Landscape genetics reveals the role of watercourses in driving gene flow in Chioglossa lusitanica

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Riparian ecosystems are increasingly affected by anthropogenic pressures, resulting in habitat alteration and reduced landscape connectivity. Riparian amphibians are particularly vulnerable due to their dependence on both aquatic and terrestrial environments. Here, we investigate how landscape features are associated with patterns of genetic connectivity in Chioglossa lusitanica, an endemic stream salamander of the western Iberian Peninsula, using a high-resolution watershed-scale landscape genetic approach across the Ceira River basin. Using microsatellite data from 248 individuals sampled at 88 sites, we evaluated isolation-by-distance and isolation-by-resistance models incorporating environmental (climate and primary productivity), geographical (proximity to watercourses), and topographic variables (elevation). Genetic analyses identified two main genetic clusters, with extensive admixture in the Lousã Mountains, highlighting fine-scale genetic structuring within a single drainage system. Patterns of genetic differentiation were strongly associated with river networks, suggesting that watercourses are correlated with higher landscape permeability for gene flow at the watershed scale. Elevated allelic diversity observed at upstream and downstream extremes may indicate heterogeneity in demographic history within the watershed. No pronounced genetic discontinuities were detected between previously described subspecific groups, although lowland areas were associated with increased landscape resistance, consistent with reduced habitat suitability in human-modified landscapes. By integrating dense spatial sampling with landscape resistance modelling, our results highlight the importance of riparian landscapes in maintaining genetic connectivity in C. lusitanica. Conservation strategies should prioritize the maintenance and restoration of riparian corridors, particularly in mountainous regions, to support population connectivity in this and other riparian-dependent species.