Impact of Freshwater Salinizaition on Wood Frog sperm Performance

Freshwater salinization poses threats to many aquatic ecosystems, particularly those polluted by salt from deicing practices in the North American snowbelt region. Much attention has focused on salinization of rivers and lakes, but less has been given to smaller water bodies such as vernal pools, which are critical for a suite of species found nowhere else. Because such pools are relatively small in volume, these habitats can reach high salinity, especially when situated besides roads or in developed landscapes. Beyond immediate ecological consequences, deicing salt can also act as an agent of natural selection, driving population divergence across gradients of salinization. Theory predicts that local populations with a lineage of exposure to elevated salinity should evolve higher tolerance over time. Indeed, experimental reciprocal transplant experiments have found that road adjacent populations of one amphibian, the spotted salamander, appear to have evolved increased tolerance to high-salinity roadside ponds. Curiously, co-habiting populations of a different amphibian, the wood frog, have consistently shown reduced embryonic and larval tolerance to high-salinity roadside ponds, consistent with local maladaptation. We hypothesize that tradeoffs might mediate this maladaptive outcome, where embryonic and larval disadvantages are offset by advantages found at other life history stages. Here, we use data from an artificial fertilization experiment to investigate whether sperm performance and fertility differ between populations across a salinity pollution gradient. Specifically, we predict that roadside populations will harbor adaptive sperm motility variation that improves fertilization, potentially supporting a tradeoff between reproductive success and offspring performance. The results of this analysis underscore the nuanced impacts of environmental stressors on amphibian species, highlighting both maladaptive and adaptive responses across different life stages.

Primary Presenter: Sean Keane, Southern Connecticut State University (keanes2@southernct.edu)

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