Abstract
While the ecological consequences of roads are well described, little is known of their role as agents of natural selection, which can shape adaptive and maladaptive responses in populations influenced by roads. This knowledge gap persists despite a growing appreciation for the influence of evolution in human-altered environments. There, insights indicate that natural selection typically results in local adaptation. Thus, populations influenced by road-induced selection should evolve fitness advantages in their local environment. Contrary to this expectation, wood frog tadpoles from roadside populations show evidence of a fitness disadvantage, consistent with local maladaptation. Specifically, in reciprocal transplants, roadside populations survive at lower rates compared to populations away from roads. A key question remaining is whether roadside environmental conditions experienced by early stage embryos induce this outcome. This represents an important missing piece in evaluating the evolutionary nature of this maladaptation pattern. Here, I address this gap using a reciprocal transplant experiment designed to test the hypothesis that embryonic exposure to roadside pond water induces a survival disadvantage. Contrary to this hypothesis, my results show that reduced survival persists when embryonic exposure is controlled. This outcome indicates that the survival disadvantage is parentally mediated, either genetically and/or through inherited environmental effects. This result suggests that roadside populations are either truly maladapted or potentially locally adapted at later life stages. I discuss these interpretations, noting that regardless of mechanism, patterns consistent with maladaptation have important implications for conservation. In light of the pervasiveness of roads, further resolution explaining maladaptive responses remains a critical challenge in conservation.
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Acknowledgements
I am grateful to the Leopold Schepp Foundation for support of this work through scholarship. I thank D Skelly, S Alonzo, P Turner, M Urban, A Hendry, J Richardson, and R Calsbeek for key guidance and project advice, and helpful conversations on the manuscript. I am grateful to S Bolden for extensive field and lab support. S Attwood, B and H Bement, E Crespi, E Hall, and J Bushey assisted in the field.
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SPB conceived, designed, and executed this study and wrote the manuscript. No other person is entitled to authorship.
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This research was supported by funding from the Mianus River Gorge Preserve Research Assistantship Program, the Hixon Center for Urban Ecology, and National Science Foundation (DEB 1011335).
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Communicated by Raoul Van Damme.
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Brady, S.P. Environmental exposure does not explain putative maladaptation in road-adjacent populations. Oecologia 184, 931–942 (2017). https://doi.org/10.1007/s00442-017-3912-6
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DOI: https://doi.org/10.1007/s00442-017-3912-6