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Mercury delays cerebellar development in a model songbird species, the zebra finch

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Abstract

Mercury exposure can disrupt development of the cerebellum, part of the brain essential for coordination of movement through a complex environment, including flight. In precocial birds, such as fowl, the cerebellum develops embryonically, and the chick is capable of leaving the nest within hours of hatching. However, most birds, including all songbirds, are altricial, and spend weeks in the nest between hatching and fledging. The objective of this study was to describe the normal development of the cerebellum in a model altricial songbird so as to determine the effect of exposure to mercury on cerebellar maturation. Adult zebra finch (Taeniopygia guttata) pairs were fed either a control diet, or a diet augmented with one of four treatment-levels of methylmercury (0.3–2.4 μg/g wet weight), and their offspring, the subjects of this study, were fed the same diet by parents. We documented, for the first time, the schedule of cerebellar development in an altricial bird, and compared stages of development among methylmercury-exposed groups. For all treatments of methylmercury, the age of completion of cellular migration was later than for control zebra finches, indicating a delay in cerebellar maturation. Displaced (heterotopic) Purkinje neurons, a pathology typical of methylmercury exposure in developing vertebrate brains, were more numerous in methylmercury-exposed birds, and persisted at least until the age of independence. Delays in maturation of the cerebellum could delay fledging in altricial bird species, with potential serious implications for the fitness of exposed individuals, as predation rates in the nest are often very high.

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Acknowledgements

All procedures with live vertebrate animals were approved by William & Mary’s Institutional Animal Care and Use Committee (2013-06-02-8721-dacris). Funding was provided by the Eastern Virginia Medical School/William & Mary Collaborative Grant program (to SAS and DAC), the National Science Foundation (IOS-1257590 to DAC, IOS-1257895 to MSS), National Institutes of Health (R15HD077624-01 to MSS), the Howard Hughes Medical Institute Undergraduate Science Education program grant to William & Mary, and E.I. DuPont de Nemours and Company (completed with oversight from the South River Science Team, which is a collaboration of state and federal agencies, academic institutions, and environmental interests). We are grateful to Margaret Whitney and Rachel Ellick for their skilled assistance on this study.

Funding

This study was funded by the Eastern Virginia Medical School/William & Mary Collaborative Grant program (to SAS and DAC), the National Science Foundation (IOS-1257590 to DAC, IOS-1257895 to MSS), National Institutes of Health (R15HD077624-01 to MSS), the Howard Hughes Medical Institute Undergraduate Science Education program grant to William & Mary, and E.I. DuPont de Nemours and Company (to DAC, completed with oversight from the South River Science Team, which is a collaboration of state and federal agencies, academic institutions, and environmental interests).

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Correspondence to Daniel A. Cristol.

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The authors declare that they have no conflicts of interest. Funders had no role in conceiving, analyzing or writing the study.

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All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. Procedures with live vertebrate animals were approved by William & Mary’s Institutional Animal Care and Use Committee (2013-06-02-8721-dacris).

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Scoville, S.A., Varian-Ramos, C.W., Adkins, G.A. et al. Mercury delays cerebellar development in a model songbird species, the zebra finch. Ecotoxicology 29, 1128–1137 (2020). https://doi.org/10.1007/s10646-020-02270-9

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  • DOI: https://doi.org/10.1007/s10646-020-02270-9

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