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.