The network of roads on the landscape is vast, and has wide-reaching ecological influence. Recent investigations have focused on understanding impacts of contaminants from road runoff, especially deicing agents such as road salt. Much of our understanding of this phenomenon concerns rivers and streams. By comparison, little is known about the impacts of runoff on ephemeral wetlands. Yet, the small and shallow nature of these systems may render them highly susceptible to the influence of runoff, wherein high concentrations of contamination are possible. At present, our understanding of the impacts of roads and runoff stops at the species level. Yet, the growing body of literature reporting phenotypic and genetic differentiation among local populations prompts investigation beyond the species level. I investigated the influence of road proximity and runoff on the spotted salamander. I asked whether road proximity and runoff influence spotted salamander performance, and if so, whether this influence is dependent on population origin with respect to road adjacency. To answer these questions, I conducted field-based reciprocal transplant experiments coupled with road salt exposure experiments. For all experiments, I sourced embryos from each of five roadside and five woodland wetlands, collected within 48 hours of oviposition. Here, roadside wetlands are those located < 10 from a paved road and woodland wetlands are those located > 200 m from any road.
Results/Conclusions
Spotted salamander embryos and larvae survived less and exhibited substantially higher incidences of malformations when reared in roadside wetlands or exposed to road salt. Further, the magnitude of these responses depended on wetland origin type: Individuals originating from roadside wetlands consistently performed worse than those originating from woodland wetlands. These results indicate first that road salt and road adjacency negatively influence spotted salamander performance, and second that this influence depends on wetland origin type (i.e. roadside versus woodland). This suggests that the subset of the population of spotted salamanders most susceptible to the influence of roadside environments may be that which is least capable of persisting there. These results pose questions about the mechanisms generating this differentiated response, and indicate that roadside wetlands may induce sink dynamics coupled with inherited negative environmental effects.
