[MARMAM] New publication: Mercury and cortisol interact to influence endocrine and immune biomarkers in elephant seals

Rachel Holser rholser at ucsc.edu
Mon Jun 12 07:19:28 PDT 2023

Dear All,

On behalf of my co-authors, I'm happy to share our new publication entitled
"Mercury bioaccumulation and cortisol interact to influence endocrine and
immune biomarkers in a free-ranging marine mammal".  The abstract and link
to the article are below, and anyone interested is welcome to request a PDF
via email or ResearchGate.

Mercury bioaccumulation from deep-ocean prey and the extreme life history
strategies of adult female northern elephant seals (*Mirounga
angustirostris*) provide a unique system to assess the interactive effects
of mercury and stress on animal health by quantifying blood biomarkers in
relation to mercury (skeletal muscle and blood mercury) and cortisol
concentrations. The thyroid hormone thyroxine (tT4) and the antibody
immunoglobulin E (IgE) were associated with mercury and cortisol
concentrations interactively, where the magnitude and direction of the
association of each biomarker with mercury or cortisol changed depending on
the concentration of the other factor. For example, when cortisol
concentrations were lowest, tT4 was positively related to muscle mercury,
whereas tT4 had a negative relationship with muscle mercury in seals that
had the highest cortisol concentrations. Additionally, we observed that two
thyroid hormones, triiodothyronine (tT3) and reverse triiodothyronine
(rT3), were negatively (tT3) and positively (rT3) associated with mercury
concentrations and cortisol in an additive manner. As an example, tT3
concentrations in late breeding seals at the median cortisol concentration
decreased by 14% across the range of observed muscle mercury
concentrations. We also observed that immunoglobulin M (IgM), the
pro-inflammatory cytokine IL-6 (IL-6), and a reproductive hormone,
estradiol, were negatively related to muscle mercury concentrations but
were not related to cortisol. Specifically, estradiol concentrations in
late molting seals decreased by 50% across the range of muscle mercury
concentrations. These results indicate important physiological effects of
mercury on free-ranging apex marine predators and interactions between
mercury bioaccumulation and extrinsic stressors. Deleterious effects on
animals’ abilities to maintain homeostasis (thyroid hormones), fight off
pathogens and disease (innate and adaptive immune system), and successfully
reproduce (endocrine system) can have significant individual- and
population-level consequences.



Rachel Holser, Ph.D.
Assistant Research Biologist
Institute of Marine Sciences
University of California, Santa Cruz
115 McAllister Way
Santa Cruz, CA 95060
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