A genomic footprint of a moving hybrid zone in marbled newts

We developed a panel of 44 nuclear genetic markers and applied this to two hybridizing species of marbled newts in the north (Triturus marmoratus) and the south (Triturus pygmaeus) of the Iberian Peninsula, to investigate pattern and process of interspecific gene flow. The northernmost occurrence of T. pygmaeus genetic material was in a T. marmoratus population north of the Vouga river estuary. This suggested the past presence of a hybrid zone, possibly coinciding with a natural river outlet at ca. 1200 A.D. Since 1808, the species contact may have moved back south to a by then completed, man‐made Vouga channel. We also found evidence for a T. marmoratus genomic footprint in T. pygmaeus from the Serra de Sintra, near Lisbon. In combination with a previously reported southern, relic occurrence of T. marmoratus in between both areas, the data point to the superseding with hybridization of T. marmoratus by T. pygmaeus. We estimate that the species hybrid zone has moved along the Atlantic coast over a distance of ca. 215 km. Two species of marbled newts in the Iberian Peninsula engage in a narrow hybrid zone. Molecular and geographical data indicate that the zone has, in recent times, moved northwards along the Atlantic coast, over a distance in excess of 200 km.