The common ground in landscape effects on gene flow in two newt species in an agroecosystem

Maintaining habitat connectivity is crucial for maintaining genetic diversity and reducing the risk of inbreeding depression in numerous species. Human-modified habitats pose a threat to population persistence, particularly for amphibians that require both aquatic and terrestrial habitats and often exhibit low dispersal capacity. In this study, we investigated the genetic structure and variation of two sympatric newt species, Triturus cristatus and Lissotriton vulgaris, in an urbanized and agricultural landscape. Using a multiscale resistance modeling approach, we evaluated how landscape features affect gene flow in both species. Our results confirmed that the less abundant T. cristatus exhibited more genetically distinct demes than the more common L. vulgaris, which showed a more subtle structure. Additionally, levels of genetic variation were lower in T. cristatus than in L. vulgaris, but with a similar spatial distribution pattern across shared ponds. We found that the proportion of managed grassland in the study area played a major role in reducing the level of connectivity in both species. Furthermore, considering multiple spatial scales proved to be effective in improving the fit of the landscape resistance models, with the largest scale (900 m) providing the best fit. In T. cristatus, areas with low proportions of trees or high proportions of crop fields negatively affected genetic connectivity. Notably, resistance surfaces optimized for each species were highly correlated. The intensively managed grassland lacked the structural heterogeneity necessary for newts. Therefore, switching to a more traditional management approach in the landscape to increase spatial patchiness at the scale of dispersal would benefit both species.