Short-term mercury exposure disrupts muscular and hepatic lipid metabolism in a migrant songbird

Abstract

Methylmercury (MeHg) is a global pollutant that can cause metabolic disruptions in animals and thereby potentially compromise the energetic capacity of birds for long-distance migration, but its effects on avian lipid metabolism pathways that support endurance flight and stopover refueling have never been studied. We tested the effects of short-term (14-d), environmentally relevant (0.5 ppm) dietary MeHg exposure on lipid metabolism markers in the pectoralis and livers of yellow-rumped warblers (Setophaga coronata) that were found in a previous study to have poorer flight endurance in a wind tunnel than untreated conspecifics. Compared to controls, MeHg-exposed birds displayed lower muscle aerobic and fatty acid oxidation capacity, but similar muscle glycolytic capacity, fatty acid transporter expression, and PPAR expression. Livers of exposed birds indicated elevated energy costs, lower fatty acid uptake capacity, and lower PPAR-γ expression. The lower muscle oxidative enzyme capacity of exposed birds likely contributed to their weaker endurance in the prior study, while the metabolic changes observed in the liver have potential to inhibit lipogenesis and stopover refueling. Our findings provide concerning evidence that fatty acid catabolism, synthesis, and storage pathways in birds can be dysregulated by only brief exposure to MeHg, with potentially significant consequences for migratory performance.

Light pollution enhances ground‐level exposure to airborne toxic chemicals for nocturnally migrating passerines

“…One of the best studied ATC examples for migrating passerine bird species are the effects of mercury (Hg) and methylmercury (MeHg) exposure, the latter being the most harmful and bioavailable form of Hg (Seewagen, 2020; Whitney & Cristol, 2017). Hg exposure adversely affects behaviors that require large amounts of energy (Whitney & Cristol, 2017), such as migratory flight (Gerson et al, 2019; Ma, Perez, et al, 2018; Seewagen et al, 2022), and birds that have been exposed to Hg on their breeding grounds are less likely to return the next breeding season (Ma, Branfireun, et al, 2018). Birds function as mid‐level consumers to apex predators and play an important role in the trophic transfer of Hg and other contaminants (Kuo et al, 2022).…”

Keystone seabird may face thermoregulatory challenges in a warming Arctic

“…Hg contamination may interfere with body temperature (T b ) regulation via endocrine disruption 25 , notably affecting production of thyroid hormones, which are central to thermoregulation 26 . In addition, Hg contamination could affect patterns of thermoregulation through effects on detoxification costs and resting metabolic rate 27 – 29 . Although few data specific to Hg are available, both hypo- and hyperthermic responses can occur in response to contamination 30 .…”

More than mortality: Consequences of human activity on migrating birds extend beyond direct mortality

“…Methylmercury exposure can impair birds' navigation and ability to fly (Ma et al 2018, Moye et al 2016). Additionally, exposure to lead and methylmercury can hinder migration by interfering with refueling and reducing flight endurance and performance through a variety of effects that include altered metabolism (Seewagen et al 2022), altered immune function (Lewis et al 2013, Vallverdú-Coll et al 2019), anorexia, lethargy, ataxia (Seewagen 2020, Pain et al 2019) diarrhea, convulsions, and paralysis (Pain et al 2019). Widespread environmental contaminants can thus negatively affect fitness by degrading the health, energetic condition, and orientation ability of migrating birds.…”