Human-induced habitat loss and deterioration are shaping connectivity patterns of numerous taxa around the globe. When natural levels of connectivity are disrupted, many potentially synergistic factors (e.g., demographic, genetic and environmental) can jeopardize the future of taxa (Crooks & Sanjayan, 2006;Richardson et al., 2016). In the short-term, isolated populations become more prone to extirpations through random demographic or environmental events as well as the deleterious genetic consequences of increased inbreeding (Bell et al., 2019;Frankham et al., 2002). In the long-term, reduced connectivity decreases the opportunity for

The riverine barrier hypothesis (RBH) posits that rivers comprise geographical barriers to gene ow for terrestrial organisms, thus promoting genetic differentiation between populations. Here, we explored the RBH on larviparous and pueriparous populations of the live-bearing re salamander (Salamandra salamandra). While larviparous re salamanders exhibit a semi-aquatic life cycle (females deposit pre-metamorphic larvae on water), pueriparous salamanders present a fully terrestrial life cycle (females deliver terrestrial juveniles) and, therefore, a greater independence from water for survival and reproduction. We performed a ne-scale sampling of opposite transects in 11 rivers (six and ve for larviparous and pueriparous populations, respectively) to test the hypothesis that rivers are more effective barriers for pueriparous salamanders due to their fully terrestrial life cycle. We carried out individual-and population-based genetic analyses using 14 microsatellites and a mitochondrial marker to examine the extent to which rivers hinder short-and long-term gene ow. We found that rivers are semi-permeable obstacles for both larviparous and pueriparous populations, although they appear to be more effective barriers for the latter when rivers with similar attributes are compared. We also found that river width and possibly the presence of crossing structures may in uence the genetic barrier effects of rivers in re salamanders. This is one of the very few studies in amphibians showing how different reproductive strategies in uence the barrier effects imposed by rivers.

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.