Manganese Exacerbates Seasonal Health Declines in a Suicidally Breeding Mammal.

Reproductive costs must be balanced with survival to maximize lifetime reproductive rates; however, some organisms invest in a single, suicidal bout of breeding known as semelparity. The northern quoll (Dasyurus hallucatus) is an endangered marsupial in which males, but not females, are semelparous. Northern quolls living near mining sites on Groote Eylandt, Northern Territory, Australia, accumulate manganese (Mn) in their brains, testes, and hair, and elevated Mn impacts motor performance. Whether Mn is associated with other health declines is yet unknown. In the present study we show that male and female northern quolls with higher Mn accumulation had a 20% reduction in immune function and a trend toward reduced cortisol concentrations in hair. The telomere lengths of male quolls did not change pre- to postbreeding, but those with higher Mn levels had longer telomeres; in contrast, the telomeres of females shortened during the breeding season but recovered between the first year and second year of breeding. In addition, the telomeres of quolls that were recaptured declined at significantly higher rates in quolls with higher Mn between prebreeding, breeding, and/or postbreeding seasons. Future research should determine whether changes in cortisol, immune function, or telomere length affect reproductive output or survival-particularly for semelparous males. Environ Toxicol Chem 2024;43:74-86. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Exogenous iodide ameliorates perchlorate-induced thyroid phenotypes in threespine stickleback.

Perchlorate is a ubiquitous environmental contaminant that has widespread endocrine disrupting effects in vertebrates, including threespine stickleback (Gasterosteus aculeatus). The target of perchlorate is thyroid tissue where it induces changes in the organization, activation, and morphology of thyroid follicles and surrounding tissues. To test the hypothesis that some phenotypes of perchlorate toxicity are not mediated by thyroid hormone, we chronically exposed stickleback beginning at fertilization to perchlorate (10, 30, 100ppm) or control water with and without supplementation of either iodide or thyroxine (T4). Stickleback were sampled across a one-year timespan to identify potential differences in responses to treatment combinations before and after sexual maturation. We found that most thyroid histomorphological phenotypes induced by perchlorate (follicle proliferation, reduced follicle area (adults only), colloid depletion, thyrocyte hypertrophy (subadults only)) were significantly ameliorated by exogenous iodide supplementation. In contrast, treatment with exogenous T4 did not correct any of the thyroid-specific histopathologies induced by perchlorate. Whole-body thyroid hormone concentrations were not significantly affected by perchlorate exposure; however, supplementation with iodide and T4 significantly increased T4 concentrations. This study also revealed an increased erythrocyte area in the thyroid region of perchlorate-exposed adults, while lipid droplet number increased in perchlorate-exposed subadults. Increased erythrocyte area was ameliorated by both iodide and T4, while neither supplement was able to correct lipid droplet number. Our finding on lipid droplets indicates that exposure to perchlorate in early development may have obesogenic effects.

Perchlorate exposure does not modulate temporal variation of whole-body thyroid and androgen hormone content in threespine stickleback.

Previously we showed that exposure of threespine stickleback (Gasterosteus aculeatus) to the endocrine disruptor perchlorate results in pronounced structural changes in thyroid and gonad, while surprisingly, whole-body thyroid hormone concentrations remain unaffected. To test for hormone titer variations on a finer scale, we evaluated the interactive effects of time (diel and reproductive season) and perchlorate exposure on whole-body contents of triiodothyronine (T3), thyroxine (T4), and 11-ketotestosterone (11-KT) in captive stickleback. Adult stickleback were exposed to 100ppm perchlorate or control water and sampled at 4-h intervals across the 24-hday and at one time-point (1100h) weekly across the reproductive season (May-July). Neither whole-body T3 nor T4 concentration significantly differed across the day in control or perchlorate treated stickleback. Across the reproductive season, whole-body T3 concentration remained stable while T4 significantly increased. However, neither hormone concentration was significantly affected by perchlorate, verifying our previous studies. The concentration of whole-body 11-KT, a major fish androgen, displayed significant diel variation and also steadily declined across the reproductive season in untreated males; perchlorate exposure did not influence the concentration of 11-KT in either diel or reproductive season schedules. Diel and reproductive season variations in 11-KT content in male stickleback are likely related to reproductive physiology and behavior. The observed increase in T4 content across the reproductive season may be reflective of increased energy investment in reproduction near the end of the life cycle.