Cryptic diversity among Western Palearctic tree frogs: Postglacial range expansion, range limits, and secondary contacts of three European tree frog lineages (Hyla arborea group)

► Uncovering cryptic biodiversity of threatened European amphibians (Hyla arborea group). ► Divergence times, diversity, distributions for three recently recognized tree frog lineages. ► Range borders, secondary contact zones, signatures of a postglacial range expansion. ► Data support conservation by fine-tuning measures to lineage-specific Quaternary refugia. ► Suture zones as natural arenas to generate biodiversity and study speciation.