Abstract
The St. Lawrence River in Eastern Ontario, Canada, has been a designated an area of concern due to past industrial contamination of sediment in some areas and transport of mercury from tributaries. Previous research using bats as sentinel species identified elevated concentrations of total mercury (THg) in fur of local bats and species-specific variation between little brown bats (Myotis lucifugus) and big brown bats (Eptesicus fuscus). Here, we investigated the mercury exposure pathways for these two species by testing the hypothesis that diet variation, particularly the reliance on aquatic over terrestrial insects, is a determinant of local bat mercury concentrations. We analyzed THg concentration and stable isotope ratios of δ15N and δ13C in fur of little and big brown bats, and in aquatic and terrestrial insects. Big brown bats, especially males, accumulated significantly higher THg concentrations in their fur compared to little brown bats. However, this difference was not related to diet because big brown bats consumed terrestrial insects, which were lower in mercury than aquatic insects, the primary prey for little brown bats. We also evaluated whether fur THg concentrations translate into molecular changes in tissues linked to (methyl)mercury toxicity by quantifying tissue changes in global DNA methylation and mitochondrial DNA abundance. No significant changes in DNA molecular markers were observed in relation to fur THg concentration, suggesting mercury exposure to local bats did not impact molecular level changes at the DNA level. Higher mercury in bats was not associated with local aquatic contamination or genotoxicity in this study area.
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Acknowledgements
Funding in form of an NSERC-DG (JAM) and from the St. Lawrence River Institute (BCH) are gratefully acknowledged. The authors wish to thank Stephany Hildebrand, Lexy Harquail, Yanik Rozon, Emilie DeRouchie, and Harneet Cheema (St. Lawrence River Institute) for expert assistance with field work and the identification of insect samples. The authors also wish to acknowledge Emmanuel Yumvihoze and Paul Middlestead (University of Ottawa) for expert assistance in THg and stable isotope analyses, respectively.
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BB, BAH, JC and JAM conceived and planned the experiments. BB and BAH conducted field work and BAH provided access to the specimen bank. BB conducted analyses and generated data. BB, BAH, JC, JAM, analyzed the data and prepared the figures. All authors discussed the results, contributed to, reviewed and approved of the final manuscript.
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Bedard, B., Hickey, B., Chételat, J. et al. Variation in habitat use and its consequences for mercury exposure in two Eastern Ontario bat species, Myotis lucifugus and Eptesicus fuscus. Ecotoxicology 32, 845–857 (2023). https://doi.org/10.1007/s10646-023-02693-0
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DOI: https://doi.org/10.1007/s10646-023-02693-0