Blood Mercury Levels of Zebra Finches Are Heritable: Implications for the Evolution of Mercury Resistance

Abstract

Mercury is a ubiquitous metal contaminant that negatively impacts reproduction of wildlife and has many other sub-lethal effects. Songbirds are sensitive bioindicators of mercury toxicity and may suffer population declines as a result of mercury pollution. Current predictions of mercury accumulation and biomagnification often overlook possible genetic variation in mercury uptake and elimination within species and the potential for evolution in affected populations. We conducted a study of dietary mercury exposure in a model songbird species, maintaining a breeding population of zebra finches (Taeniopygia guttata) on standardized diets ranging from 0.0–2.4 μg/g methylmercury. We applied a quantitative genetics approach to examine patterns of variation and heritability of mercury accumulation within dietary treatments using a method of mixed effects modeling known as the 'animal model'. Significant variation in blood mercury accumulation existed within each treatment for birds exposed at the same dietary level; moreover, this variation was highly repeatable for individuals. We observed substantial genetic variation in blood mercury accumulation for birds exposed at intermediate dietary concentrations. Taken together, this is evidence that genetic variation for factors affecting blood mercury accumulation could be acted on by selection. If similar heritability for mercury accumulation exists in wild populations, selection could result in genetic differentiation for populations in contaminated locations, with possible consequences for mercury biomagnification in food webs.

Association between Chromosome 4 and mercury accumulation in muscle of the three‐spined stickleback (Gasterosteus aculeatus)

“…Thus, there is empirical evidence that pollutants may act as one of the selective forces in the environment and that genetic adaptation to pollutants is both possible and can occur naturally. Empirical results from family based experiments also show that accumulation of mercury in the body is highly heritable in steelheads (Blanc et al, 2003 ) and zebra finches (Buck et al, 2016 ). The fact that a strong genetic component is observed in such disparate taxa strengthens the assumption that genetic differences generally affect mercury accumulations in vertebrates.…”

Integrative behavioral ecotoxicology: bringing together fields to establish new insight to behavioral ecology, toxicology, and conservation

“…Since behavior is linked to fitness, either through behavioral or other physiological mechanisms, there is likely strong selection occurring at contaminated sites for resistant genotypes. If genetic variation exists for sensitivity to contaminants ( Buck et al 2016 ), then populations with long-term exposure might have evolved adaptations to these contaminants. Such variation has been demonstrated in some cases ( Pease et al 2010 ; Varian-Ramos et al 2013 ) and there are examples of pollutant resistant populations ( Brown et al 2016 ; Tüzün et al 2015 ).…”

“…If behavioral adaptations exist within contaminated populations, it may result in an underestimate of the risks posed by contaminants when behaviors in exposed populations are compared with populations from uncontaminated areas ( Morgan et al 2007 ). To avoid this, common garden experiments could be performed to detect any adaptations to contamination that may have evolved, and/or researchers could assess the heritability of traits associated with contaminant load and contaminant resistance ( Buck et al 2016 ).…”

Electrochemical Biosensor Using DNA Embedded Phosphorothioate Modified RNA for Mercury Ion Determination

“…If the level of mercury in organs exceeds the normal limit, its toxicity will cause long-term adverse effects on biological systems such as nervous, renal, motor, immune, and reproductive. The symptoms of health problems include memory deficit, increased fatigue, decreased muscular strength, plasma creatinine level brain damage, kidney failure, and various motion disorders. , To ensure environmental and food safety, the US Environmental Protection Agency (EPA) sets the maximum allowable mercury level in drinking water at 10 nM, and the China Food and Drug Administration requires the total mercury level in grain and vegetables to be below 0.02 mg/kg and 0.01 mg/kg, respectively.…”

“…The symptoms of health problems include memory deficit, increased fatigue, decreased muscular strength, plasma creatinine level brain damage, kidney failure, and various motion disorders. 11,12 To ensure environmental and food safety, the US Environmental Protection Agency (EPA) sets the maximum allowable mercury level in drinking water at 10 nM, and the China Food and Drug Administration requires the total mercury level in grain and vegetables to be below 0.02 mg/kg and 0.01 mg/kg, respectively. Rapid and accurate determination of the concentration of mercury is in increasing demand to evaluate environmental and food safety.…”