Cryptic phylogeographic diversifications provide unique models to examine the role of phylogenetic divergence on the evolution of reproductive isolation, without extrinsic factors such as ecological and behavioural differentiation. Yet, to date very few comparative studies have been attempted within such radiations. Here, we characterize a new speciation continuum in a group of widespread Eurasian amphibians, the Pelobates spadefoot toads, by conducting multilocus (restriction site associated DNA sequencing and mitochondrial DNA) phylogenetic, phylogeographic and hybrid zone analyses. Within the P. syriacus complex, we discovered species‐level cryptic divergences (>5 million years ago [My]) between populations distributed in the Near‐East (hereafter P. syriacus sensu stricto [s.s.]) and southeastern Europe (hereafter P. balcanicus), each featuring deep intraspecific lineages. Altogether, we could scale hybridizability to divergence time along six different stages, spanning from sympatry without gene flow (P. fuscus and P. balcanicus, >10 My), parapatry with highly restricted hybridization (P. balcanicus and P. syriacus s.s., >5 My), narrow hybrid zones (~15 km) consistent with partial reproductive isolation (P. fuscus and P. vespertinus, ~3 My), to extensive admixture between Pleistocene and refugial lineages (≤2 My). This full spectrum empirically supports a gradual build up of reproductive barriers through time, reversible up until a threshold that we estimate at ~3 My. Hence, cryptic phylogeographic lineages may fade away or become reproductively isolated species simply depending on the time they persist in allopatry, and without definite ecomorphological divergence.

Vipera ursinii graeca is a restricted-range, endemic snake of the Pindos mountain range in the southwestern Balkans. The subspecies was previously reported from eight localities in Greece and one locality in southern Albania. We used species distribution modelling based on climate data from known localities in Greece to estimate the potential distribution of the subspecies. The model predicted suitable areas for eleven mountains in southern Albania, which we visited in ten field expeditions in four years. Based on 78 live individuals and 33 shed skins, we validated the presence of the snake on eight of the eleven mountains. Six populations (Dhëmbel, Llofiz, Griba, Shendelli, Tomorr and Trebeshinë Mountains) are reported here for the first time. Morphological characters undoubtedly supported that all individuals found at these new localities belong to V. u. graeca. Genetic analysis of mitochondrial DNA sequences also confirmed the identity of the snakes as V. u. graeca and a low number of identified haplotypes suggested low genetic variability among populations despite significant spatial isolation. All localities were subalpine-alpine calcareous meadows above 1600 m. These high montane habitats are separated by deep valleys and are threatened by overgrazing, soil erosion, and a potential increase in the elevation of the tree line due to climate change. Our surveys increased the number of known populations by 60% and the known geographical range of the subspecies by approximately 30%. Our study serves as a baseline for further ecological research and for conservation measures for one of the least known European viperid snakes.