Marasco, V. | Search bioRxiv

bioRxiv2026

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

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.

ecology↗

bioRxiv2023

Controlled expression of avian migratory fattening influences innate immune responses

While immunity is frequently suppressed when birds engage in strenuous migratory flights, whether and how immunity changes during the rapid accumulation of energy stores in preparation for migration remains largely unknown. Here, we induced pre-migratory fattening through controlled changes of daylight in common quails Coturnix coturnix and regularly assessed changes in a marker of constitutive innate immunity (Leukocyte Coping Capacity or LCC) and measures of body composition (lean and fat mass). LCC responses were highest in the mid-fattening phase and lowest when fattening was completed. At mid-fattening, we also found that the birds that kept a higher proportion of lean mass (i.e. accumulated less fat) had the highest LCC peaks. Our results indicate that migratory birds undergo rapid immunological changes as they accumulate energy stores for migration and propose that this could be due to competing or trade-off processes between metabolic remodelling and innate immune system function. Summary statementImmunity is vital when migrating to new environments. It is costly and competivite to other physiological processes. Here we bring new evidence on this process in migratory birds.

physiology↗