Mercury bioaccumulation varies across breeding-site height and life-history traits in Amazonian phytotelm-breeding frogs

Abstract

Mercury (Hg) concentrations in the environment have significantly increased in the Amazon. Despite the observed deleterious effects on freshwater wildlife, the impacts of Hg contamination in phytotelmata (i.e., waterbodies contained in plant structures) and the species therein remain undocumented. We investigated the effects of Hg contamination on a phytotelm-breeding frog community in an otherwise pristine rainforest in French Guiana. Total Hg concentrations were measured in 28 pools at different heights (i.e. ground to canopy), and in the bodies of 103 tadpoles from five species with contrasting life histories. Tadpoles from ground pools had higher Hg concentrations than those from arboreal pools, revealing a vertical gradient in Hg contamination; tadpoles from species with slow development and parental care (i.e., tadpole transport) exhibited higher Hg concentrations than those of species with fast development without parental care. Finally, although Hg burdens were not associated with oxidative DNA levels, individuals reaching metamorphosis exhibited lower DNA damage than early-stage tadpoles, possibly reflecting reduced oxidative damage resulting from cellular remodelling undergone during metamorphosis, or selective mortality processes. Our findings highlight the joint influence of habitat type and life-history traits on Hg accumulation and that, even in pristine forests, Hg exposure varies strongly across microhabitats and species.