Italian subspecies of the asp viper, Vipera aspis: Patterns of variability and distribution

The asp viper, Vipera aspis, is distributed in western Europe and comprises several morphological subspecies other than the nominal form, V. a. aspis of northern to southern France: V. a. zinnikeri, V. a. atra, V. a. francisciredi, V. a. hugyi. Each form is very often distinguishable, both by dorsal colour pattern and number of ventral scales. Examining a balanced sample for each subspecies and each sex from Italy and other areas, we found that the distributive patterns of Italian populations are as follows: V. a. atra is widely distributed throughout northwestern Italy, reaching the Ligurian Sea coasts; it passes westwards into France up to most of the Haute Provence region, turning northwards up to the Savoie region. Instead, V. a. francisciredi extends eastwards throughout the Po plain and southwards to southern Italy. The distribution limit of V. a. hugyi extends from northern Apulia southwards to the Irpini mountains, and the slopes of Mt. Vesuvius volcano, and the remaining part of Italy and Sicily. Most of the known morphological differences between aspis and francisciredi do not seem to be consistent. The subspecies montecristi is identical to hugyi. Some hypotheses of possible causes of different distributive patterns are presented.