Captive breeding unveils hybridisation between aquatic and terrestrial reproductive modes and a reversal reproductive shift within Salamandra salamandra gallaica

Bimodal reproductive species offer an excellent opportunity to study the evolution of reproductive shifts, yet are extremely rare among vertebrates. Salamandra salamandra is one of two bimodal amphibian species, showing two viviparity modes: an aquatic (larviparity) and a terrestrial (pueriparity) mode. Although hybridization between larviparous and pueriparous lineages occurs in natural contact zones, their reproductive output is unknown. We conducted a captive breeding experiment to cross pueriparous insular females and larviparous continental males of S. s. gallaica. We first confirmed the reproductive output of the females and used parentage analysis to confirm the parents of the offspring, which resulted in a single group of aquatic larvae. We report, for the first time, direct evidence of F1 hybrids between parity modes in urodeles and a case of parity mode reversal at the individual level. Our study highlights S. salamandra as a bimodal reproductive species that offers exceptional opportunities to understand the evolution of viviparity.