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

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 and 2019 varied from 1.2% to 16.7%, where temporal increases in abnormality rates were observed. We also performed a targeted, 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.