Integrative taxonomy reveals two species and intraspecific differentiation in the Vipera latastei–monticola complex

Modern taxonomy relies on the unified species concept and integrative approaches to delimit evolutionary coherent taxa. The western Mediterranean vipers within the Vipera latastei–monticola complex (Vipera latastei and Vipera monticola) have a rather old taxonomic history marked by the prevalence of morphological criteria in the recognition of taxonomic units. Recent phylogenetic inferences, however, contradict this taxonomic scenario, highlighting the need of integrative studies to properly evaluate the taxonomy of this complex. Here, we apply an integrative taxonomic approach, combining phylogeographic, morphological, and ecological analyses, to identify and describe evolutionary coherent taxonomic units within the Vipera latastei–monticola complex. Using dated mtDNA phylogenetic relationships, we spatially delimit two levels of evolutionary units, which are the subject of morphological and ecological comparisons. The first level corresponds to two Miocene vicariant clades, with considerable morphological distinctiveness that we identified as different species: V. latastei in the Iberian Peninsula, and V. monticola in North Africa. The second level corresponds to three Pliocene parapatric lineages within each of these species, which we recognized with subspecific status due to non-apparent geographic isolation and variable levels of phenotypic distinctiveness. Consequently, we propose distributional rearrangements in the previously recognized taxa, as well as define three new subspecies: Vipera latastei arundana ssp. nov. in southern Iberia, Vipera monticola atlantica ssp. nov. in the western High Atlas Mountains and Vipera monticola saintgironsi ssp. nov. in the eastern High Atlas, Middle Atlas, Rif, Tellian Atlas and Aurès Mountains. Our proposed taxonomic scenario anticipates important outcomes for the conservation status of these Mediterranean taxa.