Maintenance of Colour Polymorphism in Adder, Vipera berus, Populations: A Test of a Popular Hypothesis

• Published in: Oikos Vol. 50; no. 1; pp. 13 - 16
• Main Authors: Forsman, Anders, Ås, Stefan
• Format: Journal Article
• Language: English
• Published: Oxford Munksgaard International Booksellers and Publishers 01-09-1987; Blackwell
• Subjects: Amphibia and reptilia; Animal ethology; Animal morphology; Archipelagos; Biological and medical sciences; Body temperature; Fall lines; Food intake; Fundamental and applied biological sciences. Psychology; Linear regression; Predation; Psychology. Psychoanalysis. Psychiatry; Snakes; Vertebrata; Vipera berus; Voles; Vertebrata; Sweden; Europe; Color; Reptilia; Ophidia; Polymorphism
• ISSN: 0030-1299; 1600-0706
• DOI: 10.2307/3565396

According to a current hypothesis, the colour polymorphism in populations of the adder, Vipera berus L., is maintained by a thermal superiority of melanistic snakes, which enables them to grow more quickly than normally coloured ones. Since larger males are superior in sexual combats, and larger females get more offspring, this clearly should favour the melanistic trait. On the other hand, melanistic individuals are believed to suffer a higher predation pressure due to their more conspicuous appearance. The prediction from this hypothesis is that melanistic individuals on average should be larger than normal individuals in mixed populations. This prediction was tested on adders captured on several small islands in the Stockholm archipelago (N 59°20′; E 19°20′). No significant difference was found in weight, length or weight/length ratio between melanistic and normally coloured male adders. Neither slope nor elevation of the regression lines of length on weight differed. Thus, the hypothesis was not supported by our data.