Complex Life Histories Alter Patterns of Mercury Exposure and Accumulation in a Pond-Breeding Amphibian

• Published in: Environmental science & technology Vol. 57; no. 10; pp. 4133 - 4142
• Main Authors: Rowland, Freya E., Muths, Erin, Eagles-Smith, Collin A., Stricker, Craig A., Kraus, Johanna M., Harrington, Rachel A., Walters, David M.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 14.03.2023
• Subjects: Amphibians; Amphibians - metabolism; Animals; Aquatic animals; Breeding; Catabolism; Contaminants; Contaminants in Aquatic and Terrestrial Environments; Decoupling; Diet; Dimethylmercury; Ecosystem; Environmental Monitoring; Fasting; Fishes - metabolism; Food Chain; Food chains; Food webs; Frogs; Hibernation; Larvae; Life cycles; Life history; Mercury; Mercury (metal); Mercury - analysis; Metamorphosis; Metapopulations; Methylmercury; Methylmercury Compounds - metabolism; Ontogeny; Ponds; Prey; Reptiles & amphibians; Water Pollutants, Chemical - analysis; methylmercury; stable isotopes; tadpole; metamorph; boreal chorus frog; contaminant; Anuran; bioaccumulation; biomagnification; Pseudacris maculata
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.2c04896

Quantifying how contaminants change across life cycles of species that undergo metamorphosis is critical to assessing organismal risk, particularly for consumers. Pond-breeding amphibians can dominate aquatic animal biomass as larvae and are terrestrial prey as juveniles and adults. Thus, amphibians can be vectors of mercury exposure in both aquatic and terrestrial food webs. However, it is still unclear how mercury concentrations are affected by exogenous (e.g., habitat or diet) vs endogenous factors (e.g., catabolism during hibernation) as amphibians undergo large diet shifts and periods of fasting during ontogeny. We measured total mercury (THg), methylmercury (MeHg), and isotopic compositions (δ 13C, δ15N) in boreal chorus frogs (Pseudacris maculata) across five life stages in two Colorado (USA) metapopulations. We found large differences in concentrations and percent MeHg (of THg) among life stages. Frog MeHg concentrations peaked during metamorphosis and hibernation coinciding with the most energetically demanding life cycle stages. Indeed, life history transitions involving periods of fasting coupled with high metabolic demands led to large increases in mercury concentrations. The endogenous processes of metamorphosis and hibernation resulted in MeHg bioamplification, thus decoupling it from the light isotopic proxies of diet and trophic position. These step changes are not often considered in conventional expectations of how MeHg concentrations within organisms are assessed.