Barred, blotched or intermediate? A photographic-based survey on the spatial distribution of Vipera aspis phenotypes from central-southern Italy

Abstract

Variation in animal colouration, which holds ecological and evolutionary significance, is evident in snakes, including the polytypic and highly polymorphic asp viper Vipera aspis. This species, currently acknowledged with four subspecies, features three of them (V. a. aspis, V. a. francisciredi and V. a. hugyi) within the Italian territory, each displaying distinct dorsal patterns. Analysing 143 georeferenced photos from personal surveys and citizen science, the present study explores transition areas between V. a. francisciredi and V. a. hugyi, revealing the coexistence of three dorsal pattern phenotypes (i.e. francisciredi, hugyi, and intermediate) across central-southern Italy. The outcome of the work reveals occurrences of francisciredi phenotypes considerably beyond the southern limit indicated in recent literature. Remarkably, intermediate phenotypes cover a significant portion of southern Italy, including Apulia (three records), Basilicata (six records) and Campania (three records) regions, and overlapping with both hugyi and francisciredi ranges. These findings suggest asymmetrical gene flow from northern to southern populations, resembling patterns observed in other reptiles. The intricate distribution of colour phenotypes underscores the necessity for molecular investigations to comprehend the genetic context and evolutionary history of V. aspis populations from central-southern Italy.