Frequency of adult amphibian abnormalities and consequences for fitness-related traits in an uncontaminated environment

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Morphological abnormalities in amphibians are commonly associated with anthropogenic activity, although little baseline information on the prevalence of abnormalities in uncontaminated environments exist. Here, we leverage a 12-year study of spotted salamanders (Ambystoma maculatum Shaw, 1802) in an uncontaminated ecosystem in Algonquin Provincial Park, Canada, to estimate abnormality rates and explore how abnormalities affect fitness-related traits. Annual abnormality rates estimated from drift fence data, ranged from 4.3% to 5.8% of individuals sampled. Abnormality rates from aquatic trapping between 2008–2019 varied from 1.2% to 16.7%, where temporal increases in abnormality rate were observed. We also performed a targeted but systematic literature survey and found that Caudata exhibited a slightly higher abnormality prevalence than Anura, and that the baseline frequency of abnormalities described at our drift fence site is slightly lower than rates reported in the literature (8.1%, 95% CI, 4.76–13.3%). Salamanders with abnormalities exhibited a slightly, but not significantly, higher body condition and a significantly earlier arrival date at the breeding site, both of which are traits typically associated with high-fitness individuals. Our study suggests that abnormalities have detectable phenotypic consequences and underlines the need for temporal sampling efforts to provide ranges of baseline abnormality rates, rather than a point estimate.