How urban seasnakes lost their stripes
WATCH: Seasnakes are turning black because of pollution, a study in New Caledonia has shown, while the snakes in pristine waters retain their stripes. Corresponding author Professor Rick Shine explains the phenomenon in a video.
Even on a 'pristine' coral reef, human activities can pose very real problems.
Snakes shed their stripes to survive
Turtle-headed seasnake photos by Claire Goiran. Video by Terri Shine.
Researchers studying turtle-headed seasnakes living on coral reefs in the Indo-Pacific noticed something unusual about the snakes鈥� color patterns: seasnakes living in more pristine parts of the reef were decorated with black-and-white bands or blotches. Those in places with more human activity鈥攏ear the city or military activity鈥攚ere black.
As reported in Current Biology聽today, those color differences are explained by differences in the snakes鈥� exposure to pollution. The blacker skin of urban seasnakes allows the animals to more effectively bind and rid their bodies of contaminants, including arsenic and zinc, each time they shed their skins. The findings add seasnakes to a growing list of species that show industrial melanism, a greater prevalence of dark-colored varieties in industrial areas.
鈥淭he animals I study continue to astonish me,鈥� said at the University of Sydney's 聽in the Faculty of Science.
鈥淚 think it鈥檚 remarkable to find industrial melanism in organisms as different as moths and seasnakes!鈥�
Claire Goiran, the study鈥檚 lead author, at Labex Corail & Universit茅 de la Nouvelle-Cal茅donie got the idea that blacker skin might be related to pollutant exposure after learning that the darker feathers of urban pigeons in Paris store more zinc than lighter feathers. Goiran and her colleagues wondered whether a similar thing might be happening in the seasnakes.
To find out, the researchers measured trace elements in the sloughed skins of seasnakes from urban-industrial versus other areas and in dark versus light skin. As predicted, they report, concentrations of trace elements were higher in snakes from urban-industrial areas. Trace element concentrations were also higher in darker than in paler skin.
The researchers further found that darker snakes slough their skins more often. As a result, it appears that seasnakes whose skin is more heavily pigmented with melanin have an advantage over their lighter relatives in polluted areas.
Professor Shine says that the findings are yet another example of rapid adaptive evolutionary change in action. For him, it鈥檚 also a more sinister reminder that 鈥渆ven on an apparently pristine coral reef, human activities can pose very real problems for the animals that live there鈥�.