Pesticide exposure and its interaction with other natural stressors can play a role in amphibian population declines because disruptions in stress hormone regulatory mechanisms may inhibit immune responses during metamorphosis. Here, we determined the interactive effects of predation risk and sublethal concentration of two pesticides on immunological and physiological responses in tadpoles of the tropical frog . Using mesocosms, we used chronic exposure to three levels of chlorothalonil and β-endosulfan in the presence or absence of Odonate larvae. Our results show that β-endosulfan in high concentrations reduced the weight of the tadpoles and increased the neutrophil count and corticosterone (CORT) levels. Larval development was accelerated by high concentrations of chlorothalonil. Also, this pesticide in low and high concentrations increases the absolute values of lymphocytes. Tadpoles exposed to chlorothalonil increased the numbers of monocytes (in low concentrations), and lymphocytes (in high and low concentrations). The interactions of the low concentrations of both pesticides with and without the predator's presence also increased the number of lymphocytes. A combination of pesticides increases the number of lymphocytes in the blood due to synergistic cytotoxicity. This study proves that β- endosulfan elevates circulating CORT and thus generates physiological stress in tadpoles. Given that both pesticides are widely used within the distribution of in Costa Rica, it is likely that tadpoles’ development and immune function are altered by pesticide use. In combination with stressors such as emerging diseases and altered precipitation regimes, widespread agrochemical uses likely caused this species enigmatic decline in recent decades.

中文翻译：

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Lithobates taylori（无尾蛇：蛙科）蝌蚪对捕食风险以及百菌清和β-硫丹亚致死浓度的免疫和生理反应


接触农药及其与其他自然应激源的相互作用可能会导致两栖动物种群数量下降，因为应激激素调节机制的破坏可能会抑制变态过程中的免疫反应。在这里，我们确定了两种农药的捕食风险和亚致死浓度对热带青蛙蝌蚪免疫和生理反应的相互作用影响。使用中生态系统，我们在存在或不存在Odonate幼虫的情况下长期暴露于三种水平的百菌清和β-硫丹。我们的结果表明，高浓度的β-硫丹减轻了蝌蚪的重量，并增加了中性粒细胞计数和皮质酮（CORT）水平。高浓度的百菌清加速了幼虫的发育。此外，这种农药在低浓度和高浓度下都会增加淋巴细胞的绝对值。接触百菌清的蝌蚪增加了单核细胞（低浓度）和淋巴细胞（高浓度和低浓度）的数量。两种低浓度杀虫剂在有或没有捕食者存在的情况下的相互作用也增加了淋巴细胞的数量。由于协同细胞毒性，多种杀虫剂的组合会增加血液中淋巴细胞的数量。这项研究证明，β-硫丹会升高循环 CORT，从而在蝌蚪中产生生理应激。鉴于这两种农药在哥斯达黎加分布范围内广泛使用，蝌蚪的发育和免疫功能可能会因农药的使用而改变。加上新出现的疾病和降水模式改变等压力因素，农用化学品的广泛使用可能导致该物种在近几十年来神秘地减少。