Do Scale Anomalies Cause Differential Survival in Vipera berus?

• Many snake populations contain moderate to high frequencies of individuals with ventral scale anomalies, which are often associated with duplicated or fused vertebrae and ribs and are known to impair locomotion and growth. In an attempt to test whether such anomalies may influence survival, we examined their frequency among cage-reared juvenile adders, Vipera berus, and wild-caught individuals that presumably had been exposed to natural selection. Midbody ventral scale anomalies were significantlyless frequent among snakes exposed to selection than among cage-reared juveniles in one of three populations studied, indicating that they might indeed reduce survival. Furthermorem, idbody anomalies wereless common among large than among small wild-caught individuals, although not significantly so. The association between anomalies among captive mothers and their offspring was very weak, indicating low heritability of this trait. This low heritability might explain why scale anomalies are common in adder populations in spite of the apparent selection against anomalous individuals. We also found the proportion of anomalous offspring to increase with litter size, suggesting a trade-off between number and quality of young.

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