Does the head and hemipenial morphology support the taxonomic status of the Walser’s viper (Vipera walser)?

Vipera walser has been recently elevated to the species rank on molecular bases but did not receive unanimous support. In this study we used Geometric Morphometry on three Vipera species (V. walser, V. berus, V. aspis) to investigate the variation between species and sexes in the shape of the head and to investigate whether morphology can be used to confirm the validity of V. walser as a new species. Additionally, we compared hemipenial morphology to test for reproductive barriers among species. The analyses did not show any statistically significant difference in head shape among species; however, a sexually dimorphic pattern was detected so that males tend to have longer heads along the antero-posterior axis with a narrower posterior portion compared to females. Eventually, no macroscopic difference in hemipenial morphology and ornamentations was found. Based on this evidence, we suggest a conservative approach concerning the species status of V. walser. Hence, in depth molecular analyses at the genomic level are crucial to clarify the evolutionary history of V. walser and its phylogenetic relationships with other Vipera species.