Roads impose a diverse suite of negative effects on wild populations. Pollution, road-kill, and habitat fragmentation are just a few of the common stressors found across modern landscapes traversed by roads. Owing to the pervasiveness of the global road network, these impacts are widespread, and extend well beyond the footprint of the road surface itself. For instance, an estimated 20% of the landscape in the U.S. is ecologically affected by roads. While these ecological consequences of roads are well described, evolutionary consequences remain poorly understood. Yet owing to intraspecific variation, road effects are not universally detrimental to all individuals in a population, and indeed can act as agents of natural selection. The nature of this selection and the response to it will ultimately influence the long-term persistence of populations exposed to road effects. Thus, developing evolutionary-based insights will be crucial to understanding the full impact of roads on natural populations.
Our previous work has shown that evolutionary responses to roads and runoff pollution differ among species, even among co-habiting, related species breeding and dwelling in the same wetlands. For instance, roadside populations of a salamander are locally adapted to roads and road salt pollution. These populations achieve higher fitness in roadside wetlands compared to populations experimentally transplanted there from unpolluted wetlands away from roads. Similar manipulations with a species of frog reveal the exact opposite effect: roadside frog populations achieve lower fitness in their home wetlands compared to frogs transplanted there from unpolluted sites. This pattern of ‘local maladaptation’ is surprising given that adaptive variation is present in nearby populations located away from roads. Several processes can contribute to this maladaptive outcome, including contaminant transfer from parent to offspring, maladaptive evolution, DNA damage, and biased gene flow patterns.
Motivated by these divergent outcomes among species, our work is aimed at understanding the full nature of environmental change in habitats affected by roads. We are guided by the overarching goal of developing predictive understanding of population level responses to roads and runoff pollution. Toward that goal, we work across biological scales (from molecular to community level) to identify differential fitness patterns across populations and investigate potential mechanisms underlying such differences. In complement, we are interested in characterizing the suite of contaminants found in roadside wetlands (e.g. road salts, heavy metals, PAHs). We are particularly interested in describing spatio-temporal variation of these contaminants across landscapes and assessing the accumulation and transgenerational movement of contaminants in amphibians relying on roadside wetlands. In the future, we plan to investigate additional stressors related to climate change and disease dynamics to more fully understand the impacts of environmental change on roadside habitats.