Industrial Melanism in the Seasnake Emydocephalus annulatus

• Published in: Current biology Vol. 27; no. 16; pp. 2510 - 2513.e2
• Main Authors: Goiran, Claire, Bustamante, Paco, Shine, Richard
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 21.08.2017
• Subjects: Animals; bioaccumulation; Color; color polymorphism; Elapidae; Hydrophiidae - physiology; Hydrophiinae; industrial melanism; Laticaudinae; New Caledonia; Pigmentation; trace elements; Water Pollutants, Chemical - adverse effects; Water Pollutants, Chemical - metabolism; Water Pollution, Chemical - adverse effects; industrial melanism; trace elements; color polymorphism; Elapidae; Laticaudinae; bioaccumulation; Hydrophiinae
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2017.06.073

Although classically associated with urban environments in invertebrates, melanism in terrestrial snakes is more often linked to occupancy of cool climates [1–3]. Thermal advantages to melanism do not apply in aquatic snakes [4], but although turtle-headed seasnakes (Emydocephalus annulatus) are banded or blotched across a wide geographic range [5], most individuals are melanic in polluted inshore bays of the Pacific island of New Caledonia [4]. Why has melanism evolved in these urban sites? Because trace elements bind to melanin, darker feathers enhance a bird’s ability to shed pollutants [6]. Reptiles in polluted habitats also accumulate trace elements, which are expelled when the skin is sloughed [7–11]. Might melanism enable snakes to rid themselves of harmful pollutants? We measured trace elements in sloughed skins of seasnakes from urban-industrial versus other areas and in dark versus light skin. For the latter comparison, we used data from laticaudine seasnakes (sea kraits Laticauda spp.), in which each individual is dark and light banded, facilitating comparisons between dark and light skin. As predicted, concentrations of trace elements were higher in snakes from urban-industrial areas and higher in darker than paler skin (even within the same slough). The rate of excretion of trace elements is further enhanced by higher frequencies of sloughing in melanic than banded individuals, even within the same population, because of higher rates of algal settlement on darker skin. Thus, melanism of seasnakes in polluted sites may facilitate excretion of trace elements via sloughing. [Display omitted] •Turtle-headed seasnakes are melanic (black) in polluted sites, but not in other areas•Melanin binds trace elements that are excreted when the snake sloughs•Trace-element concentrations are higher in polluted sites and in darker skin•Melanism in seasnakes from urban sites may facilitate excretion of pollutants Goiran et al. found that within a wide-ranging seasnake species, melanism (black color) was common only in polluted sites. Darker skin enables snakes to excrete trace-element pollutants by binding pollutants to melanin in the shed skin and by inducing more frequent sloughing.