Department of Wildlife Ecology and Conservation, 110 Newins-Ziegler Hall, P.O. Box 110430, University of Florida, Gainesville, FL 32611, USA.
Aquat Toxicol. 2011 Oct;105(3-4):321-7. doi: 10.1016/j.aquatox.2011.07.003. Epub 2011 Jul 8.
Methylmercury is a globally distributed pollutant and upper trophic level aquatic fauna are at particularly high risk of exposure. Although methylmercury is known to have a number of neurological and developmental effects, relatively little is known about effects on endocrine disruption and reproduction in aquatic fauna, particularly in response to chronic exposure at low concentrations. We experimentally exposed captive white ibises for 3.5 years (2005-2008) to dietary methylmercury at three environmentally relevant concentrations (0.05, 0.1 and 0.3 ppm wet weight in diet). We measured fecal concentrations of estradiol and testosterone metabolites in two consecutive breeding seasons (2007 and 2008). When effects were controlled for stage of breeding, this resulted in altered estradiol and testosterone concentrations in adult breeders of both sexes. Changes in endocrine expression were not consistent over both years, and a clear dose-response relationship was not always present. Endocrine changes were, however, associated at all dose levels with changes in reproductive behavior, reduced reproductive success and altered mate choice in males. Male-male pairing and altered courtship behavior in males were related both to dose treatment and, in 2008, to a demasculinized pattern of endocrine expression. Changes in hormone concentrations of dosed homosexually paired males, when present, were in the same direction but at a higher magnitude than those in heterosexual dosed males. Dosed homosexual males showed decreased testosterone during nest-building and elevated testosterone during incubation when compared with their dosed heterosexual counterparts during the 2008 breeding season. In the same year, exposed males had elevated estradiol during courtship, but had decreased estradiol during other stages in comparison with controls. Dosed females generally showed decreased estradiol and testosterone concentrations compared to controls, albeit not with a clear dose-response effect. Our findings suggest that endocrine disruption due to chronic exposure to even low concentrations of dietary methylmercury may be a widespread mechanism by which reproduction is impaired in wild bird populations.
甲基汞是一种在全球范围内分布的污染物，处于较高营养级的水生动物特别容易受到暴露的影响。尽管已知甲基汞具有许多神经和发育方面的影响，但对于水生动物的内分泌干扰和生殖方面的影响相对较少，特别是在低浓度慢性暴露的情况下。我们在 2005 年至 2008 年期间，通过饮食将甲基汞以三种环境相关浓度（饮食中湿重的 0.05、0.1 和 0.3ppm）连续 3.5 年暴露于人工饲养的白鹮。我们在两个连续的繁殖季节（2007 年和 2008 年）测量了粪便中雌二醇和睾酮代谢物的浓度。当将繁殖阶段的影响控制起来时，这导致了两性成年繁殖者的雌二醇和睾酮浓度发生改变。内分泌表达的变化在两年中并不一致，也并不总是存在明确的剂量反应关系。然而，内分泌变化与所有剂量水平的雄性繁殖行为变化、繁殖成功率降低和伴侣选择改变有关。雄性之间的配对和雄性求偶行为的改变，与剂量处理有关，在 2008 年，与雄性去势内分泌表达模式有关。存在的情况下，接受同性配对的雄性的激素浓度变化方向与异性配对的雄性相同，但幅度更大。与异性配对的雄性相比，在 2008 年的繁殖季节中，接受同性配对的雄性在筑巢期间的睾酮水平降低，在孵化期间的睾酮水平升高。在同一年，与对照组相比，暴露的雄性在求偶期间的雌二醇水平升高，但在其他阶段的雌二醇水平降低。与对照组相比，受影响的雌性一般表现出雌二醇和睾酮浓度降低，尽管没有明确的剂量反应效应。我们的研究结果表明，由于慢性暴露于饮食中的低浓度甲基汞而导致的内分泌干扰，可能是野生鸟类种群繁殖受损的一种普遍机制。
