HEATING RATES AND BODY-TEMPERATURE VARIATION IN MELANISTIC AND ZIGZAGVIPERA-BERUS - DOES COLOR MAKE A DIFFERENCE

Reptiles rely upon external heat sources to increase body temperature, and it has been suggested that thermoregulatory capacity may vary amo ng individuals of different colour morphs because colours differ in re flectance and may influence the rate at which solar radiation is conve rted into body heat. Individuals with superior thermoregulatory abilit ies may either maintain higher body temperatures, and thereby enjoy in creased performance, or they may decrease time spent basking, and ther eby reduce the potential costs, e.g. predation, associated with thermo regulation. In a comparison of thermoregulatory capacity, daily body t emperature, and proportion of time exposed between melanistic and zigz ag individuals in a population of Vipera berus polymorphic for colour pattern, melanistic individuals were found to heat faster and to reach slightly higher body temperatures than did zigzag individuals when ex perimentally exposed to identical environmental conditions. However, t here was no consistent difference in daily body temperature variation or in exposure between radiotelemetered free ranging melanistic and zi gzag individuals, despite the fact that snake body temperatures appear ed to be constrained by the physical environment for most of the study period. Either colour exerts only a trivial effect on the body temper atures of adders or melanistic individuals use their thermoregulatory advantage differently depending on gender and reproductive condition.