinc, and nickel, respectively) were higher in the snakes habituating near urban areas, and higher in darker skin. He reports that similar concentrations of the elements cause extreme health issues in numerous domesticated species -- from cattle to poultry.
Furthermore, the study found that the darker sea snakes slough their skins twice as often as the lighter ones, suggesting that the former are undoubtedly adapting to handle the pollution in the water they inhabit -- developing their skins with better capacity to marsh potentially harmful trace elements and sloughing skin more often than usual to reduce the element load they ought to deal with.
This study should be a wake-up call about the high risks of polluting ocean environments according to Shine. "Our research suggests that the snakes are rapidly evolving to help them deal with these new challenges, but there are limits to that resilience. We need to stop treating the ocean as a toilet," he says.
Let's not wait for the days to be as dark then, shall we?
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