VARIATION IN NUMBER OF VENTRAL SCALES IN SNAKES - EFFECTS ON BODY SIZE, GROWTH-RATE AND SURVIVAL IN THE ADDER, VIPERA-BERUS

The relationship between number of ventral scales, correlating with nu mber of body vertebrae, and body size of adders, Vipera berus, was inv estigated using captive-born young and wild-caught adults (snout-vent length > 400 mm) from six populations in eastern Sweden. Females had s ignificantly more ventral scales, and were larger, than males in all p opulations. Among adult individuals, snout-vent length was highly posi tively correlated with the number of ventral scales when differences d ue to sex and locality were controlled for. The same pattern was true for newborn individuals when differences due to litter and sex were co ntrolled for. The influence of number of ventral scales on survival an d growth rate as possible causes of this positive correlation was exam ined. Mean number of ventral scales was lower in new-born snakes than in adults, indicating selection against individuals with a low scale c ount. Since this selection appears to take place in the early juvenile phase, it is inadequate to explain the relationship between adult bod y size and number of ventral scales. However, individuals with many ve ntral scales had significantly higher growth rates than individuals wi th few ventrals. This suggests that individuals with many ventral scal es enjoy a higher growth rate and therefore are able to reach a larger size than their conspecifics of the same age with few ventral scales. This would explain the positive relationship between body size and ve ntral scale number observed in new-born and adult snakes.