Freeman Jennifer L, Beccue Nathan, Rayburn A Lane
University of Illinois, Department of Crop Sciences, 1201 W. Gregory Drive, 320 ERML, Urbana, IL 61801, USA.
Aquat Toxicol. 2005 Nov 10;75(3):263-76. doi: 10.1016/j.aquatox.2005.08.012. Epub 2005 Oct 6.
Pesticide chemical contamination is one of the suspected contributors of the amphibian population decline. The herbicide atrazine is one of the major surface water contaminants in the U.S. A previous study has shown that atrazine at concentrations as low as 100 parts per billion (ppb) increased the time to metamorphosis in Xenopus laevis tadpoles. However, questions remain as to the applicability of a study of a non-native species to a native organism. The possible effects of atrazine on developing Bufo americanus were explored. Atrazine at potentially (albeit high) environmental concentrations was found not to delay the metamorphosis of developing B. americanus tadpoles as observed in X. laevis. Several studies have indicated that atrazine affects thyroid hormones. Since thyroid hormones are critical in amphibian metamorphosis, B. americanus and X. laevis tadpoles were exposed to exogenous 3,5,3'-triiodothyronine (T3). X. laevis were found to be more responsive to the effects of exogenous T3 compared to B. americanus, indicating that X. laevis may be more sensitive to endocrine active chemicals than B. americanus. In X. laevis, nuclear heterogeneity has been associated with metamorphosis. Flow cytometric analysis of the nuclei of normal metamorphing B. americanus indicates a decrease in the amount of thyroid mediated chromatin alterations relative to the nuclei of metamorphing X. laevis. Indications are that the differential response to endocrine disruption is due to the differential role of chromatin associated gene expression during metamorphosis of B. americanus versus X. laevis. A second native species, Hyla versicolor, was observed to have the X. laevis nuclear pattern with respect to metamorphosis. As such, sensitivity to endocrine disruption is hypothesized not to be limited to laboratory non-native species.
农药化学污染是两栖动物数量减少的疑似原因之一。除草剂阿特拉津是美国地表水中的主要污染物之一。此前的一项研究表明，浓度低至十亿分之一百（ppb）的阿特拉津会延长非洲爪蟾蝌蚪的变态时间。然而，关于非本地物种的研究对本地生物的适用性仍存在疑问。本研究探讨了阿特拉津对美国蟾蜍发育的可能影响。研究发现，在潜在的（尽管很高）环境浓度下，阿特拉津并不会像在非洲爪蟾中观察到的那样延迟美国蟾蜍蝌蚪的变态。多项研究表明，阿特拉津会影响甲状腺激素。由于甲状腺激素在两栖动物变态过程中至关重要，因此将美国蟾蜍和非洲爪蟾蝌蚪暴露于外源性3,5,3'-三碘甲状腺原氨酸（T3）中。结果发现，与美国蟾蜍相比，非洲爪蟾对外源性T3的影响更敏感，这表明非洲爪蟾可能比美国蟾蜍对内分泌活性化学物质更敏感。在非洲爪蟾中，核异质性与变态有关。对正常变态的美国蟾蜍细胞核进行流式细胞术分析表明，相对于变态的非洲爪蟾细胞核，甲状腺介导的染色质改变量有所减少。这表明对内分泌干扰的差异反应是由于美国蟾蜍与非洲爪蟾变态过程中染色质相关基因表达的不同作用所致。观察到另一种本地物种变色树蛙在变态方面具有非洲爪蟾的核模式。因此，推测对内分泌干扰的敏感性不仅限于实验室中的非本地物种。
