Phylogeography, hybrid zones and contemporary species boundaries in the south-eastern Australian smooth frogs (Anura: Myobatrachidae: Geocrinia)

[Display omitted] •We observed patterns of divergence, secondary contact and mitonuclear discordance in the Australian smooth frog (Geocrinia) complex consistent with contraction and expansion of species’ ranges through glacial cycles.•Our admixture analyses provide new insight into the dynamics of a comprehensively studied hybrid zone, confirming it is narrow (9–30 km wide), has remained spatiotemporally stable within an ecotone for > 50 years, and is likely influenced by female mate-choice bias.•We describe an evolutionarily distinct, range-restricted taxon endemic to the Otway Plains and Ranges, south-western Victoria, Australia. Paleo-climatic fluctuations have driven episodic changes in species distributions, providing opportunities for populations to diverge in isolation and hybridise following secondary contact. Studies of phylogeographic diversity and patterns of gene flow across hybrid zones can provide insight into contemporary species boundaries and help to inform taxonomic and conservation inferences. Here we explore geographic diversity within the acoustically divergent yet morphologically conserved south-eastern Australian smooth frog complex and assess gene flow across a narrow hybrid zone using mitochondrial nucleotide sequences and nuclear genome-wide single nucleotide polymorphisms. Our analyses reveal the presence of an evolutionarily distinct taxon restricted to the Otway Plains and Ranges, Victoria, which forms a narrow (9–30 km wide), spatiotemporally stable (>50 years) hybrid zone with Geocrinia laevis, which we describe herein as a new species.