Dr. Steven Brady Professor, Southern Connecticut State University Boulevard of broken frogs: The perils of polluted ponds and life beside the road Human impacts on wild populations are numerous and extensive, degrading habitats and causing population declines across taxa. Residing perhaps in the shadows of climate change, roads and their many contaminants remain a widespread but often overlooked threat to biota, fragmenting landscapes and delivering suites of pollutants to adjacent habitats. In the snowbelt region of North America, deicing salts – used to melt snow and ice on roads and other impervious surfaces – is causing the salinization of many freshwater habitats. There, these added salts join a bevy of other runoff pollutants that threaten environmental health. Simultaneously, roads and their pollutants can act as agents of natural selection. Increasingly, it is becoming clear that road salt and other pollutants are driving population divergence across contemporary timescales. However, the capacity for local populations to adapt to these stressors remains unclear. Here, we consider the effects of road adjacency and road salt exposure on a pair of amphibian species, the spotted salamander (Ambystoma maculatum) and the wood frog (Rana sylvatica), which are found throughout much of North America. At the population level, these two species of spring-breeding amphibians exhibit contrasting responses to polluted roadside ponds. Spotted salamanders show evidence for local adaptation to roadside habitats. Wood frogs present a complex suite of maladaptive traits expressed during aquatic life stages but adaptive traits in terrestrial life stages. For instance, embryonic survival is relatively low for roadside populations yet adults from these populations have increased fecundity and locomotion. Further, recent evidence suggests that temperature has an exacerbating effect on salt toxicity, especially for roadside populations, and that a pair of genes might underlie the differential sensitivity found between populations. Together, this work indicates that exposure to pollution can have complex transgenerational effects, both adaptive and maladaptive, and that life history tradeoffs and potentially negative pleiotropy might mediate these outcomes.
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