SGER: Characterization of Hermaphroditism in Rana Pipiens

先前的实验室研究表明，除草剂阿特拉津（atrazine）会导致非洲爪蛙（Xenopus laevis）和美洲豹蛙（Rana pipiens）的性异常。雌雄同体（动物有两个睾丸和卵巢或睾丸有发育中的卵子）是观察到的最严重的异常。后来的研究表明，在野外通过农业径流暴露于阿特拉津的人群中也发现了类似的异常情况。虽然实验室数据支持因果关系假说，但雌雄同体可能是自然发生的，与野生环境中阿特拉津污染的相关性可能是巧合。目前的研究将从两个方面解决这种可能性：1)将在实验室中饲养野生种群中表现出雌雄同体的动物，以确定在没有接触阿特拉津污染的水的情况下是否会出现雌雄同体。来自这些种群的动物的发育将与来自在野外没有雌雄同体现象的种群的动物进行比较。2)在野生环境中没有雌雄同体现象的动物将被饲养在被阿特拉津污染的水中，这些水是从在野生环境中观察到雌雄同体现象的地区收集的，以确定它是否会导致通常不表现出这种发育模式的动物出现雌雄同体现象。上述两个目标将决定雌雄同体是自然发生，还是污染暴露的结果。这些研究之所以重要，有几个原因：1)阿特拉津是地表水和饮用水中最常见的污染物；2)实验室研究表明，阿特拉津的活性水平低至十亿分之0.1，即使在雨水中也可能超过这一水平；3)阿特拉津等农药可能与两栖动物数量下降有关；4)阿特拉津影响两栖动物的内分泌机制已在鱼类、爬行动物和哺乳动物中得到证实；5)同样的机制可能导致由阿特拉津在大鼠中产生的癌症，以及在职业接触阿特拉津的人类中观察到的癌症（乳腺癌和前列腺癌）。

Previous laboratory studies showed that the herbicide, atrazine, induced sexual abnormalities in both African clawed frogs (Xenopus laevis) and American leopard frogs (Rana pipiens). Hermaphroditism (animals with both testes and ovaries or testes with developing eggs) was the most severe abnormality observed. Later studies showed that similar abnormalities were found in the wild in populations exposed to atrazine via agricultural runoff. Although the cause-effect hypothesis is supported by laboratory data, it is possible that hermaphroditism occurs naturally and that the correlation with atrazine contamination in the wild may be coincidental. The current study will address the possibility in two ways: 1) Animals from populations in the wild that show hermaphroditism will be reared in the laboratory to determine if hermaphroditism occurs in the absence of exposure to atrazine-contaminated water. Development of animals from these populations will be compared with animals from populations that do not show hermaphroditism in the wild. 2) Animals from populations that do not show hermaphroditism in the wild will be reared in atrazine-contaminated water collected from areas where hermaphroditism was observed in the wild to determine if it will induce hermaphroditism in animals that do not normally show this developmental pattern.The two aims outlined above will determine if hermaphroditism occurs naturally, or is the result of contaminant exposure. These studies are important for several reasons: 1) atrazine is the most common contaminant in ground and drinking water; 2) laboratory studies showed that atrazine is active at levels as low as 0.1 parts per billion, a level that can be exceeded even in rain water; 3) atrazine and other pesticides may be involved in amphibian declines; 4) the proposed endocrine mechanisms by which atrazine affects amphibians have been documented in fish, reptiles, and mammals; 5) the same mechanisms may be responsible for cancers produced in rats by atrazine and observed in humans occupationally exposed to atrazine (breast and prostate cancer).