Data from: To breed or not to breed: endocrine response to mercury contamination by an Arctic seabird

Mercury, a ubiquitous toxic element, is known to alter expression of sex steroids and to impair reproduction across vertebrates but the mechanisms underlying these effects are not clearly identified. We examined whether contamination by mercury predicts the probability to skip reproduction in black-legged kittiwakes (Rissa tridactyla) from Svalbard. We also manipulated the endocrine system to investigate the mechanism underlying this relationship. During the pre-laying period, we injected exogenous GnRH (gonadotropin-releasing hormone) to test the ability of the pituitary to release luteinizing hormone (LH, a key hormone for the release of sex steroids and hence breeding) in relation to mercury burden. Birds that skipped reproduction had significantly higher mercury concentration in blood than breeders. Endocrine profiles of these birds also varied based on breeding status (breeders versus non-breeders), mercury contamination and sex. Specifically, in skippers (birds that did not breed), baseline LH decreased with increasing mercury concentration in males, whereas it increased in females. GnRH-induced LH levels increased with increasing mercury concentration in both sexes. These results suggest that mercury contamination may disrupt GnRH input to the pituitary. Thus, high mercury concentration could affect the ability of long-lived birds to modulate their reproductive effort (skipping or breeding) according to ongoing environmental changes in the Arctic, thereby impacting population dynamics.汞是一种无处不在的有毒元素，已知其可改变脊椎动物体内性类固醇的表达，并损害其繁殖能力，但此类效应背后的具体机制尚未明确。本研究旨在探究汞污染是否可预测斯瓦尔巴群岛黑脚三趾鸥（Rissa tridactyla）跳过繁殖的概率；同时通过操纵内分泌系统，对该关联背后的机制展开探究。在产卵前期，我们为受试鸥鸟注射外源性促性腺激素释放激素（gonadotropin-releasing hormone），以检测垂体释放黄体生成素（luteinizing hormone，LH）的能力与体内汞负荷的相关性——LH是介导性类固醇释放、进而调控繁殖过程的关键激素。结果显示，跳过繁殖的个体血液汞浓度显著高于繁殖个体；且此类个体的内分泌特征会因繁殖状态（繁殖者vs非繁殖者）、汞污染程度以及性别产生差异。具体而言，在未繁殖个体中，雄性的基础LH水平随血液汞浓度升高而降低，雌性则呈上升趋势；而在两性个体中，经GnRH诱导产生的LH水平均随汞浓度升高而升高。上述结果表明，汞污染可能会破坏GnRH对垂体的调控通路。因此，高浓度汞暴露或可影响长寿鸟类根据北极当前环境变化调节繁殖投入（选择跳过繁殖或开展繁殖）的能力，进而对种群动态产生影响。